JP2004349817A - Parametric speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parametric speaker capable of varying a distance between an electroacoustic transducer and a position where an audible sound is generated with a simple structure. <P>SOLUTION: The parametric speaker 1 is provided with: an oscillator 11 for generating a voltage vibrating signal with a frequency of an ultrasonic band; an amplitude modulator 12 for applying amplitude modulation to the signal generated by the oscillator 11 on the basis of a sound signal; and an electroacoustic transducer 2 converting a modulated signal modulated by the amplitude modulator 12 into an ultrasonic wave and emitting the wave in air. The oscillation means 11 comprises a voltage-controlled oscillator 111 and a carrier generating section 112, and the oscillated frequency of which is variable. The parametric speaker 1 can vary the distance between the electroacoustic transducer 2 and the position at which the audible sound is generated resulting from an ultrasonic wave emitted from the electroacoustic transducer 2 subjected to self-demodulation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ただし、上記式において、ｃは音速、Ｓはポート部（放音孔）の開口面積、Ｖは共鳴室の容積、Ｌはポート部の長さ（図２中のＬで示す長さ）である。
【００４０】
以下、上記式に基づいて、例えばある実施例における共鳴周波数νを計算する。Ｓ＝５０μｍ×５０μｍ、Ｌ＝５０μｍ、Ｖ＝１００μｍ×１００μｍ×１．５ｍｍの共鳴器を考えると、共鳴周波数νは約９９ｋＨｚである。この場合、後述するパラメトリックスピーカ１において、この共鳴周波数νの近傍の発振周波数ν_２を使うことにより、さらに高い効率で空気にエネルギーを伝達させることができる。ただし、実際の共鳴器６は複雑な幾何学的構造を持つため、上記のような計算値は目安に留め、実物での合わせこみが望ましい。こうすれば、より低パワー（低消費電力）で高効率なパラメトリックスピーカ１が得られる。
【００４１】
また、電気音響変換器２は、クーロン力（静電気力）によって振動板２２１を振動（変位）させるので、低電圧での駆動でも変位量が大きく、また、高い制御性が得られる。よって、電気音響変換器２を用いたパラメトリックスピーカ１では、電力消費量の低減を図りつつ、高い音質が得られる。さらに、耐久性、加工性に優れ、量産にも適する。
【００４２】
以下、上述したような電気音響変換器アレイ１０を備えるパラメトリックスピーカ１の全体構成について説明する。
図３に示すように、パラメトリックスピーカ１は、電気音響変換器アレイ１０と、発振手段（搬送波発生手段）１１と、振幅変調器（振幅変調手段）１２と、各電気音響変換器２に対してそれぞれ設けられた増幅器（増幅手段）１３と、音声入力インターフェース１４と、位相制御手段１５と、位相制御インターフェース１７と、搬送波制御インターフェース１９とを備えている。なお、図３中では、図面の都合上、電気音響変換器２の数を１１個としているが、実際には電気音響変換器アレイ１０の各電気音響変換器２にそれぞれ被変調信号が入力される。
【００４３】
発振手段１１は、超音波帯域の周波数（約２０ｋＨｚ以上）で電圧が振動する信号（搬送波）を生成（発生）する。発振手段１１の発振周波数（搬送波の周波数）ν_２は、超音波帯域であれば特に限定されないが、２０ｋＨｚ〜４００ｋＨｚ程度であるのが好ましく、４０ｋＨｚ〜１００ｋＨｚ程度であるのがより好ましい。
【００４４】
この発振手段１１は、電圧制御発振器（Ｖｏｌｔａｇｅ Ｃｏｎｔｒｏｌｌｅｄ Ｏｓｃｉｌｌａｔｏｒ）１１１と、搬送波発生回路１１２とで構成されている。電圧制御発振器１１１は、その発振周波数が印加電圧の変化に伴って変化する発振器である。電圧制御発振器１１１への印加電圧を変えることにより、発振手段１１の発振周波数（すなわち、パラメトリックスピーカ１における搬送波の周波数）ν_２を変えることができる。
【００４５】
電圧制御発振器１１１には、搬送波制御インターフェース１９を介して、搬送波制御信号が入力される。搬送波制御信号は、パラメトリックスピーカ１が備える図示しない制御手段により生成される。この搬送波制御信号は、電圧制御発振器１１１に対する印加電圧を制御することにより、発振手段１１の発振周波数ν_２を制御する。なお、本発明では、このような構成と異なり、発振手段１１の発振周波数ν_２を手動で調整可能なものであってもよい。
【００４６】
電圧制御発振器１１１は、前記搬送波制御信号による制御に基づき、発振する。電圧制御発振器１１１が発振した信号は、搬送波発生回路１１２を介して振幅変調器１２に入力される。
搬送波発生回路１１２は、電圧制御発振器１１１が発振した信号に対し、例えば分周、波形整形等の処理を行うものである。
【００４７】
図示しない音声信号生成器で生成された音声信号は、音声入力インターフェース１４を介して振幅変調器１２に入力される。振幅変調器１２は、この音声信号に基づいて、発振手段１１から発振された信号、すなわち搬送波を振幅変調する。振幅変調器１２における振幅変調方式は、特に限定されず、通常の振幅変調方式のものでもよく、また、信号の包絡をもって振幅変調する包絡変調方式でもよい。
【００４８】
位相制御手段１５は、各電気音響変換器２に対してそれぞれ設けられた移相器（移相手段）１６を有している。この位相制御手段１５は、位相制御インターフェース１７を介して入力された位相制御信号に基づき、各移相器１６によって各電気音響変換器２に入力される被変調信号の位相を変化させることができる。移相器１６の種類は、特に限定されず、電気的なものでも、機械的なものでもよい。また、移相器１６は、位相を連続的に変化させ得るものでも、段階的に変化させるものでもよい。
前記位相制御信号は、パラメトリックスピーカ１が備える図示しない制御手段により、生成される。
【００４９】
振幅変調器１２によって変調された被変調信号は、位相制御手段１５の複数の移相器１６にそれぞれ入力される。各移相器１６を通った被変調信号は、各増幅器１３に入力され、電気音響変換器２を駆動可能なレベルに増幅される。各増幅器１３で増幅された被変調信号は、電気音響変換器アレイ１０の各電気音響変換器２に入力される。各電気音響変換器２は、この入力された信号を超音波に変換し、空中に、指向性を持って放射する。なお、移相器１６は、図示と異なり、電気音響変換器２と増幅器１３との間に設けられていてもよい。
【００５０】
電気音響変換器アレイ１０から空中に放射された超音波（被変調波）は、空気の非線形特性によって歪み波となり、空気中を伝播中に元の音声信号の可聴音に復調される。この復調された可聴音は、元の超音波の超指向特性を持っているため、パラメトリックスピーカ１は、所望の特定空間（特定方向）に対してのみ音響放射を行うことができる。
【００５１】
上記のようなパラメトリックスピーカ１の原理について、図４に基づいてさらに説明する。図４（ａ）は、伝送波、すなわち音声信号生成器から出力された音声信号の波形である。図４（ｂ）は、発振手段１１で生成された信号（搬送波）の波形である。この搬送波を伝送波にのせることによって、伝送波は、図４（ｃ）のような被変調波（被変調信号）に変換される。この被変調波を空中に放射すると、空気の非線形特性により空気が順方向に震動するときには早く進み、空気が逆方向に進むときには遅く進むことから、音波は、図４（ｄ）のように歪んでゆき、元の可聴音が復調されていく（図４（ｅ））。この復調された可聴音は、元の超音波と同様の指向性を持っている。
【００５２】
本発明のパラメトリックスピーカ１では、前述したように発振手段１１の発振周波数ν_２が可変であり、この発振周波数ν_２を変えることにより、各電気音響変換器２（電気音響変換器アレイ１０）から放射された超音波が自己復調して可聴音が発生（再生）する位置（以下、「可聴音発生位置」という）までの距離を変えることができる。
なお、電気音響変換器２から放射された超音波は、徐々に減衰・自己復調して可聴音に変わるので、可聴音発生位置は必ずしも厳密に定められるものではないが、本明細書でいう可聴音発生位置とは、人の耳に実質的に聞こえる程度の可聴音が発生する概略の位置を言うものとする。
【００５３】
本発明のパラメトリックスピーカ１において、電気音響変換器２から可聴音発生位置までの距離を変えることができるのは、次のような理由によるものである。
本発明者の知見によれば、パラメトリックスピーカ１では、各電気音響変換器２から放射される超音波は、伝播する間に、その波長λが短いほど早く減衰・自己復調し、波長λが長いほど減衰・自己復調するのが遅い。当該超音波の周波数は、発振手段１１の発振周波数ν_２と同じであるので、波長λは、空中での音速をｃとすると、λ＝ｃ／ν_２で与えられる。よって、パラメトリックスピーカ１では、発振周波数ν_２を高くするほど、超音波の波長λが短くなって各電気音響変換器２（電気音響変換器アレイ１０）から可聴音発生位置までの距離を近くすることができ、逆に、発振周波数ν_２を低くするほど、超音波の波長λが長くなって各電気音響変換器２（電気音響変換器アレイ１０）から可聴音が発生する位置までの距離を遠くすることができる。
【００５４】
例えば、図５の（１）に示すように、発振周波数ν_２が比較的低いｆ_１（例えば４０ｋＨｚ程度）である場合には、電気音響変換器アレイ１０から可聴音発生位置までの距離Ｄ_１は、比較的長い。この場合、聴取者は、電気音響変換器アレイ１０から距離Ｄ_１以上離れたところにいる場合に音を聞くことができる。
これに対し、図５の（２）に示すように、発振周波数ν_２が比較的高いｆ_２（例えば１００ｋＨｚ程度）である場合には、電気音響変換器アレイ１０から可聴音発生位置までの距離Ｄ_２は、比較的短い（Ｄ_２＜Ｄ_１）。この場合、聴取者は、電気音響変換器アレイ１０から距離Ｄ_２以上離れたところにいる場合に音を聞くことができる。
【００５５】
本発明のパラメトリックスピーカ１では、上記のようにして、電気音響変換器アレイから可聴音発生位置までの距離を変えることができるが、これにより、次のような利点がある。
第１の利点として、電気音響変換器アレイ１０と聴取者との距離に応じて可聴音発生位置を調整することにより、聴取者への音声の伝達効率を向上することができる。すなわち、聴取者になるべく近い位置で自己復調がなされるように可聴音発生位置を調整することにより、発生した可聴音が聴取者に届くまでの間に減衰するのを防止して、聴取者に効率良く音声を伝達することができる。
第２の利点として、電気音響変換器アレイ１０と聴取者との距離に応じて可聴音発生位置を調整することにより、聴取者の身体に超音波による悪影響を及ぼすのを防止することができる。
【００５６】
一方、従来のパラメトリックスピーカのように、可聴音発生位置の調整ができない場合には、例えば次のような不都合がある。
まず、図５の（１）に示す状態に可聴音発生位置が固定されているパラメトリックスピーカでは、電気音響変換器アレイ１０からの距離がＤ_１よりも近い距離（例えばＤ_２の距離）に聴取者がいる場合には、聴取者に音が聞こえないという不都合がある。また、この場合には、超音波が減衰しないままに聴取者に浴びせられ、聴取者が直接に超音波にさらされることとなるので、聴取者の身体に悪影響を及ぼすおそれもある。
【００５７】
次に、図５の（２）に示す状態に可聴音発生位置が固定されているパラメトリックスピーカでは、聴取者が電気音響変換器アレイ１０からＤ_１の距離にいる場合、距離Ｄ_２の位置で発生した可聴音が聴取者に届くまでの間に減衰して小さくなってしまい、聞こえが悪くなってしまうという不都合がある。
このように、可聴音発生位置の調整ができない場合には、電気音響変換器アレイ１０と聴取者との距離が変わると不都合が生じてしまい、当該距離の変化に対応することができない。
【００５８】
これに対し、本発明では、図５に示すように、聴取者が電気音響変換器アレイ１０からＤ_１の距離にいる場合と、Ｄ_２の距離にいる場合とで、発振周波数ν_２をｆ_１とｆ_２とに切り替えることにより、いずれの場合であっても上記のような不都合を生じることなく聴取者に音声を良好に伝達することができる。すなわち、本発明のパラメトリックスピーカ１では、電気音響変換器アレイ１０と聴取者との距離の変化に応じて可聴音発生位置を調整することにより、聴取者に対する音声の伝達を常に良好に行うことができる。
【００５９】
なお、図５に示す例では、可聴音発生位置の調整を２段階で行っているが、これは一例であり、本発明では、可聴音発生位置の調整を３段階以上の多段階で行うものでもよく、また、可聴音発生位置の調整を連続的に（無段階に）行うことができるように構成されていてもよい。さらに、可聴音発生位置の調整は、聴取者との距離を検知するセンサーを設けるなどして自動的に制御してもよく、あるいは手動で調整するようにしてもよい。
【００６０】
また、本実施形態のパラメトリックスピーカ１は、位相制御手段１５によって各電気音響変換器２に入力される被変調信号の位相を変化させることにより、発生する音の指向方向や、発生する音の指向性の度合いを変える（変更する）ことができるものである。
まず、位相制御手段１５が各電気音響変換器２に入力される被変調信号の位相を変化させない状態（各電気音響変換器２間に位相差を生じさせない状態）について説明する。以下、この状態を基準状態という。
【００６１】
基準状態では、電気音響変換器アレイ１０から放射される超音波は、電気音響変換器２の配列面１０１の法線方向に進むので、電気音響変換器アレイ１０が発生する音の指向方向は、配列面１０１の法線方向と同じ方向になる。
なお、上記配列面１０１とは、電気音響変換器アレイ１０において電気音響変換器２が並ぶ面（面方向）のことを言う。
また、基準状態では、電気音響変換器アレイ１０から放射される超音波は、図７中の点線で示すように、その放射角度（広がり角度）がゼロに近く、電気音響変換器アレイ１０から離れても外側に広がっていかない。よって、基準状態では、発生する音の指向性の度合いが強い。
【００６２】
次に、上述のような基準状態に対し、音の指向方向を配列面１０１の法線方向に対し角度θだけ傾斜した方向にする場合について、図６に基づき説明する。この場合には、位相制御手段１５は、各電気音響変換器２に入力される被変調信号の位相が電気音響変換器アレイ１０の一端側（図６中での左側）から他端側（図６中での右側）に向かって順次遅れる状態となるように制御する。
【００６３】
具体的には、位相制御手段１５は、電気音響変換器２の配列ピッチをｄ、電気音響変換器アレイ１０が放射する超音波の波長をλとしたとき、各電気音響変換器２に入力される被変調信号の位相が、図６中の左側から右側に向かって、（ｄ・ｓｉｎθ／λ）×３６０°ずつ遅れるような状態とする。
また、位相制御手段１５は、図６の紙面に垂直な方向に並ぶ各列の電気音響変換器２については、入力される被変調信号の位相が列ごとに互いに同じになるように制御する。
【００６４】
このような状態とすることにより、各電気音響変換器２から放射される超音波の波面２００は、図６に示すような位置関係のときに同位相になるので、これらの波面２００が重なり合い、配列面１０１に対し角度θだけ傾斜した波面３００が発生する。電気音響変換器アレイ１０が放射する超音波は、波面３００に垂直な方向に進むので、この状態では、音の指向方向は、図６中の大きい矢印で示すように、配列面１０１の法線方向に対し角度θだけ傾斜した方向となる。
【００６５】
言うまでもなく、被変調信号の位相を順次遅らせる方向を上記と逆にすれば、音の指向方向の傾斜方向を図６と逆にすることができる。
また、被変調信号の位相を順次遅らせる方向を上記と垂直な方向にすれば、音の指向方向の傾斜方向を図６の場合と垂直な方向することができる。すなわち、パラメトリックスピーカ１では、音の指向方向を、図１中の縦方向にも横方向にも傾斜させることができる。さらに、この縦方向の傾斜と横方向の傾斜とを組み合わせることにより、音の指向方向を図１中の斜めの方向に傾斜させることもできる。
【００６６】
このようにして、本実施形態のパラメトリックスピーカ１では、電気音響変換器アレイ１０の姿勢を変えることなく、音の指向方向をあらゆる方向に変えることができる。よって、人がいる方向に追従して音を向けるような使い方をする場合であっても、電気音響変換器アレイ１０の姿勢を変える機構を設ける必要がないので、構造の簡素化が図れる。
【００６７】
次に、前記基準状態に対し、音の放射角度（広がり角度）を大きくし、音の指向性の度合いが比較的弱い状態にする場合について図７に基づき説明する。
なお、ここでは、図７に示すように、音の放射角度（広がり角度）を図７中の左・右それぞれ２５°ずつとする場合を例に説明し、また、空中での音速ｃを３５０ｍ／ｓ、放射される超音波の周波数を５０ｋＨｚ、波長λを７ｍｍ、電気音響変換器２の配列ピッチｄを３．５ｍｍとするが、これらの各条件がこれに限定されないことは言うまでもない。
【００６８】
図７に示す場合、位相制御手段１５は、各電気音響変換器２に入力される被変調信号の位相が電気音響変換器アレイ１０の中央部から端に向かって順次遅れ、かつ、隣接する電気音響変換器２間での位相差が電気音響変換器アレイ１０の中央部から端に向かって順次増大する状態となるように制御する。
具体的には、図７に示す状態では、位相制御手段１５は、各電気音響変換器２に入力される被変調信号の位相が中央部に位置する電気音響変換器２に対して下記表１中の最右列に示す位相遅れを持つように制御する。なお、以下の説明では、図７中に示される１１個の電気音響変換器２を区別するために、便宜上、同図中の左側から右側に向かって順に０番〜１０番の番号を付ける。下記表１中の「番号」とは、この番号のことである。
【００６９】
【表１】

【００７０】
各電気音響変換器２に入力される被変調信号の位相を表１に示すように制御することにより、図７中の５番（中央）の電気音響変換器２からの超音波の放射方向は、配列面１０１の法線方向になり、他の各電気音響変換器２から放射方向は、この５番から両側に向かって順次、５°、１０°、１５°、２０°、２５°の傾斜角度を配列面１０１の法線方向に対して持つようになる。
【００７１】
なお、各電気音響変換器２について、表１の最右列に示す位相遅れは、次のようにして算出することができる。まず、各電気音響変換器２について、（ｄ・ｓｉｎθ／λ）×３６０°で得られる隣接する電気音響変換器２との位相差を計算し、これを５番の電気音響変換器２から両側に向かって累積することにより、表１の最右列に示す位相遅れが得られる（表１参照）。
このようにして、パラメトリックスピーカ１では、音の指向性の度合い（強弱）を変化させることができるので、音を向ける範囲の広狭を容易に調整することができる。また、位相制御手段１５による制御でこの調整を行うことができるので、構造の簡素化が図れる。
【００７２】
図７に基づいて説明したような音の指向性の度合いを制御する場合においては、位相制御手段１５は、図７の紙面に垂直な方向に並ぶ各列の電気音響変換器２については、入力される被変調信号の位相が列ごとに互いに同じになるように制御してもよく、あるいは、図７の紙面に垂直な方向の列についても表１と同様に位相差を設けるようにしてもよい。後者の制御をした場合には、音の放射角度（広がり角度）を図７の紙面に垂直な方向についても変化させることができる。
【００７３】
また、図７の場合と逆に、各電気音響変換器２に入力される被変調信号の位相が電気音響変換器アレイ１０の中央部から端に向かって順次早まるようにしてもよい。この場合には、各電気音響変換器２からの放射角度が図７と逆になり、放射された超音波が電気音響変換器アレイ１０から離れるにしたがって収束していくような状態とすることができ、基準状態よりも音の指向性が強い状態にすることができる。
【００７４】
以上説明したように、本実施形態のパラメトリックスピーカ１では、音の指向方向や指向性の強弱を調整することができるが、これらの調整に加えて前述したような可聴音発生位置の調整をさらに組み合わせることにより、音声の伝達範囲の方角、広狭、遠近をそれぞれ調整することができる。よって、本実施形態のパラメトリックスピーカ１では、聴取者がいる場所等に応じて、音声の伝達範囲（伝達領域）を極めて多彩に調整することができ、最適な音声の伝達状態が得られる。
【００７５】
本実施形態のパラメトリックスピーカ１では、電気音響変換器アレイ１０における電気音響変換器２の配列ピッチｄは、放射する超音波の波長λより短い長さであるのが好ましい。これにより、パラメトリックスピーカ１では、ホイヘンスの原理で知られているように、波源の重ね合わせにより、発生する音の指向性をより強く（より鋭く）することができる。すなわち、電気音響変換器２の配列ピッチｄが放射される超音波の波長λより短い場合には、隣接する電気音響変換器２から放射される超音波の波面同士が重なり合って、より平面に近い波面が発生する。よって、電気音響変換器アレイ１０から放射される超音波は、広がることなく、より真っ直ぐに進むので、パラメトリックスピーカ１は、発生する音の指向を特に強くすることができる。この場合、λ／ｄの値は、２以上であるのがより好ましく、８以上であるのがさらに好ましい。また、λ／ｄの上限値は特に限定されないが、製造の容易化、製造コスト低減、歩留まり、微細化ルール、配線ルール等を考慮する観点から、通常、λ／ｄの値は、３２以下程度であるのが好ましい。
【００７６】
本実施形態の電気音響変換器アレイ１０では、図１中の横方向の配列ピッチと縦方向の配列ピッチとが共に等しくｄとなっているが、この横方向の配列ピッチと縦方向の配列ピッチとは、互いに異なっていてもよい。また、その場合、横方向の配列ピッチと縦方向の配列ピッチとの一方だけが超音波の波長λより短くされていてもよいが、両方ともが超音波の波長λより短くされているのが好ましい。また、図示の電気音響変換器アレイ１０では、電気音響変換器２の配列ピッチｄが全領域に渡って一定になっているが、このような構成に限らず、局所的に変化してもよい。また、各列（または各行）が互いに半ピッチずつずれて配置されているような並び方であってもよい。
【００７７】
また、本発明における電気音響変換器アレイ１０では、放射する超音波の波長λを直径とする円とほぼ同じかまたはこれより大きい領域に渡って電気音響変換器２が配置されているのが好ましい。すなわち、電気音響変換器アレイ１０の図１中の横方向の寸法をＬ_１、縦方向の寸法をＬ_２としたとき、Ｌ_１≧λ、かつ、Ｌ_２≧λであるのが好ましい。これにより、パラメトリックスピーカ１では、発生する音の指向性をより強く（より鋭く）することができる。
【００７８】
これは、次のような理由によるものである。一般に、音（超音波を含む）は、音を出す面が広くなると指向性を持つようになり、音を出す面が例えば円形の場合には、その直径が波長と同程度以上になると、顕著な指向性を持つ。よって、上記のように、Ｌ_１≧λかつＬ_２≧λとすることにより、電気音響変換器アレイ１０の大きさ、すなわち、超音波を発生する面の広さがλを直径とする円よりも広くなるので、発生する音の指向性をより強くすることができる。この場合、超音波の波長λの２〜８倍の長さを直径とする円と同じかこれより大きい領域に渡って電気音響変換器２が配置されたものであるのがより好ましい。
【００７９】
また、パラメトリックスピーカ１では、発振手段１１の発振周波数ν_２と、電気音響変換器２の共鳴器６の共鳴周波数ν_３とが近傍、または倍音関係の近傍にあるのが好ましい。ここで、ν_２とν_３とが近傍にあるとは、好ましくは０．８≦ν_２／ν_３≦１．２、より好ましくは０．９≦ν_２／ν_３≦１．１なる関係を満足することを言う。また、ν_２とν_３とが倍音関係の近傍にあるとは、ｍおよびｎをそれぞれ正の整数として、ｍ×ν_２と、ｎ×ν_３とが上記と同様に近傍にあることを言う。これにより、振動板２２１で発生した超音波をより強く共鳴させることができるので、電気音響変換器２の変換効率をさらに向上することができる。
【００８０】
また、パラメトリックスピーカ１では、共鳴器６の共鳴周波数ν_３と、振動板２２１の固有振動数ν_１とが近傍、または倍音関係の近傍にあるのが好ましい。ここで、ν_３とν_１とが近傍にあるとは、好ましくは０．８≦ν_３／ν_１≦１．２、より好ましくは０．９≦ν_３／ν_１≦１．１なる関係を満足することを言う。また、ν_３とν_１とが倍音関係の近傍にあるとは、ｉおよびｊをそれぞれ正の整数として、ｉ×ν_３と、ｊ×ν_１とが上記と同様に近傍にあることを言う。これにより、振動板２２１で発生した超音波をより強く共鳴させることができるので、電気音響変換器２の変換効率をさらに向上することができる。
さらに、パラメトリックスピーカ１では、振動板２２１の固有振動数ν_１と、発振手段１１の発振周波数ν_２と、共鳴器６の共鳴周波数ν_３とが互いに近傍にあるか倍音関係の近傍にあるのが最も好ましい。
【００８１】
以上、本発明のパラメトリックスピーカの第１実施形態について説明したが、本発明における電気音響変換器の構成は、前述した電気音響変換器２のような構成のものに限らず、いかなるものでもよく、例えば、以下に説明する第２〜第５実施形態における電気音響変換器２Ａ〜２Ｄのような構成のものであってもよい。なお、下記の第４〜第５実施形態の説明においては、前述した実施形態との相違点を中心に説明し、同様の事項についてはその説明を省略する。
【００８２】
＜第２実施形態＞
図８は、本発明のパラメトリックスピーカの第２実施形態における電気音響変換器を示す断面側面図である。
図８に示す電気音響変換器２Ａは、共鳴器６の放音孔６４が、第１のプレート２１に形成された貫通孔で構成されていること以外は、前記第１実施形態の電気音響変換器２と同様である。この電気音響変換器２Ａでは、放音孔６４は、振動板２２１と対向する位置に形成されている。そして、この放音孔６４から、超音波が図８中の上方向に向けて放射される。また、本実施形態における共鳴器６では、図８中のＬで示す長さがポート部の長さとなる。
【００８３】
＜第３実施形態＞
図９および図１０は、それぞれ、本発明のパラメトリックスピーカの第３実施形態における電気音響変換器を示す斜視図および断面側面図である。なお、以下では、説明の都合上、図９および図１０中の上側を「先端」、下側を「基端」と言う。
【００８４】
図９および図１０に示す電気音響変換器２Ｂは、長尺形状（細長い形状）をなす圧電アクチュエータ（圧電振動体）３と、該圧電アクチュエータ３の基端（固定端）部を支持する基台４と、圧電アクチュエータ３の先端（自由端）側に設置された振動板５と、振動板５が発生する超音波を共鳴させる共鳴器６と、固定部材７５とを備えている。
【００８５】
図９に示すように、本実施形態では、ｎ行×２列（ｎは、２以上の整数）に並ぶ複数の電気音響変換器２Ｂが一体になっており、基台４、振動板５、共鳴器６および固定部材７５（固定部材７５は図９中では省略）は、それぞれ、各電気音響変換器２Ｂのものが一体に形成されている。
図１０に示すように、同図中で左側の列の電気音響変換器２Ｂと右側の列の電気音響変換器２Ｂとは、その構造が互いに面対称の関係にある。また、各列の複数の電気音響変換器２Ｂは、その構造が互いに同じになっている。よって、以下では、１つの電気音響変換器２Ｂについて代表して説明する。
【００８６】
圧電アクチュエータ３は、電気信号（振動電圧）が入力（印加）されることにより、その長手方向に伸縮振動するものである。この圧電アクチュエータ３は、圧電材料と導電材料とをそれぞれ層状に交互に積層した部分を有している。また、本実施形態では、圧電材料と導電材料とは、圧電アクチュエータ３の伸縮方向（長手方向）に対し平行に積層されている。
【００８７】
以下、この圧電アクチュエータ３の製造方法の一例について説明するが、製造工程の図示は省略する。また、以下の例は、列方向（図１０の紙面に垂直な方向）に並ぶ複数の圧電アクチュエータ３を同時に製造する場合の例である。
定盤の上にペースト状に調製した圧電材料（例えばチタン酸・ジルコン酸鉛系複合ペロブスカイトセラミックス材料）を薄く塗布して第１の圧電材料層３１を形成し、これの表面に例えば蒸着または導電性塗料の塗布等の方法により、第１の圧電材料層３１の一部に露出部を残すようにして第１の導電層３２を形成し、さらにこの第１の導電層３２および第１の圧電材料層３１の露出部との表面に圧電材料を薄く塗布して第２の圧電材料層３３を形成し、さらにこれの上に第１の導電層３２とは異なる側に第２の導電層３４を形成する、という工程を必要な回数だけ繰り返す。
【００８８】
このようにして所定の層数を形成した段階で、乾燥させ、これに圧力を加えた状態で温度１０００〜１２００℃で１時間程度焼成することにより板状のセラミック（圧電板）に仕上がる。次いで、各第１の導電層３２が露出している一方の端部に導電塗料を塗布して一方の集電極３５を、また各第２の導電層３４が露出している他方の端部に導電塗料を塗布して集電極３６を形成する。このようにして形成された圧電板を基台４（基台４の集合体）の突部４１に例えば導電性接着剤等を用いて固定し、所定幅間隔で、基台４の表面近傍までダイヤモンドカッタ等によりカット（歯割加工）する。この歯割加工（切削）により生じたスリットによって前記圧電板を複数の長尺形状部材に分離することにより、複数の圧電アクチュエータ３が形成される。圧電アクチュエータ３は、例えば以上説明したような方法により、比較的容易かつ低コストで製造することができる。
【００８９】
このような圧電アクチュエータ３では、複数の第１の導電層３２と、複数の第２の導電層３４とが、一対の櫛歯電極として機能する。そして、電気音響変換器２Ｂでは、集電極３５、３６に、それぞれ、図示しない導電材料（導電部材）が接続されており、一対の櫛歯電極としての第１の導電層３２および第２の導電層３４に電気信号（電圧）を入力（印加）することができるようになっている。なお、振動板５が導電材料で構成されている場合には、振動板５が集電極３５に対する導電部材として機能してもよい。
【００９０】
図１０に示す圧電アクチュエータ３では、圧電材料と導電材料（電極）とが伸縮方向（長手方向）に平行に配置されていることにより、他の振動モードと比較してより高いエネルギー効率が得られる。
圧電アクチュエータ３は、伸縮振動の固有振動数ν_１が、２０ｋＨｚ〜８００ｋＨｚであるのが好ましく、４０ｋＨｚ〜４００ｋＨｚであるのがより好ましい。また、前記と同様に、この固有振動数ν_１と、共鳴器６の共鳴周波数ν_３とが近傍、または倍音関係の近傍にあることがより好ましい。
【００９１】
図１１は、本実施形態における圧電アクチュエータの他の構成例を示す斜視図である。図１１に示す圧電アクチュエータ３Ａでは、圧電材料と導電材料とが圧電アクチュエータ３Ａの伸縮方向（長手方向）に対し垂直に積層されている。本実施形態では、前記圧電アクチュエータ３に代えて、この圧電アクチュエータ３Ａのようなものを用いてもよい。図１１に示す圧電アクチュエータ３Ａでは、圧電材料と導電材料とをより多くの層で積層することができるので、より低い電圧で駆動することができる。
【００９２】
図１０に示すように、基台４は、その基端側の部分に、圧電アクチュエータ３を固定するための側方に突出した突部４１を有している。圧電アクチュエータ３は、その先端（先端面）が振動板５に接合され、その基端部が基台４の突部４１に固定されている。
本実施形態では、圧電アクチュエータ３の基端部が基台４に固着されているため、基台４の強度（剛性）により、圧電アクチュエータ３にはそれほど大きな強度が必要とされないことから、製造が容易であり、小型化にも有利である。また、図示の構成では、圧電アクチュエータ３は、その伸縮方向（長手方向）に平行な面が基台４の突部４１に重なるように固着されている。これにより、上記効果がより顕著に発揮される。
【００９３】
基台４は、その先端の位置が圧電アクチュエータ３の先端面とほぼ一致し、また基端の位置が圧電アクチュエータ３の基端を超えて基端方向に突出する大きさに構成されている。すなわち、圧電アクチュエータ３の伸縮方向についての基台４の長さは、圧電アクチュエータ３の長さより長くなっている。そして、基台４は、その基端（基端面）を固定部材７５に固定されている。また、基台４の先端（先端面）は、振動板５に接合（固定）されている。固定部材７５は、振動板５および共鳴器６を支持するとともに、基台４を介して圧電アクチュエータ３の先端を振動板５に当接させている。
【００９４】
基台４の先端面には、後述する共鳴室６３と圧電アクチュエータ３とを隔離する振動板５が固定されている。この振動板５は、圧電アクチュエータ３の先端面と接合（固定または当接）された振動部５１を有している。また、振動板５は、振動部５１の近傍に設けられた凹部５２、５３によって形成された薄肉部を有している。これにより、振動部５１は、圧電アクチュエータ３の振動により確実に追従して振動できるようになっている。
【００９５】
振動板５の構成材料は、特に限定されないが、例えば、ステンレス鋼、シリコン、エポキシ樹脂、アクリル樹脂、ジグリコールジアルキルカルボネート樹脂、不飽和ポリエステル樹脂、ポリウレタン樹脂、ポリイミド樹脂、メラミン樹脂、フェノール樹脂、尿素樹脂窒化珪素、ジルコニア、部分安定化ジルコニア等の、各種金属材料、各種樹脂材料、各種セラミックを用いることができる。
【００９６】
振動板５の先端面側には、共鳴室６３を有する共鳴器６が設置されている。この共鳴器６は、ヘルムホルツ共鳴器として機能するものである。共鳴器６は、振動板５の先端面側に重ねて接合（固定）されたスペーサプレート（スペーサ部材）６２と、該スペーサプレート６２の先端面側に重ねて接合（固定）された放音プレート６１とで構成されている。
【００９７】
スペーサプレート６２は、振動板５との接合面側に形成された凹部６２１と、凹部６２１から先端面側に貫通する貫通孔６２２とを有している。凹部６２１によって、振動板５と放音プレート６１との間に空間（隙間）が形成されており、この凹部６２１内の空間が共鳴室６３を構成している。
放音プレート６１には、貫通孔６２２を介して共鳴室６３に連通する放音孔６４が形成されている。この放音孔６４および貫通孔６２２は、ヘルムホルツ共鳴器におけるポート部を構成する。
【００９８】
図示の構成では、放音孔６４および貫通孔６２２は、圧電アクチュエータ３の先端面と非対向な位置に形成されている。これにより、放音孔６４の配置位置の自由度を高めることができ、例えば本実施形態のように、各列の放音孔６４を互いに近づけて配置することも可能になる（図９参照）。
このような電気音響変換器２Ｂの圧電アクチュエータ３に前記被変調信号を入力すると、圧電アクチュエータ３は、その長手方向に伸縮振動し、これに伴って振動板５の振動部５１が振動して、超音波を発生する。振動板５で発生した超音波は、共鳴器６で共鳴し、図１０中の上方向に向かって放射される。
【００９９】
基台４、放音プレート６１、スペーサプレート６２、固定部材７５の構成材料は、それぞれ、特に限定されないが、例えば、ステンレス鋼、シリコン、ＳｉＯ_２、ポリイミド、ポリサルフォン、ネガ型またはポジ型の感光性樹脂材料（エポキシ樹脂、アクリル樹脂、ジグリコールジアルキルカルボネート樹脂、不飽和ポリエステル樹脂、ポリウレタン樹脂、ポリイミド樹脂、メラミン樹脂、フェノール樹脂、尿素樹脂など）等の、各種金属材料、各種樹脂材料、各種ガラス、各種セラミックスを用いることができる。
【０１００】
本実施形態の電気音響変換器２Ｂでは、共鳴器６を設けたことにより、超音波を共鳴させて放射することができるので、入力された電気信号を超音波（音響エネルギー）に変換する変換効率が高い。よって、電気音響変換器２Ｂを用いたパラメトリックスピーカでは、比較的低い電圧の電気信号でも十分な強さで超音波を放射することができるので、電力消費量の低減が図れる。
さらに、本実施形態の電気音響変換器２Ｂは、小型化に極めて有利である。よって、比較的小さい電気音響変換器アレイ１０でも、十分な強さの可聴音が得られ、パラメトリックスピーカの小型化・軽量化が図れる。
【０１０１】
また、電気音響変換器２Ｂでは、基台４を介して共鳴器６（振動板５）に対し圧電アクチュエータ３を位置決めできるため、固定部材７５と基台４との相対的な位置関係を調整することにより共鳴器６（振動板５）に対して圧電アクチュエータ３を正確に位置決めすることができる。よって、圧電アクチュエータ３の先端を振動部５１に高い位置精度で当接させることが可能となる。また、基台４に前記圧電板の基端側を固着した状態で歯割加工してから、固定部材７５に位置決めできるため、機械的強度が高い基台４を介して脆弱な圧電アクチュエータ３を位置決めでき、共鳴器６（振動板５）への位置決め時のハンドリングを容易化することができ、さらに基台４と固定部材７５とが別部材として構成できるため、それぞれの目的に合致した材料、つまり基台４には圧電アクチュエータ３からの反力を受け止めるに十分な剛性の高い材料を、また固定部材７５には射出成形等により製造することが可能な高分子材料等を選択することができる。このようなことから、電気音響変換器２Ｂでは、高性能化（高変換効率化）と、製造コストの低減との両立を、高いレベルで達成することができる。
【０１０２】
また、本実施形態では、圧電アクチュエータ３は、前述したような積層構造を有していることにより、比較的低い電圧でも大きな変位量が得られるとともに、制御性（応答性）に優れる。これにより、本実施形態の電気音響変換器２Ｂは、さらに優れた変換効率が得られ、パラメトリックスピーカに用いた場合、より優れた音質が得られる。また、圧電アクチュエータ３は、前述したような積層構造を有していることにより、加工性にも優れ、量産に適し、より低いコストで製造することができ、さらに耐久性も高い。
【０１０３】
＜第４実施形態＞
図１２は、本発明のパラメトリックスピーカの第４実施形態における電気音響変換器を示す斜視図である。図１２に示す電気音響変換器２Ｃでは、前記電気音響変換器２Ｂと異なり、共鳴器６がスペーサプレート６２を有さず、振動板５’に放音プレート６１’が重ねて接合（固定）されている。そして、振動板と放音プレートとの接合面側にそれぞれ形成された凹部５４、５５と凹部６５とにより、共鳴器６の共鳴室６３が形成されている。なお、図示の構成では、凹部５４、５５は、隣り合う電気音響変換器２Ｃのものが連通しているが、共鳴器として独立させるためには、隔壁を形成することにより分離することがより望ましい。図１２に示す実施形態では、スペーサプレート６２が不要となり、組立工程の簡素化が図れる。上記の点以外は、電気音響変換器２Ｃは、前記電気音響変換器２Ｂと同様である。
【０１０４】
＜第５実施形態＞
図１３、図１４および図１５は、それぞれ、本発明のパラメトリックスピーカの第５実施形態における電気音響変換器を示す断面正面図、断面側面図および平面図である。なお、以下では、説明の都合上、図１３および図１４中の上側を「上」、下側を「下」と言う。
【０１０５】
図１５に示すように、本実施形態では、行列状（図１５では２行×６列）に並ぶ複数（１２個）の電気音響変換器２Ｄが一体に形成されている。また、図１５中、上の行の電気音響変換器２Ｄと、下の行の電気音響変換器２Ｄとは、半ピッチずらして配置されている。各電気音響変換器２Ｄは、その構造が互いに同じであるので、以下では、１つの電気音響変換器２Ｄについて代表して説明する。
【０１０６】
図１３および図１４に示すように、電気音響変換器２Ｄは、板状をなす圧電アクチュエータ（圧電振動体）３Ｂと、該圧電アクチュエータ３Ｂと重ねて接合された振動板５Ａと、振動板５Ａが発生する超音波を共鳴させる共鳴器６とを備えている。なお、圧電アクチュエータ３Ｂの第２の電極３９、振動板５Ａおよび共鳴器６は、それぞれ、図１５に示す各電気音響変換器２Ｄのものが一体に形成されている。
【０１０７】
圧電アクチュエータ３Ｂは、板状の圧電素子３７と、該圧電素子３７の下面側に接合された第１の電極３８と、上面側に接合された第２の電極３９とを有している。この圧電アクチュエータ３Ｂは、撓み振動モードのものであり、第１の電極３８と第２の電極３９との間に電気信号（振動電圧）が入力（印加）されることにより、撓み振動する。
【０１０８】
図示の構成では、第１の電極３８は、各電気音響変換器２Ｄに個別に設けられたセグメント電極となっており、第２の電極３９は、各電気音響変換器２Ｄに共通の共通電極となっている。そして、各第１の電極３８には、外に引き出すためのリード部３８１が接続されている。なお、図示の構成と逆に、第１の電極３８が共通電極、第２の電極がセグメント電極となっていてもよい。
【０１０９】
圧電アクチュエータ３Ｂは、撓み振動の固有振動数ν_１が、２０ｋＨｚ〜８００ｋＨｚであるのが好ましく、４０ｋＨｚ〜４００ｋＨｚであるのがより好ましい。また、前記と同様に、この固有振動数ν_１と、共鳴器６の共鳴周波数ν_３とが近傍、または倍音関係の近傍にあることがより好ましい。
このような圧電アクチュエータ３Ｂの第１の電極３８および圧電素子３７は、絶縁層７７に形成された開口部（窓部）内に設けられている。絶縁層７７は、例えば二酸化シリコン（ＳｉＯ_２）、ポリイミド等の絶縁材料で構成されている。第２の電極３９は、絶縁層７７の上面にも連続して形成されている。
【０１１０】
圧電アクチュエータ３Ｂおよび絶縁層７７の下面側には、振動板５Ａが接合（固定）されている。振動板５Ａは、圧電アクチュエータ３Ｂの撓み振動により変形可能な弾性を有する薄板で構成されている。この振動板５Ａは、圧電アクチュエータ３Ｂの撓み振動に伴って弾性変形し、超音波を発生するように振動（撓み振動）する。
振動板５Ａの構成材料は、特に限定されないが、例えば、ステンレス鋼、表面に電気絶縁膜形成処理がなされた不錆鋼、シリコン、エポキシ樹脂、アクリル樹脂、ジグリコールジアルキルカルボネート樹脂、不飽和ポリエステル樹脂、ポリウレタン樹脂、ポリイミド樹脂、メラミン樹脂、フェノール樹脂、尿素樹脂窒化珪素、ジルコニア、部分安定化ジルコニア等の、各種金属材料、各種樹脂材料、各種セラミックを用いることができる。
なお、振動板５Ａを導電性材料で構成し、振動板５Ａに圧電アクチュエータ３Ｂに対する電極としての機能を持たせてもよい。これにより、構造のさらなる簡素化が図れ、さらに容易かつ低コストで製造することができる。
【０１１１】
振動板５Ａの下面側には、共鳴器６が設置されている。この共鳴器６は、共鳴室６３を有し、ヘルムホルツ共鳴器として機能するものである。共鳴器６は、振動板５Ａの下面側に接着剤層７６を介して重ねて接合（固定）されたスペーサプレート６２と、該スペーサプレート６２の下面側に重ねて接合（固定）された放音プレート６１とで構成されている。スペーサプレート６２によって、振動板５Ａと放音プレート６１との間に空間が形成され、この空間が共鳴室６３を構成している。
【０１１２】
スペーサプレート６２の製造方法は、特に限定されないが、例えば、共鳴室６３を形成するのに適した厚さを備えた基板（例えば、単結晶シリコン基板や不錆鋼基板等）を一方の面から他方の面まで貫通するように異方性エッチングや化学エッチングして開口を形成する方法や、グリーンシート状のセラミックスをプレスで成形した後これを焼成する方法により、好適に製造することができる。
放音プレート６１には、共鳴室６３に連通する放音孔６４が形成されている。放音プレート６１は、スペーサプレート６２に対し、例えば接着剤による接着等の方法により気密的に固定されている。この放音孔６４は、ヘルムホルツ共鳴器におけるポート部を構成する。
【０１１３】
このような電気音響変換器２Ｄの圧電アクチュエータ３Ｂに超音波帯域の周波数で電圧が振動する電気信号（前記被変調信号）を入力すると、圧電アクチュエータ３Ｂは、撓み振動し、これに伴って振動板５Ａが厚み方向に振動（撓み振動）して、超音波を発生する。振動板５Ａで発生した超音波は、共鳴器６で共鳴し、図１３および図１４中の下方向に向かって放射される。
【０１１４】
放音プレート６１、スペーサプレート６２の構成材料は、それぞれ、特に限定されないが、例えば、ステンレス鋼、シリコン、ＳｉＯ_２、ポリイミド、ポリサルフォン、ネガ型またはポジ型の感光性樹脂材料（エポキシ樹脂、アクリル樹脂、ジグリコールジアルキルカルボネート樹脂、不飽和ポリエステル樹脂、ポリウレタン樹脂、ポリイミド樹脂、メラミン樹脂、フェノール樹脂、尿素樹脂など）等の、各種金属材料、各種樹脂材料、各種ガラス、各種セラミックスを用いることができる。
【０１１５】
このような電気音響変換器２Ｄは、上述したように板状の各部材を積層することによって製造することができることから、小型化に極めて有利である。
また、電気音響変換器２Ｄは、圧電アクチュエータ３Ｂを撓み振動モードで用いることにより、低電圧での駆動でも変位量が大きく、また、高い制御性が得られる。よって、電気音響変換器２Ｄを用いたパラメトリックスピーカでは、電力消費量の低減を図りつつ、高い音質が得られる。さらに、耐久性、加工性に優れ、量産にも適する。
なお、本実施形態の電気音響変換器では、振動板５Ａがなく、圧電アクチュエータ３Ｂ自体が振動板としても機能するようなものでもよい。
【０１１６】
次に、圧電アクチュエータ３Ｂについて、さらに詳細に説明する。
圧電アクチュエータ３Ｂの圧電素子３７は、第１の電極３８上に、水熱法（水熱合成法）により形成されたものであるのが好ましい。この水熱法では、圧電素子３７は、例えばチタンで構成された第１の電極３８を成長基板として、圧電材料を成長させて層状に形成することができる。なお、水熱法については、例えば、特開平５−１３６４７６号公報、特開平６−２０６７８７号公報、特開平６−３１４８２１号公報等に記載されている。
【０１１７】
圧電素子３７を水熱法によって形成した場合には、第１の電極３８上に圧電素子３７の結晶が成長している構造を備えるため、両者の接合強度が高く、また焼成よりもはるかに低い温度で行うことができるため、熱膨張差に起因する反りの発生や、残留応力の発生がない。また、圧電素子３７は、その成長時間を調整することによって膜厚を制御できるため、極めて薄くかつ均一に形成することができる。この結果、圧電素子３７に作用する電界強度が大きくなり、より低い駆動電圧で大きな撓み振動を生じさせることが可能となる。この場合、圧電素子３７の膜厚は、０．５μｍ〜５０μｍであるのが好ましく、１μｍ〜１０μｍであるのがより好ましい。
【０１１８】
以上、本発明のパラメトリックスピーカを図示の実施形態について説明したが、本発明は、これに限定されるものではなく、パラメトリックスピーカを構成する各部は、同様の機能を発揮し得る任意の構成のものと置換することができる。また、任意の構成物が付加されていてもよい。
また、前述した実施形態では、各電気音響変換器に入力される被変調信号の位相を変化させる複数の移相器を有する位相制御手段を備えたパラメトリックスピーカについて説明したが、本発明のパラメトリックスピーカは、この位相制御手段を有さないものであってもよい。
また、前述した実施形態では、複数の電気音響変換器を並べてなる電気音響変換器アレイを備えたパラメトリックスピーカについて説明したが、本発明のパラメトリックスピーカでは、電気音響変換器の個数は、１個でもよい。
【図面の簡単な説明】
【図１】本発明のパラメトリックスピーカの実施形態における電気音響変換器アレイを示す平面図。
【図２】図１に示す電気音響変換器アレイにおける１つの電気音響変換器を示す断面側面図。
【図３】本発明のパラメトリックスピーカの実施形態を示すブロック図。
【図４】パラメトリックスピーカの原理を説明するための図。
【図５】本発明のパラメトリックスピーカの作用を模式的に示す図。
【図６】図１に示す電気音響変換器アレイの側面図。
【図７】図１に示す電気音響変換器アレイの側面図。
【図８】本発明のパラメトリックスピーカの第２実施形態における電気音響変換器を示す断面側面図。
【図９】本発明のパラメトリックスピーカの第３実施形態における電気音響変換器を示す斜視図。
【図１０】本発明のパラメトリックスピーカの第３実施形態における電気音響変換器を示す断面側面図。
【図１１】第３実施形態における圧電アクチュエータの他の構成例を示す斜視図。
【図１２】本発明のパラメトリックスピーカの第４実施形態における電気音響変換器を示す斜視図。
【図１３】本発明のパラメトリックスピーカの第５実施形態における電気音響変換器を示す断面正面図。
【図１４】本発明のパラメトリックスピーカの第５実施形態における電気音響変換器を示す断面側面図。
【図１５】本発明のパラメトリックスピーカの第５実施形態における電気音響変換器を示す平面図。
【符号の説明】
１……パラメトリックスピーカ １０……電気音響変換器アレイ １０１……配列面 １１……発振手段 １１１……電圧制御発振器 １１２……搬送波発生回路 １２……振幅変調器 １３……増幅器 １４……音声入力インターフェース １５……位相制御手段 １６……移相器 １７……位相制御インターフェース １９……搬送波制御インターフェース ２、２Ａ、２Ｂ、２Ｃ、２Ｄ……電気音響変換器 ２１……第１のプレート ２２……第２のプレート ２２１……振動板 ２３……第３のプレート ２３１……凹部 ２３２……底面 ３、３Ａ、３Ｂ……圧電アクチュエータ ３１……第１の圧電材料層 ３２……第１の導電層 ３３……第２の圧電材料層 ３４……第２の導電層 ３５、３６……集電極 ３７……圧電素子 ３８……第１の電極 ３８１……リード部 ３９……第２の電極 ４……基台 ４１……突部 ５、５’、５Ａ……振動板 ５１……振動部 ５２、５３、５４、５５……凹部 ６……共鳴器 ６１、６１’……放音プレート ６２……スペーサプレート ６２１……凹部 ６２２……貫通孔 ６３……共鳴室 ６４……放音孔 ６５……凹部 ７１……電極 ７２……絶縁層７３、７４……入力端子 ７５……固定部材 ７６……接着剤層 ７７……絶縁層 ２００、３００……波面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to parametric speakers.
[0002]
[Prior art]
A parametric speaker (popularly referred to as an audio spotlight) capable of obtaining high directivity in a direction in which sound is directed is known (for example, see Non-Patent Document 1). The parametric speaker is provided with an electroacoustic transducer that converts an electric signal into an ultrasonic wave and radiates the ultrasonic wave. The ultrasonic wave whose amplitude is modulated according to the audio signal is radiated from the electroacoustic transducer, and the ultrasonic wave is transmitted through the air. An audible sound generated by self-demodulation by a non-linear phenomenon of sound waves during propagation is heard by a human ear. As described above, the parametric speaker can generate an audible sound by emitting an ultrasonic wave having a high directivity, and thus has a relatively high directivity in a direction in which the sound is directed.
As described above, a parametric speaker generates an audible sound by self-demodulating an ultrasonic wave radiated from an electroacoustic transducer while propagating in the air. Therefore, no sound can be heard by human ears at a position closer to the electroacoustic transducer than at a position where the ultrasonic wave self-demodulates and changes to an audible sound.
[0003]
Therefore, when using a parametric speaker, the listener must listen to the sound unless the ultrasonic waves radiated from the electroacoustic transducer are self-demodulated before the listener's position and turned into audible sound. Can not be. Further, if the ultrasonic wave is transmitted to the listener without demodulation, the ultrasonic wave may adversely affect the listener's body.
In order to prevent the above-mentioned inconvenience, the ultrasonic wave may be self-demodulated and changed to an audible sound before the listener's position, but the audible sound is significantly lower than the listener's position. When the sound is generated, the generated sound is attenuated before reaching the listener, and the sound heard by the listener is reduced.
[0004]
[Non-patent document 1]
M. Yoneyama, et al. , J. et al. Acoustic. Soc. Am v73 1532-1536 (1983)
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a parametric speaker that can change the distance from an electroacoustic transducer to a position where an audible sound is generated with a simple structure.
[0006]
[Means for Solving the Problems]
Such an object is achieved by the present invention described below.
Oscillation means for generating a signal whose voltage oscillates at a frequency in the ultrasonic band,
An amplitude modulator that amplitude-modulates a signal generated by the oscillation unit based on an audio signal;
A parametric speaker comprising: at least one electroacoustic transducer that converts a modulated signal modulated by the amplitude modulator into an ultrasonic wave and radiates the air into the air,
The oscillating means has an oscillating frequency variable,
By changing the oscillating frequency of the oscillating means, it is possible to change the distance to the position where the ultrasonic wave radiated from the electro-acoustic transducer self-demodulates and an audible sound is generated.
[0007]
This makes it possible to provide a parametric speaker that can change the distance from the electroacoustic transducer to a position where audible sound is generated with a simple structure. According to this parametric speaker, the efficiency of transmitting sound to the listener can be improved by adjusting the audible sound generation position according to the distance between the electroacoustic transducer array and the listener. In other words, by adjusting the audible sound generation position so that self-demodulation is performed at a position as close as possible to the listener, it is possible to prevent the generated audible sound from attenuating before reaching the listener, and Sound can be transmitted efficiently. Furthermore, by adjusting the audible sound generation position according to the distance between the electroacoustic transducer and the listener, it is possible to prevent the ultrasonic waves from adversely affecting the listener's body.
[0008]
In the parametric speaker of the present invention, as the oscillation frequency is increased, the distance from the electroacoustic transducer to a position where an audible sound is generated is shortened. It is preferable that the distance to the position where the occurrence occurs is long.
Thereby, the distance from the electroacoustic transducer to the position where the audible sound is generated can be controlled easily and with high accuracy.
[0009]
In the parametric speaker according to the present invention, it is preferable that the oscillating means has a voltage controlled oscillator.
Thereby, the distance from the electroacoustic transducer to the position where the audible sound is generated can be controlled easily and with high accuracy.
The parametric speaker of the present invention has an electroacoustic transducer array in which a plurality of the electroacoustic transducers are arranged, and a plurality of phase shifters that change the phase of the modulated signal input to each of the electroacoustic transducers. Phase control means,
It is preferable that the direction of sound can be changed by changing the phase of the modulated signal input to each of the electroacoustic transducers by the phase control means.
This makes it possible to adjust the directional direction of the audible sound to be generated. By combining this with the adjustment of the audible sound generation position, the sound transmission range (transmission area) can be made more versatile according to the location of the listener. , And an optimum voice transmission state can be obtained.
[0010]
In the parametric speaker of the present invention, the phase of the modulated signal input to each of the electro-acoustic transducers is sequentially delayed from one end of the electro-acoustic transducer array toward the other end, thereby producing a sound. It is preferable that the directivity direction can be a direction inclined with respect to the normal direction of the arrangement surface of the electroacoustic transducer.
This makes it possible to control the direction of the audible sound to be generated simply and with high accuracy.
[0011]
The parametric speaker of the present invention has an electroacoustic transducer array in which a plurality of the electroacoustic transducers are arranged, and a plurality of phase shifters that change the phase of the modulated signal input to each of the electroacoustic transducers. Phase control means,
It is preferable that the degree of directivity of sound can be changed by changing the phase of the modulated signal input to each of the electroacoustic transducers by the phase control means.
This makes it possible to adjust the degree (directivity) of the directivity of the generated audible sound. By combining this with the adjustment of the audible sound generation position, the sound transmission range (transmission) can be adjusted according to the location of the listener. Region) can be adjusted more variously, and an optimal voice transmission state can be obtained.
[0012]
In the parametric speaker of the present invention, the phase of the modulated signal input to each of the electro-acoustic transducers is sequentially delayed from the center to the end of the electro-acoustic transducer array, and between adjacent electro-acoustic transducers. It is preferable that the phase difference at the point is gradually increased from the center to the end, so that the sound radiation angle can be increased and the directivity of the sound can be made relatively weak.
This makes it possible to easily and accurately control the degree (strong or weak) of the directivity of the generated audible sound.
[0013]
It is preferable that the parametric speaker of the present invention further includes an amplifier that amplifies the modulated signal input to the electroacoustic transducer.
As a result, a sound with a stronger sound pressure can be generated.
In the parametric speaker of the present invention, the electroacoustic transducer includes:
A piezoelectric actuator that has a long shape and that expands and contracts in its longitudinal direction when the modulated signal is input,
A base supporting a base end of the piezoelectric actuator,
A vibration plate that is installed on the distal end side of the piezoelectric actuator and has a vibration unit that vibrates with expansion and contraction vibration of the piezoelectric actuator, and generates an ultrasonic wave,
A resonator for resonating the generated ultrasonic waves.
As a result, it is possible to configure an electroacoustic transducer array that is excellent in conversion efficiency when converting an electric signal into an ultrasonic wave and is advantageous for miniaturization. As a result, the power consumption of the parametric speaker is reduced, and the size and weight are reduced. Cost can be reduced.
[0014]
In the parametric speaker according to the present invention, it is preferable that the piezoelectric actuator has a portion in which a piezoelectric material and a conductive material are alternately stacked in layers.
Thereby, the piezoelectric actuator of the electroacoustic transducer can obtain a large displacement amount even at a relatively low voltage and can have excellent controllability (responsiveness), so that further excellent conversion efficiency can be obtained. Further, since the workability of the piezoelectric actuator can be improved, it is suitable for mass production and can be manufactured at lower cost.
[0015]
In the parametric speaker of the present invention, the electroacoustic transducer includes:
A piezoelectric actuator that has a plate shape and that bends and vibrates when the modulated signal is input;
Preferably, a resonator for resonating an ultrasonic wave generated by the vibration of the piezoelectric actuator is provided.
As a result, it is possible to configure an electroacoustic transducer array that is excellent in conversion efficiency when converting an electric signal into an ultrasonic wave and is advantageous for miniaturization. As a result, the power consumption of the parametric speaker is reduced, and the size and weight are reduced. Cost can be reduced.
[0016]
In the parametric speaker according to the aspect of the invention, it is preferable that the electroacoustic transducer further includes a diaphragm that is overlapped with and joined to the piezoelectric actuator and that generates an ultrasonic wave by vibrating with bending vibration of the piezoelectric actuator.
Thereby, the conversion efficiency of the electroacoustic transducer can be further improved, and the durability can be further improved.
[0017]
In the parametric speaker of the present invention, the electroacoustic transducer includes:
A diaphragm that vibrates due to the Coulomb force generated by the input of the modulated signal and generates ultrasonic waves,
A resonator for resonating the generated ultrasonic waves.
As a result, it is possible to configure an electroacoustic transducer array that is excellent in conversion efficiency when converting an electric signal into an ultrasonic wave and is advantageous for miniaturization. As a result, the power consumption of the parametric speaker is reduced, and the size and weight are reduced. Cost can be reduced.
[0018]
In the parametric speaker according to the aspect of the invention, the electroacoustic transducer may further include an electrode disposed to face the diaphragm with a gap therebetween, and the Coulomb force acts between the diaphragm and the electrode. Is preferred.
As a result, the structure can be further simplified, and further reduction in size, weight, and cost can be achieved.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a parametric speaker of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
<First embodiment>
FIG. 1 is a plan view showing an electro-acoustic transducer array in a parametric speaker according to an embodiment of the present invention. FIG. 2 is a cross-sectional side view showing one electro-acoustic transducer in the electro-acoustic transducer array shown in FIG. 3 is a block diagram showing an embodiment of the parametric speaker of the present invention, FIG. 4 is a diagram for explaining the principle of the parametric speaker, and FIG. 5 is a diagram schematically showing the operation of the parametric speaker of the present invention. 6 and 7 are side views of the electroacoustic transducer array shown in FIG. 1, respectively.
[0020]
The parametric loudspeaker 1 of the present invention converts a modulated signal obtained by amplitude-modulating a carrier (signal) having a frequency in an ultrasonic band with an audible sound (audio signal) into an ultrasonic wave and radiates it into the air. Is a loudspeaker that can emit highly directional acoustic radiation by demodulating audible sound (self-demodulation).
As shown in FIG. 1, the parametric speaker 1 includes a plurality of electroacoustic transducers 2 that convert the modulated signal into ultrasonic waves and radiate the air into the air (two-dimensionally arranged). It has a transducer array 10. In the electro-acoustic transducer array 10 of the present embodiment, a plurality (many) of electro-acoustic transducers 2 are arranged in a matrix (11 rows × 11 columns in the drawing) at a constant arrangement pitch (arrangement interval) d. It is said that.
[0021]
The illustrated electro-acoustic transducer array 10 has a square shape in plan view, and the respective electro-acoustic transducers 2 are arranged in the square area. However, the shape is not limited to a square, but may be a rectangle, a circle, Any shape such as an ellipse and a polygon may be used.
The number of electroacoustic transducers 2 arranged in the electroacoustic transducer array 10 is not particularly limited, but is preferably at least 16 or more, and more preferably 64 or more.
[0022]
Since the configuration of each electro-acoustic transducer 2 of the electro-acoustic transducer array 10 is similar to each other, the configuration of one electro-acoustic transducer 2 will be described below with reference to FIG. In the description based on FIG. 2, the upper side in FIG. 2 is referred to as “upper” and the lower side is referred to as “lower” for convenience of description.
As shown in FIG. 2, the electroacoustic transducer 2 vibrates (bends) due to Coulomb force (electrostatic force) generated by input of an electric signal (the modulated signal), and generates ultrasonic waves. And a resonator 6 that resonates the ultrasonic waves generated by the diaphragm 221. The resonator 6 has a resonance chamber 63 and a sound emission hole 64 communicating with the resonance chamber 63.
[0023]
The electro-acoustic transducer 2 of the present embodiment includes a first plate (first substrate) 21 also made of silicon, and a second plate (second substrate) 22 made of silicon. On the side, a third plate (third substrate) 23 made of borosilicate glass having a thermal expansion coefficient close to that of silicon has a three-layer structure. Each of these plates is long and continuous in a direction perpendicular to the paper surface of FIG. Each of these plates is provided with a plurality of electroacoustic transducers 2 arranged in a direction perpendicular to the plane of FIG.
[0024]
The constituent materials of the first plate 21, the second plate 22, and the third plate 23 are not limited to those described above, and may be, for example, stainless steel, silicon, SiO ₂ , Polyimide, polysulfone, epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide resin, melamine resin, phenol resin, urea resin silicon nitride, zirconia, partially stabilized zirconia, etc. Metal materials, various resin materials, and various ceramics can be used.
[0025]
The central second plate 22 has a concave portion formed on the joint surface side with the first plate 21. This recess can be formed, for example, by performing an etching process from the surface of the second plate 22. The space inside the recess becomes the resonance chamber 63. That is, the first plate 21 and the second plate 22 define the resonance chamber 63. As described above, the resonator 6 includes the first plate 21 and a part of the second plate 22. The resonance chamber 63 is formed in a rectangular parallelepiped shape that is long in the left-right direction in FIG. This resonator 6 functions as a Helmholtz resonator.
In addition, the second plate 22 has a groove formed from the resonance chamber 63 to the end face of the second plate 22 on the joint surface side with the first plate 21. The groove forms a sound emission hole 64 communicating with the resonance chamber 63. This sound emission hole 64 constitutes a port in the Helmholtz resonator.
[0026]
The bottom wall (bottom) of the portion of the second plate 22 facing the resonance chamber 63 is formed thinner than other portions, and the thin portion forms the diaphragm 221. The diaphragm 221 functions as a diaphragm (diaphragm) that can be elastically deformed (elastically displaced) in the vertical direction in FIG. The volume of the resonance chamber 63 changes due to the vibration (displacement) of the diaphragm 221.
[0027]
The vibration plate 221 has conductivity and also functions as an electrode. In the present embodiment, the diaphragm 221 has conductivity by injecting impurities into the second plate 22 to impart conductivity to the second plate 22 itself. Further, unlike such a configuration, for example, a thin film of a conductive material such as gold or copper may be formed on one surface of the diaphragm 221, in which case, a lower electric resistance (more efficient) (Good) A voltage (charge) can be supplied to the diaphragm 221. This thin film may be formed, for example, by vapor deposition or sputtering.
[0028]
The vibration plate 221 has its natural frequency ν ₁ Is preferably from 20 kHz to 800 kHz, and more preferably from 40 kHz to 400 kHz.
The present invention is not limited to the structure shown in the drawings, but may be a structure that facilitates the vibration plate 221 to vibrate with a larger displacement. For example, a groove (recess) may be formed in a portion of the second plate 22 around the vibration plate 221. Or a structure that supports the diaphragm 221 in a cantilever manner.
[0029]
The third plate 23 has a shallow recess 231 at a position corresponding to the resonance chamber 63 on the side of the joint surface with the second plate 22. The bottom surface (bottom portion) 232 of the concave portion 231 is located facing the diaphragm 221 with a gap therebetween. The recess 231 can be formed by, for example, etching. The internal space of the recess 231 communicates with the outside. Accordingly, it is possible to prevent the pressure in the concave portion 231 from suppressing the vibration of the vibration plate 221.
[0030]
The electrode 71 facing the diaphragm 221 is formed on the bottom surface 232. In addition, the electrode 71 is a segment electrode provided separately for each electroacoustic transducer 2 in the electroacoustic transducer array 10.
The electrode 71 is formed of a silicon oxide film (SiO 2). ₂ ) From above. The insulating layer 72 has a function of protecting the electrode 71 and a function of preventing a short circuit with the diaphragm 221. Note that the insulating layer 72 may be provided on the lower surface of the diaphragm 221.
The electrode 71 and the insulating layer 72 are located between the vibration plate 221 and a gap (gap). Thus, the diaphragm 221 and the electrode 71 constitute a pair of opposing electrodes that oppose each other with the gap and the insulating layer 72 interposed therebetween.
[0031]
On the third plate 23, an input terminal 73 electrically connected to the electrode 71 is formed. The second plate 22 has an input terminal 74 that is electrically connected to the diaphragm 221. In the electroacoustic transducer 2, an electric signal (voltage) can be input (applied) between the diaphragm 221 and the electrode 71 via the input terminals 73 and 74.
As described above, since the second plate 22 itself has conductivity, the diaphragms 221 of the plurality of electroacoustic transducers 2 arranged in a direction perpendicular to the plane of FIG. It serves as an electrode, and can be electrically connected to each of these diaphragms 221 from one input terminal 74.
[0032]
Here, an example of a method for manufacturing the electroacoustic transducer 2 will be described. When the first plate 21 and the second plate 22 are made of silicon, since silicon is a single crystal, anisotropic etching is possible. For example, when the (100) plane is etched, Can be etched regularly. On the (111) plane, etching can be performed in the 90 ° direction. Therefore, by using this characteristic, each part such as the sound emission hole 64 and the resonance chamber 63 can be formed on the first plate 21 or the second plate 22 with high accuracy. Then, on the lower surface side of the second plate 22, a third plate 23 on which an electrode 71 and an insulating layer 72 are formed (a constituent material of the third plate 23 is glass or an insulating material having a thermal expansion coefficient close to that of silicon. It is preferable to use a voltage of, for example, about several hundred volts by using the second plate 22 side as an anode and the third plate 23 side as a cathode, and applying a voltage of, for example, several hundred volts. By performing anodic bonding, the second plate 22 and the third plate 23 can be easily combined with high adhesion. On the upper surface side of the second plate 22, a conductive film used as an electrode in the anodic bonding is formed, and this conductive film can be used as it is as an input terminal 74 to the vibration plate 221. In the present invention, for example, the input terminal 74 may be omitted, and the method of bonding the second plate 22 and the third plate 23 is not limited to anodic bonding.
[0033]
When a voltage is applied between the diaphragm 221 and the electrode 71 of the electroacoustic transducer 2 described above, the diaphragm 221 and the electrode 71 are charged, and an attractive force is generated between the two by the Coulomb force. The diaphragm 221 bends toward the electrode 71 due to this attractive force. In this state, when the application of the voltage to the vibration plate 221 and the electrode 71 is released, the Coulomb force disappears, and the vibration plate 221 is restored by the elastic restoring force upward in FIG. (State shown in FIG. 2) and further displaces upward in FIG.
[0034]
When an electric signal (modulated signal) whose voltage oscillates at a frequency in the ultrasonic band is input between the diaphragm 221 and the electrode 71, the displacement of the diaphragm 221 occurs repeatedly, and the diaphragm 221 is moved. It flexes and vibrates, generating ultrasonic waves. The ultrasonic waves generated by the diaphragm 221 resonate in the resonator 6 and are radiated from the sound output holes 64 toward the left in FIG.
[0035]
In the electro-acoustic transducer 2 of the present embodiment, since the resonator 6 is provided, the ultrasonic wave can be resonated and radiated, so that the conversion efficiency for converting the input electric signal into the ultrasonic wave (acoustic energy). (Hereinafter, sometimes simply referred to as “conversion efficiency”). Therefore, a parametric speaker using the electroacoustic transducer 2 can radiate ultrasonic waves with sufficient intensity even with an electric signal of a relatively low voltage, thereby reducing power consumption.
[0036]
Furthermore, since the electroacoustic transducer 2 can be manufactured by stacking the first plate 21, the second plate 22, and the third plate 23 as described above, it is extremely advantageous for miniaturization. . As will be described later, the electroacoustic transducer array 10 has the electroacoustic transducers 2 arranged at a pitch d shorter than the wavelength λ of the ultrasonic wave to be radiated. Therefore, even the electroacoustic transducer array 10 having the small arrangement pitch d as described above can be easily manufactured. Also, since the number of electroacoustic transducers 2 per unit area of the electroacoustic transducer array 10 can be extremely large, even a relatively small electroacoustic transducer array 10 can have sufficient strength. A hearing sound is obtained, and the size and weight of the parametric speaker 1 can be reduced.
[0037]
In particular, in the present embodiment, the provision of the sound emission holes 64 in the resonator 6 allows the ultrasonic waves to resonate more strongly, achieve even higher conversion efficiency, and radiate the sound pressure of the ultrasonic waves more strongly. Can be. Therefore, the above-described effects (reduction of power consumption, reduction in size and weight) are more remarkably exhibited, and the strength of sound directivity, which is a characteristic of a parametric speaker, can be fully utilized.
[0038]
Note that the resonator 6 preferably satisfies the following conditions in order to obtain a more excellent resonance state. Resonance frequency ν of resonator 6 ₃ Is preferably from 10 kHz to 200 kHz, and more preferably from 20 kHz to 100 kHz. As described later, the resonance frequency ν ₃ Is the natural frequency ν of the diaphragm 221 ₁ And the oscillation frequency ν of the oscillation means 11 of the parametric speaker 1 ₂ It is more preferable that they are close to each other and that they are close to a harmonic relationship. Since the resonator 6 satisfies the above conditions, the effect of the resonator 6 described above is more remarkably exhibited in a parametric speaker using the electroacoustic transducer 2.
In general, a Helmholtz resonator has a resonance frequency ν represented by the following equation.
[0039]
(Equation 1)

In the above equation, c is the speed of sound, S is the opening area of the port (sound emission hole), V is the volume of the resonance chamber, and L is the length of the port (the length indicated by L in FIG. 2). .
[0040]
Hereinafter, based on the above equation, for example, the resonance frequency ν in one embodiment is calculated. Considering a resonator having S = 50 μm × 50 μm, L = 50 μm, and V = 100 μm × 100 μm × 1.5 mm, the resonance frequency ν is about 99 kHz. In this case, in a parametric speaker 1 described later, the oscillation frequency ν near the resonance frequency ν ₂ By using, energy can be transmitted to air with higher efficiency. However, since the actual resonator 6 has a complicated geometric structure, it is desirable that the calculated values as described above are used as a guide, and that the actual values be matched. By doing so, the parametric speaker 1 with lower power (low power consumption) and higher efficiency can be obtained.
[0041]
In addition, since the electroacoustic transducer 2 vibrates (displaces) the diaphragm 221 by Coulomb force (electrostatic force), the displacement amount is large even when driven at a low voltage, and high controllability is obtained. Therefore, in the parametric speaker 1 using the electroacoustic transducer 2, high sound quality can be obtained while reducing power consumption. Furthermore, it has excellent durability and workability, and is suitable for mass production.
[0042]
Hereinafter, an overall configuration of the parametric speaker 1 including the above-described electroacoustic transducer array 10 will be described.
As shown in FIG. 3, the parametric speaker 1 includes an electroacoustic transducer array 10, an oscillating means (carrier generating means) 11, an amplitude modulator (amplitude modulating means) 12, and an electroacoustic transducer 2. It comprises an amplifier (amplifying means) 13, a voice input interface 14, a phase control means 15, a phase control interface 17, and a carrier control interface 19 provided respectively. Although the number of the electroacoustic transducers 2 is 11 in FIG. 3 for convenience of the drawing, the modulated signal is actually input to each electroacoustic transducer 2 of the electroacoustic transducer array 10. You.
[0043]
The oscillating means 11 generates (generates) a signal (carrier) whose voltage oscillates at a frequency in the ultrasonic band (about 20 kHz or more). Oscillation frequency of oscillation means 11 (frequency of carrier wave) ν ₂ Is not particularly limited as long as it is an ultrasonic band, but is preferably about 20 kHz to 400 kHz, and more preferably about 40 kHz to 100 kHz.
[0044]
The oscillating means 11 includes a voltage-controlled oscillator (Voltage Controlled Oscillator) 111 and a carrier generation circuit 112. The voltage controlled oscillator 111 is an oscillator whose oscillation frequency changes with a change in applied voltage. By changing the voltage applied to the voltage controlled oscillator 111, the oscillation frequency of the oscillating means 11 (that is, the frequency of the carrier wave in the parametric speaker 1) ν ₂ Can be changed.
[0045]
A carrier control signal is input to the voltage-controlled oscillator 111 via the carrier control interface 19. The carrier control signal is generated by control means (not shown) included in the parametric speaker 1. The carrier control signal controls the voltage applied to the voltage-controlled oscillator 111, so that the oscillation frequency ν ₂ Control. Note that, in the present invention, unlike such a configuration, the oscillation frequency ν ₂ May be manually adjustable.
[0046]
The voltage controlled oscillator 111 oscillates based on the control by the carrier control signal. The signal oscillated by the voltage controlled oscillator 111 is input to the amplitude modulator 12 via the carrier generation circuit 112.
The carrier generation circuit 112 performs processing such as frequency division and waveform shaping on the signal oscillated by the voltage controlled oscillator 111.
[0047]
The audio signal generated by the audio signal generator (not shown) is input to the amplitude modulator 12 via the audio input interface 14. The amplitude modulator 12 amplitude-modulates a signal oscillated from the oscillating means 11, that is, a carrier, based on the audio signal. The amplitude modulation method in the amplitude modulator 12 is not particularly limited, and may be a normal amplitude modulation method, or may be an envelope modulation method that performs amplitude modulation with the envelope of a signal.
[0048]
The phase control means 15 has a phase shifter (phase shift means) 16 provided for each electroacoustic transducer 2. This phase control means 15 can change the phase of the modulated signal input to each electroacoustic transducer 2 by each phase shifter 16 based on the phase control signal input via the phase control interface 17. . The type of the phase shifter 16 is not particularly limited, and may be electrical or mechanical. Further, the phase shifter 16 may be one that can continuously change the phase or one that changes stepwise.
The phase control signal is generated by control means (not shown) included in the parametric speaker 1.
[0049]
The modulated signal modulated by the amplitude modulator 12 is input to a plurality of phase shifters 16 of the phase control means 15, respectively. The modulated signal that has passed through each phase shifter 16 is input to each amplifier 13 and is amplified to a level at which the electroacoustic transducer 2 can be driven. The modulated signal amplified by each amplifier 13 is input to each electroacoustic transducer 2 of the electroacoustic transducer array 10. Each of the electroacoustic transducers 2 converts the input signal into an ultrasonic wave and radiates the air with directivity in the air. Note that the phase shifter 16 may be provided between the electroacoustic transducer 2 and the amplifier 13 differently from the illustration.
[0050]
Ultrasonic waves (modulated waves) emitted from the electroacoustic transducer array 10 into the air become distorted waves due to the non-linear characteristics of the air, and are demodulated into audible sounds of the original audio signals while propagating through the air. Since the demodulated audible sound has the super directional characteristics of the original ultrasonic wave, the parametric speaker 1 can emit sound only to a desired specific space (specific direction).
[0051]
The principle of the above parametric speaker 1 will be further described with reference to FIG. FIG. 4A shows the waveform of the transmission wave, that is, the audio signal output from the audio signal generator. FIG. 4B shows a waveform of a signal (carrier) generated by the oscillation unit 11. By placing this carrier on the transmission wave, the transmission wave is converted into a modulated wave (modulated signal) as shown in FIG. When the modulated wave is radiated into the air, the sound wave is distorted as shown in FIG. 4D because the air travels faster when the air vibrates in the forward direction and travels slowly when the air travels in the reverse direction due to the nonlinear characteristics of the air. Then, the original audible sound is demodulated (FIG. 4 (e)). This demodulated audible sound has the same directivity as the original ultrasonic wave.
[0052]
In the parametric speaker 1 of the present invention, as described above, the oscillation frequency ν ₂ Is variable, and the oscillation frequency ν ₂ Is changed, the ultrasonic wave radiated from each electro-acoustic transducer 2 (electro-acoustic transducer array 10) self-demodulates and an audible sound is generated (reproduced) (hereinafter referred to as an “audible sound generation position”). You can change the distance to.
Since the ultrasonic waves emitted from the electro-acoustic transducer 2 are gradually attenuated and self-demodulated and change to audible sound, the audible sound generation position is not necessarily strictly determined, but may be defined in this specification. The audible sound generation position refers to a general position at which an audible sound that can be heard substantially by human ears is generated.
[0053]
In the parametric speaker 1 of the present invention, the distance from the electroacoustic transducer 2 to the audible sound generation position can be changed for the following reasons.
According to the knowledge of the present inventor, in the parametric speaker 1, while the ultrasonic wave radiated from each electroacoustic transducer 2 propagates, the shorter the wavelength λ, the faster the attenuation and self-demodulation, and the longer the wavelength λ. The slower the attenuation / self-demodulation is. The frequency of the ultrasonic wave is the oscillation frequency ν of the oscillation unit 11. ₂ Therefore, if the sound speed in the air is c, the wavelength λ is λ = c / ν. ₂ Given by Therefore, in the parametric speaker 1, the oscillation frequency ν ₂ Is increased, the wavelength λ of the ultrasonic wave is shortened, and the distance from each of the electroacoustic transducers 2 (electroacoustic transducer array 10) to the audible sound generation position can be shortened. ₂ Is lower, the wavelength λ of the ultrasonic wave is longer, and the distance from each electro-acoustic transducer 2 (electro-acoustic transducer array 10) to the position where audible sound is generated can be made longer.
[0054]
For example, as shown in (1) of FIG. ₂ Is relatively low f ₁ (For example, about 40 kHz), the distance D from the electroacoustic transducer array 10 to the audible sound generation position ₁ Is relatively long. In this case, the listener is at a distance D from the electroacoustic transducer array 10. ₁ You can hear the sound when you are far away.
On the other hand, as shown in FIG. ₂ Is relatively high f ₂ (For example, about 100 kHz), the distance D from the electroacoustic transducer array 10 to the audible sound generation position ₂ Is relatively short (D ₂ <D ₁ ). In this case, the listener is at a distance D from the electroacoustic transducer array 10. ₂ You can hear the sound when you are far away.
[0055]
In the parametric speaker 1 of the present invention, the distance from the electroacoustic transducer array to the audible sound generation position can be changed as described above. This has the following advantages.
As a first advantage, by adjusting the audible sound generation position according to the distance between the electroacoustic transducer array 10 and the listener, the efficiency of transmitting sound to the listener can be improved. In other words, by adjusting the audible sound generation position so that self-demodulation is performed at a position as close as possible to the listener, it is possible to prevent the generated audible sound from attenuating before reaching the listener, and Sound can be transmitted efficiently.
As a second advantage, by adjusting the audible sound generation position in accordance with the distance between the electroacoustic transducer array 10 and the listener, it is possible to prevent ultrasonic waves from adversely affecting the listener's body.
[0056]
On the other hand, when the audible sound generation position cannot be adjusted as in a conventional parametric speaker, there are the following disadvantages, for example.
First, in a parametric speaker whose audible sound generation position is fixed in the state shown in FIG. 5A, the distance from the electroacoustic transducer array 10 is D. ₁ A shorter distance (eg, D ₂ If there is a listener at a distance of), there is a disadvantage that the listener cannot hear the sound. Also, in this case, the listener is exposed to the ultrasonic waves without attenuation, and the listener is directly exposed to the ultrasonic waves, which may adversely affect the listener's body.
[0057]
Next, in the parametric speaker in which the audible sound generation position is fixed in the state shown in FIG. ₁ Distance D ₂ There is a disadvantage that the audible sound generated at the position is attenuated and reduced before it reaches the listener, resulting in poor hearing.
As described above, when the audible sound generation position cannot be adjusted, if the distance between the electroacoustic transducer array 10 and the listener changes, inconvenience occurs, and it is impossible to cope with the change in the distance.
[0058]
On the other hand, in the present invention, as shown in FIG. ₁ And D ₂ Oscillation frequency ν ₂ To f ₁ And f ₂ In any case, the sound can be transmitted to the listener satisfactorily without causing the above-mentioned inconvenience. That is, in the parametric speaker 1 of the present invention, the audible sound generation position is adjusted according to the change in the distance between the electroacoustic transducer array 10 and the listener, so that the sound transmission to the listener can always be performed well. it can.
[0059]
In the example shown in FIG. 5, the adjustment of the audible sound generation position is performed in two steps, but this is an example, and in the present invention, the adjustment of the audible sound generation position is performed in three or more steps. Alternatively, the audible sound generation position may be adjusted continuously (steplessly). Further, the adjustment of the audible sound generation position may be automatically controlled by providing a sensor for detecting the distance to the listener, or may be adjusted manually.
[0060]
Further, the parametric speaker 1 of the present embodiment changes the phase of the modulated signal input to each electro-acoustic transducer 2 by the phase control means 15 so that the direction of the generated sound and the direction of the generated sound are changed. The degree of sex can be changed (changed).
First, a state in which the phase control unit 15 does not change the phase of the modulated signal input to each of the electroacoustic transducers 2 (a state in which no phase difference occurs between the electroacoustic transducers 2) will be described. Hereinafter, this state is referred to as a reference state.
[0061]
In the reference state, the ultrasonic waves emitted from the electro-acoustic transducer array 10 travel in the normal direction of the array surface 101 of the electro-acoustic transducer 2, so that the direction of the sound generated by the electro-acoustic transducer array 10 is: The direction is the same as the normal direction of the array surface 101.
Note that the arrangement surface 101 refers to a surface (surface direction) on which the electroacoustic transducers 2 are arranged in the electroacoustic transducer array 10.
In the reference state, the ultrasonic wave radiated from the electroacoustic transducer array 10 has a radiation angle (spread angle) close to zero as shown by a dotted line in FIG. But it does not spread outside. Therefore, in the reference state, the degree of directivity of the generated sound is strong.
[0062]
Next, a case where the sound directing direction is set to a direction inclined by an angle θ with respect to the normal direction of the arrangement surface 101 with respect to the above-described reference state will be described with reference to FIG. In this case, the phase control unit 15 determines that the phase of the modulated signal input to each of the electroacoustic transducers 2 is changed from one end (the left side in FIG. 6) of the electroacoustic transducer array 10 to the other end (see FIG. 6 (right side in FIG. 6).
[0063]
Specifically, when the arrangement pitch of the electro-acoustic transducers 2 is d and the wavelength of the ultrasonic wave emitted by the electro-acoustic transducer array 10 is λ, the phase control means 15 is input to each electro-acoustic transducer 2. The phase of the modulated signal is delayed from the left to the right in FIG. 6 by (d · sin θ / λ) × 360 °.
Further, the phase control means 15 controls the electroacoustic transducers 2 in each column arranged in a direction perpendicular to the paper surface of FIG. 6 so that the phase of the input modulated signal is the same for each column.
[0064]
With such a state, the wavefronts 200 of the ultrasonic waves radiated from the respective electroacoustic transducers 2 have the same phase when the positional relationship as shown in FIG. 6 is satisfied. A wavefront 300 inclined by an angle θ with respect to the array plane 101 is generated. Since the ultrasonic waves emitted by the electroacoustic transducer array 10 travel in a direction perpendicular to the wavefront 300, in this state, the sound directing direction is normal to the array surface 101 as shown by a large arrow in FIG. The direction is inclined by an angle θ with respect to the direction.
[0065]
Needless to say, if the direction of sequentially delaying the phase of the modulated signal is reversed, the inclination direction of the sound directing direction can be reversed from that in FIG.
Further, if the direction in which the phase of the modulated signal is sequentially delayed is set to a direction perpendicular to the above, the inclination direction of the sound directing direction can be set to a direction perpendicular to the case of FIG. That is, in the parametric speaker 1, the directional direction of the sound can be inclined in both the vertical direction and the horizontal direction in FIG. Further, by combining the vertical inclination and the horizontal inclination, the directivity direction of the sound can be inclined in the oblique direction in FIG.
[0066]
In this way, in the parametric speaker 1 of the present embodiment, the direction of sound can be changed in any direction without changing the attitude of the electroacoustic transducer array 10. Therefore, even in the case where the sound is directed following the direction in which a person is present, there is no need to provide a mechanism for changing the attitude of the electroacoustic transducer array 10, so that the structure can be simplified.
[0067]
Next, a case where the radiation angle (spread angle) of the sound is increased relative to the reference state and the degree of directivity of the sound is relatively weak will be described with reference to FIG.
Here, as shown in FIG. 7, a case where the radiation angle (spread angle) of the sound is set to 25 ° for each of the left and right sides in FIG. 7 will be described as an example, and the sound speed c in the air will be 350 m. / S, the frequency of the emitted ultrasonic wave is 50 kHz, the wavelength λ is 7 mm, and the arrangement pitch d of the electroacoustic transducer 2 is 3.5 mm. However, it is needless to say that these conditions are not limited to these.
[0068]
In the case shown in FIG. 7, the phase control unit 15 determines that the phase of the modulated signal input to each electroacoustic transducer 2 is sequentially delayed from the center to the end of the electroacoustic transducer array 10 and that the adjacent Control is performed so that the phase difference between the acoustic transducers 2 increases gradually from the center to the end of the electroacoustic transducer array 10.
Specifically, in the state shown in FIG. 7, the phase control means 15 controls the phase of the modulated signal input to each electro-acoustic transducer 2 with respect to the electro-acoustic transducer 2 located at the center, as shown in Table 1 below. Control is performed so as to have the phase delay shown in the rightmost column in the middle. In the following description, in order to distinguish the eleven electroacoustic transducers 2 shown in FIG. 7, for convenience, the numbers 0 to 10 are assigned in order from left to right in FIG. The “number” in Table 1 below is this number.
[0069]
[Table 1]

[0070]
By controlling the phase of the modulated signal input to each electro-acoustic transducer 2 as shown in Table 1, the direction of ultrasonic radiation from the fifth (center) electro-acoustic transducer 2 in FIG. , The direction of radiation from the other electro-acoustic transducers 2 in the normal direction of the arrangement surface 101, and inclining by 5 °, 10 °, 15 °, 20 °, and 25 ° sequentially from the fifth side toward both sides. The angle has to the normal direction of the array surface 101.
[0071]
The phase delay shown in the rightmost column of Table 1 for each electroacoustic transducer 2 can be calculated as follows. First, for each electroacoustic transducer 2, the phase difference between adjacent electroacoustic transducers 2 obtained by (d · sin θ / λ) × 360 ° is calculated, and this is calculated from the fifth electroacoustic transducer 2 on both sides. , The phase lag shown in the rightmost column of Table 1 is obtained (see Table 1).
In this way, in the parametric speaker 1, the degree (strength) of the directivity of the sound can be changed, so that the range in which the sound is directed can be easily adjusted. In addition, since this adjustment can be performed under the control of the phase control means 15, the structure can be simplified.
[0072]
In the case of controlling the degree of directivity of sound as described with reference to FIG. 7, the phase control unit 15 controls the input of the electro-acoustic transducers 2 of each row arranged in a direction perpendicular to the paper surface of FIG. The phase of the modulated signal to be performed may be controlled so as to be the same for each column, or a phase difference may be provided in the column perpendicular to the sheet of FIG. Good. When the latter control is performed, the radiation angle (spread angle) of the sound can be changed in the direction perpendicular to the plane of FIG.
[0073]
Also, contrary to the case of FIG. 7, the phase of the modulated signal input to each electroacoustic transducer 2 may be sequentially advanced from the center to the end of the electroacoustic transducer array 10. In this case, the radiation angle from each of the electroacoustic transducers 2 is opposite to that in FIG. 7, and the emitted ultrasonic waves converge as the distance from the electroacoustic transducer array 10 increases. It is possible to make the sound directivity stronger than the reference state.
[0074]
As described above, in the parametric speaker 1 of the present embodiment, it is possible to adjust the directional direction of sound and the strength of directivity. In addition to these adjustments, the above-described adjustment of the audible sound generation position is further performed. By combining them, it is possible to adjust the direction, wide and narrow, and the distance of the sound transmission range. Therefore, in the parametric speaker 1 of the present embodiment, the sound transmission range (transmission area) can be adjusted in various ways according to the location of the listener and the like, and an optimum sound transmission state can be obtained.
[0075]
In the parametric speaker 1 of the present embodiment, the arrangement pitch d of the electroacoustic transducers 2 in the electroacoustic transducer array 10 is preferably shorter than the wavelength λ of the emitted ultrasonic waves. Thereby, in the parametric speaker 1, the directivity of the generated sound can be made stronger (sharper) by superimposing the wave sources, as is known by the Huygens principle. That is, when the arrangement pitch d of the electroacoustic transducers 2 is shorter than the wavelength λ of the radiated ultrasonic waves, the wavefronts of the ultrasonic waves radiated from the adjacent electroacoustic transducers 2 overlap and are closer to a plane. A wavefront occurs. Therefore, since the ultrasonic waves radiated from the electroacoustic transducer array 10 go straight without spreading, the parametric speaker 1 can make the direction of the generated sound particularly strong. In this case, the value of λ / d is more preferably 2 or more, and further preferably 8 or more. Although the upper limit of λ / d is not particularly limited, the value of λ / d is usually about 32 or less from the viewpoint of facilitation of manufacturing, reduction of manufacturing cost, yield, miniaturization rules, wiring rules, and the like. It is preferred that
[0076]
In the electro-acoustic transducer array 10 of the present embodiment, both the horizontal arrangement pitch and the vertical arrangement pitch in FIG. 1 are equal to d, and the horizontal arrangement pitch and the vertical arrangement pitch are equal. And may be different from each other. Also, in this case, only one of the horizontal arrangement pitch and the vertical arrangement pitch may be shorter than the ultrasonic wavelength λ, but both are shorter than the ultrasonic wavelength λ. preferable. In the illustrated electro-acoustic transducer array 10, the arrangement pitch d of the electro-acoustic transducers 2 is constant over the entire area, but is not limited to such a configuration, and may vary locally. . Further, the arrangement may be such that each column (or each row) is arranged to be shifted from each other by a half pitch.
[0077]
In the electro-acoustic transducer array 10 according to the present invention, it is preferable that the electro-acoustic transducers 2 are arranged over a region that is substantially the same as or larger than a circle whose diameter is the wavelength λ of the emitted ultrasonic wave. . That is, the lateral dimension of the electroacoustic transducer array 10 in FIG. ₁ , The vertical dimension is L ₂ And L ₁ ≧ λ and L ₂ It is preferred that ≧ λ. Thereby, in the parametric speaker 1, the directivity of the generated sound can be made stronger (sharper).
[0078]
This is for the following reason. In general, sound (including ultrasonic waves) has directivity when the surface that emits sound is wide, and when the surface that emits sound is, for example, circular, when its diameter is about the same as or larger than the wavelength, it becomes remarkable. With directivity. Therefore, as described above, L ₁ ≧ λ and L ₂ By setting ≧ λ, the size of the electroacoustic transducer array 10, that is, the area of the surface for generating the ultrasonic wave becomes wider than the circle having the diameter of λ, so that the directivity of the generated sound is further strengthened. can do. In this case, it is more preferable that the electroacoustic transducer 2 is arranged over a region having a diameter equal to or larger than a circle having a length of 2 to 8 times the wavelength λ of the ultrasonic wave.
[0079]
In the parametric speaker 1, the oscillation frequency ν of the oscillation means 11 ₂ And the resonance frequency ν of the resonator 6 of the electroacoustic transducer 2 ₃ Are preferably in the vicinity or in the vicinity of the harmonic relationship. Where ν ₂ And ν ₃ Is in the vicinity, preferably 0.8 ≦ ν ₂ / Ν ₃ ≦ 1.2, more preferably 0.9 ≦ ν ₂ / Ν ₃ It satisfies the relationship of ≦ 1.1. Also, ν ₂ And ν ₃ Is in the vicinity of the harmonic relation, where m and n are each a positive integer and m × ν ₂ And n × ν ₃ Are in the vicinity in the same manner as described above. This allows the ultrasonic waves generated by the diaphragm 221 to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer 2 can be further improved.
[0080]
In the parametric speaker 1, the resonance frequency ν of the resonator 6 ₃ And the natural frequency ν of the diaphragm 221 ₁ Are preferably in the vicinity or in the vicinity of the harmonic relationship. Where ν ₃ And ν ₁ Is in the vicinity, preferably 0.8 ≦ ν ₃ / Ν ₁ ≦ 1.2, more preferably 0.9 ≦ ν ₃ / Ν ₁ It satisfies the relationship of ≦ 1.1. Also, ν ₃ And ν ₁ Means that i and j are positive integers, respectively, i × ν ₃ And j × ν ₁ Are in the vicinity in the same manner as described above. This allows the ultrasonic waves generated by the diaphragm 221 to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer 2 can be further improved.
Further, in the parametric speaker 1, the natural frequency ν of the diaphragm 221 ₁ And the oscillation frequency ν of the oscillation means 11 ₂ And the resonance frequency ν of the resonator 6 ₃ Are most preferably in the vicinity of each other or in a harmonic relationship.
[0081]
Although the first embodiment of the parametric speaker of the present invention has been described above, the configuration of the electro-acoustic transducer of the present invention is not limited to the configuration of the electro-acoustic transducer 2 described above, and may be any configuration. For example, a configuration like the electroacoustic transducers 2A to 2D in the second to fifth embodiments described below may be used. In the following description of the fourth and fifth embodiments, differences from the above-described embodiment will be mainly described, and description of similar items will be omitted.
[0082]
<Second embodiment>
FIG. 8 is a cross-sectional side view showing an electroacoustic transducer according to a second embodiment of the parametric speaker of the present invention.
The electro-acoustic transducer 2A shown in FIG. 8 has the same configuration as the electro-acoustic transducer of the first embodiment except that the sound emission hole 64 of the resonator 6 is formed by a through hole formed in the first plate 21. It is the same as the container 2. In this electroacoustic transducer 2A, the sound emission hole 64 is formed at a position facing the diaphragm 221. Then, ultrasonic waves are emitted from the sound emission holes 64 in the upward direction in FIG. Further, in the resonator 6 according to the present embodiment, the length indicated by L in FIG. 8 is the length of the port portion.
[0083]
<Third embodiment>
9 and 10 are a perspective view and a sectional side view, respectively, showing an electroacoustic transducer in a third embodiment of the parametric speaker of the present invention. In the following, for convenience of explanation, the upper side in FIGS. 9 and 10 is referred to as “distal end”, and the lower side is referred to as “proximal end”.
[0084]
An electroacoustic transducer 2B shown in FIGS. 9 and 10 has a piezoelectric actuator (piezoelectric vibrating body) 3 having a long shape (an elongated shape) and a base supporting a base end (fixed end) of the piezoelectric actuator 3. 4, a vibrating plate 5 installed on the tip (free end) side of the piezoelectric actuator 3, a resonator 6 for resonating the ultrasonic waves generated by the vibrating plate 5, and a fixing member 75.
[0085]
As shown in FIG. 9, in the present embodiment, a plurality of electroacoustic transducers 2B arranged in n rows × 2 columns (n is an integer of 2 or more) are integrated, and a base 4, a diaphragm 5, As for the resonator 6 and the fixing member 75 (the fixing member 75 is omitted in FIG. 9), each of the electroacoustic transducers 2B is integrally formed.
As shown in FIG. 10, the electro-acoustic transducers 2B in the left column and the electro-acoustic transducers 2B in the right column have a plane-symmetric relationship with each other. The plurality of electroacoustic transducers 2B in each row have the same structure. Therefore, hereinafter, one electroacoustic transducer 2B will be described as a representative.
[0086]
The piezoelectric actuator 3 expands and contracts in the longitudinal direction when an electric signal (oscillation voltage) is input (applied). The piezoelectric actuator 3 has a portion in which a piezoelectric material and a conductive material are alternately stacked in layers. Further, in the present embodiment, the piezoelectric material and the conductive material are stacked in parallel with the expansion and contraction direction (longitudinal direction) of the piezoelectric actuator 3.
[0087]
Hereinafter, an example of a method of manufacturing the piezoelectric actuator 3 will be described, but illustration of the manufacturing process is omitted. Further, the following example is an example in which a plurality of piezoelectric actuators 3 arranged in a column direction (a direction perpendicular to the plane of FIG. 10) are manufactured at the same time.
A first piezoelectric material layer 31 is formed by applying a thin paste of a piezoelectric material (for example, a lead titanate / zirconate-based composite perovskite ceramic material) on a surface plate to form a first piezoelectric material layer 31. The first conductive layer 32 is formed so as to leave an exposed portion in a part of the first piezoelectric material layer 31 by a method such as application of a conductive paint, and further, the first conductive layer 32 and the first piezoelectric layer 32 are formed. A second piezoelectric material layer 33 is formed by applying a thin piezoelectric material on the surface of the exposed portion of the material layer 31 to form a second piezoelectric material layer 33, and a second conductive layer 34 is provided on a different side from the first conductive layer 32. Is repeated as many times as necessary.
[0088]
At the stage where a predetermined number of layers are formed in this way, the plate is dried and baked at a temperature of 1000 to 1200 ° C. for about 1 hour in a state where pressure is applied, thereby completing a plate-shaped ceramic (piezoelectric plate). Next, a conductive paint is applied to one end where each first conductive layer 32 is exposed, and one collector electrode 35 is applied to the other end where each second conductive layer 34 is exposed. The collector 36 is formed by applying a conductive paint. The piezoelectric plate thus formed is fixed to the protrusion 41 of the base 4 (an aggregate of the base 4) using, for example, a conductive adhesive or the like, and is spaced from the surface of the base 4 at a predetermined width interval. Cut (tooth cutting) with a diamond cutter or the like. A plurality of piezoelectric actuators 3 are formed by separating the piezoelectric plate into a plurality of elongated members by slits generated by the tooth cutting (cutting). The piezoelectric actuator 3 can be manufactured relatively easily and at low cost, for example, by the method described above.
[0089]
In such a piezoelectric actuator 3, the plurality of first conductive layers 32 and the plurality of second conductive layers 34 function as a pair of comb electrodes. In the electroacoustic transducer 2B, a not-shown conductive material (conductive member) is connected to each of the collecting electrodes 35 and 36, and the first conductive layer 32 and the second conductive layer as a pair of comb-tooth electrodes are provided. An electric signal (voltage) can be input (applied) to the layer 34. When diaphragm 5 is made of a conductive material, diaphragm 5 may function as a conductive member for collector 35.
[0090]
In the piezoelectric actuator 3 shown in FIG. 10, since the piezoelectric material and the conductive material (electrode) are arranged parallel to the expansion and contraction direction (longitudinal direction), higher energy efficiency can be obtained as compared with other vibration modes. .
The piezoelectric actuator 3 has a natural frequency ν of stretching vibration. ₁ Is preferably from 20 kHz to 800 kHz, and more preferably from 40 kHz to 400 kHz. As described above, the natural frequency ν ₁ And the resonance frequency ν of the resonator 6 ₃ Is more preferably in the vicinity or in the vicinity of the overtone relationship.
[0091]
FIG. 11 is a perspective view illustrating another configuration example of the piezoelectric actuator according to the present embodiment. In the piezoelectric actuator 3A shown in FIG. 11, a piezoelectric material and a conductive material are stacked perpendicularly to the expansion / contraction direction (longitudinal direction) of the piezoelectric actuator 3A. In the present embodiment, a piezoelectric actuator 3A may be used instead of the piezoelectric actuator 3. In the piezoelectric actuator 3A shown in FIG. 11, the piezoelectric material and the conductive material can be stacked in more layers, so that they can be driven at a lower voltage.
[0092]
As shown in FIG. 10, the base 4 has a protrusion 41 protruding laterally for fixing the piezoelectric actuator 3 on a base end portion thereof. The piezoelectric actuator 3 has a distal end (distal end surface) joined to the diaphragm 5 and a base end fixed to the protrusion 41 of the base 4.
In this embodiment, since the base end of the piezoelectric actuator 3 is fixed to the base 4, the strength (rigidity) of the base 4 does not require a large strength for the piezoelectric actuator 3. It is easy and advantageous for miniaturization. Further, in the illustrated configuration, the piezoelectric actuator 3 is fixed so that a surface parallel to the expansion and contraction direction (longitudinal direction) overlaps the projection 41 of the base 4. Thereby, the above effect is more remarkably exhibited.
[0093]
The base 4 has such a size that the position of the distal end substantially coincides with the distal end surface of the piezoelectric actuator 3 and the position of the proximal end protrudes in the proximal direction beyond the proximal end of the piezoelectric actuator 3. That is, the length of the base 4 in the expansion and contraction direction of the piezoelectric actuator 3 is longer than the length of the piezoelectric actuator 3. The base end (base end face) of the base 4 is fixed to the fixing member 75. The tip (tip face) of the base 4 is joined (fixed) to the diaphragm 5. The fixing member 75 supports the diaphragm 5 and the resonator 6, and makes the distal end of the piezoelectric actuator 3 abut on the diaphragm 5 via the base 4.
[0094]
A vibration plate 5 for isolating a resonance chamber 63 and a piezoelectric actuator 3, which will be described later, is fixed to the distal end surface of the base 4. The vibrating plate 5 has a vibrating portion 51 that is joined (fixed or abutted) to the distal end surface of the piezoelectric actuator 3. Further, the diaphragm 5 has a thin portion formed by concave portions 52 and 53 provided near the vibrating portion 51. Thus, the vibrating section 51 can reliably follow and vibrate according to the vibration of the piezoelectric actuator 3.
[0095]
Although the constituent material of the diaphragm 5 is not particularly limited, for example, stainless steel, silicon, epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide resin, melamine resin, phenol resin, Various metal materials, various resin materials, and various ceramics such as urea resin silicon nitride, zirconia, and partially stabilized zirconia can be used.
[0096]
A resonator 6 having a resonance chamber 63 is provided on the distal end face side of the diaphragm 5. This resonator 6 functions as a Helmholtz resonator. The resonator 6 includes a spacer plate (spacer member) 62 that is overlapped and fixed (fixed) on the distal end surface side of the diaphragm 5 and a sound emission plate that is overlapped and bonded (fixed) on the distal end surface side of the spacer plate 62. 61.
[0097]
The spacer plate 62 has a concave portion 621 formed on the joint surface side with the vibration plate 5 and a through hole 622 penetrating from the concave portion 621 to the distal end surface side. A space (gap) is formed between the vibration plate 5 and the sound emission plate 61 by the recess 621, and the space in the recess 621 forms the resonance chamber 63.
The sound emission plate 61 is provided with a sound emission hole 64 communicating with the resonance chamber 63 via the through hole 622. The sound emission hole 64 and the through hole 622 constitute a port in the Helmholtz resonator.
[0098]
In the illustrated configuration, the sound emission hole 64 and the through hole 622 are formed at positions not facing the distal end surface of the piezoelectric actuator 3. Thereby, the degree of freedom of the arrangement position of the sound emission holes 64 can be increased, and for example, as in the present embodiment, the sound emission holes 64 in each row can be arranged close to each other (see FIG. 9). .
When the modulated signal is input to the piezoelectric actuator 3 of such an electroacoustic transducer 2B, the piezoelectric actuator 3 expands and contracts in its longitudinal direction, and the vibrating portion 51 of the diaphragm 5 vibrates accordingly. Generates ultrasonic waves. The ultrasonic waves generated by the diaphragm 5 resonate in the resonator 6 and are emitted upward in FIG.
[0099]
The constituent materials of the base 4, the sound emission plate 61, the spacer plate 62, and the fixing member 75 are not particularly limited, but are, for example, stainless steel, silicon, SiO ₂ , Polyimide, polysulfone, negative or positive photosensitive resin materials (epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide resin, melamine resin, phenol resin, urea resin, etc.) For example, various metal materials, various resin materials, various glasses, and various ceramics can be used.
[0100]
In the electro-acoustic transducer 2B of the present embodiment, since the resonator 6 is provided, the ultrasonic wave can be resonated and emitted, so that the conversion efficiency of converting the input electric signal into the ultrasonic wave (acoustic energy). Is high. Therefore, a parametric speaker using the electroacoustic transducer 2B can emit ultrasonic waves with sufficient strength even with an electric signal of a relatively low voltage, so that power consumption can be reduced.
Furthermore, the electro-acoustic transducer 2B of the present embodiment is extremely advantageous for miniaturization. Therefore, even with a relatively small electroacoustic transducer array 10, audible sound of sufficient intensity can be obtained, and the size and weight of the parametric speaker can be reduced.
[0101]
In the electroacoustic transducer 2B, since the piezoelectric actuator 3 can be positioned with respect to the resonator 6 (diaphragm 5) via the base 4, the relative positional relationship between the fixing member 75 and the base 4 is adjusted. Thus, the piezoelectric actuator 3 can be accurately positioned with respect to the resonator 6 (diaphragm 5). Therefore, the tip of the piezoelectric actuator 3 can be brought into contact with the vibrating portion 51 with high positional accuracy. In addition, since the base plate 4 is fixed to the fixing member 75 after the base plate 4 is fixed to the base end side of the piezoelectric plate, the fragile piezoelectric actuator 3 can be positioned via the base 4 having high mechanical strength. Since positioning can be performed, handling at the time of positioning on the resonator 6 (diaphragm 5) can be facilitated, and the base 4 and the fixing member 75 can be configured as separate members, so that materials suitable for each purpose can be used. That is, a material having high rigidity enough to receive the reaction force from the piezoelectric actuator 3 can be selected for the base 4, and a polymer material or the like that can be manufactured by injection molding or the like can be selected for the fixing member 75. . Thus, in the electroacoustic transducer 2B, it is possible to achieve both high performance (high conversion efficiency) and reduction in manufacturing cost at a high level.
[0102]
In the present embodiment, the piezoelectric actuator 3 has the above-described laminated structure, so that a large displacement can be obtained even at a relatively low voltage, and the controllability (response) is excellent. As a result, the electroacoustic transducer 2B of the present embodiment can obtain more excellent conversion efficiency, and can obtain more excellent sound quality when used for a parametric speaker. Further, since the piezoelectric actuator 3 has the above-described laminated structure, it has excellent workability, is suitable for mass production, can be manufactured at lower cost, and has high durability.
[0103]
<Fourth embodiment>
FIG. 12 is a perspective view showing an electroacoustic transducer according to a fourth embodiment of the parametric speaker of the present invention. In the electro-acoustic transducer 2C shown in FIG. 12, unlike the electro-acoustic transducer 2B, the resonator 6 does not have the spacer plate 62, and the sound emitting plate 61 'is overlapped and joined (fixed) to the diaphragm 5'. ing. Resonance chamber 63 of resonator 6 is formed by concave portions 54 and 55 and concave portion 65 formed on the joint surface side between the diaphragm and the sound emission plate, respectively. In the illustrated configuration, the recesses 54 and 55 communicate with those of the adjacent electroacoustic transducer 2C. However, in order to make the recesses 54 and 55 independent as a resonator, it is more preferable to separate them by forming a partition wall. . In the embodiment shown in FIG. 12, the spacer plate 62 becomes unnecessary, and the assembly process can be simplified. Except for the above, the electroacoustic transducer 2C is the same as the electroacoustic transducer 2B.
[0104]
<Fifth embodiment>
FIGS. 13, 14, and 15 are a cross-sectional front view, a cross-sectional side view, and a plan view, respectively, illustrating an electroacoustic transducer according to a fifth embodiment of the parametric speaker of the present invention. In the following, for convenience of description, the upper side in FIGS. 13 and 14 is referred to as “upper”, and the lower side is referred to as “lower”.
[0105]
As shown in FIG. 15, in the present embodiment, a plurality (12) of electroacoustic transducers 2D arranged in a matrix (2 rows × 6 columns in FIG. 15) are integrally formed. In FIG. 15, the electro-acoustic transducer 2D in the upper row and the electro-acoustic transducer 2D in the lower row are arranged so as to be shifted by a half pitch. Since each electroacoustic transducer 2D has the same structure, only one electroacoustic transducer 2D will be described below as a representative.
[0106]
As shown in FIGS. 13 and 14, the electroacoustic transducer 2D includes a plate-shaped piezoelectric actuator (piezoelectric vibrating body) 3B, a vibrating plate 5A superposed and joined to the piezoelectric actuator 3B, and a vibrating plate 5A. A resonator 6 for resonating the generated ultrasonic waves. As the second electrode 39, the diaphragm 5A, and the resonator 6 of the piezoelectric actuator 3B, those of the respective electroacoustic transducers 2D shown in FIG. 15 are integrally formed.
[0107]
The piezoelectric actuator 3B includes a plate-shaped piezoelectric element 37, a first electrode 38 joined to the lower surface of the piezoelectric element 37, and a second electrode 39 joined to the upper surface. The piezoelectric actuator 3B is of a flexural vibration mode, and flexibly vibrates when an electric signal (vibration voltage) is input (applied) between the first electrode 38 and the second electrode 39.
[0108]
In the illustrated configuration, the first electrode 38 is a segment electrode provided separately for each electro-acoustic transducer 2D, and the second electrode 39 is a common electrode common to each electro-acoustic transducer 2D. Has become. Each of the first electrodes 38 is connected to a lead portion 381 for drawing out. The first electrode 38 may be a common electrode and the second electrode may be a segment electrode, contrary to the illustrated configuration.
[0109]
The piezoelectric actuator 3B has a natural frequency ν of flexural vibration. ₁ Is preferably from 20 kHz to 800 kHz, and more preferably from 40 kHz to 400 kHz. As described above, the natural frequency ν ₁ And the resonance frequency ν of the resonator 6 ₃ Is more preferably in the vicinity or in the vicinity of the overtone relationship.
The first electrode 38 and the piezoelectric element 37 of such a piezoelectric actuator 3B are provided in an opening (window) formed in the insulating layer 77. The insulating layer 77 is made of, for example, silicon dioxide (SiO 2). ₂ ), And an insulating material such as polyimide. The second electrode 39 is also formed continuously on the upper surface of the insulating layer 77.
[0110]
The diaphragm 5A is joined (fixed) to the lower surfaces of the piezoelectric actuator 3B and the insulating layer 77. The vibration plate 5A is formed of a thin plate having elasticity that can be deformed by bending vibration of the piezoelectric actuator 3B. The diaphragm 5A is elastically deformed in accordance with the bending vibration of the piezoelectric actuator 3B, and vibrates (bending vibration) so as to generate ultrasonic waves.
The constituent material of the vibration plate 5A is not particularly limited, but is, for example, stainless steel, non-rusted steel having an electric insulating film formed on its surface, silicon, epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, and unsaturated polyester. Various metal materials, various resin materials, and various ceramics such as resin, polyurethane resin, polyimide resin, melamine resin, phenol resin, urea resin, silicon nitride, zirconia, and partially stabilized zirconia can be used.
The vibration plate 5A may be made of a conductive material, and the vibration plate 5A may have a function as an electrode for the piezoelectric actuator 3B. As a result, the structure can be further simplified, and the device can be manufactured more easily and at lower cost.
[0111]
A resonator 6 is provided on the lower surface side of the diaphragm 5A. The resonator 6 has a resonance chamber 63 and functions as a Helmholtz resonator. The resonator 6 includes a spacer plate 62 overlapped and joined (fixed) to the lower surface of the diaphragm 5A via an adhesive layer 76, and a sound emission overlapped and joined (fixed) to the lower surface of the spacer plate 62. And a plate 61. A space is formed between the diaphragm 5A and the sound emission plate 61 by the spacer plate 62, and this space forms the resonance chamber 63.
[0112]
The method of manufacturing the spacer plate 62 is not particularly limited. For example, a substrate having a thickness suitable for forming the resonance chamber 63 (for example, a single-crystal silicon substrate or a non-rusting steel substrate) is formed on one side. It can be suitably manufactured by a method in which an opening is formed by anisotropic etching or chemical etching so as to penetrate to the other surface, or a method in which a green sheet-shaped ceramic is formed by pressing and firing.
The sound emitting plate 61 is provided with a sound emitting hole 64 communicating with the resonance chamber 63. The sound emission plate 61 is air-tightly fixed to the spacer plate 62 by, for example, bonding with an adhesive. This sound emission hole 64 constitutes a port in the Helmholtz resonator.
[0113]
When an electric signal (modulated signal) whose voltage oscillates at a frequency in the ultrasonic band is input to the piezoelectric actuator 3B of such an electroacoustic transducer 2D, the piezoelectric actuator 3B bends and vibrates. 5A vibrates in the thickness direction (flexural vibration) to generate ultrasonic waves. The ultrasonic waves generated by the diaphragm 5A resonate in the resonator 6, and are radiated downward in FIGS.
[0114]
Although the constituent materials of the sound emitting plate 61 and the spacer plate 62 are not particularly limited, for example, stainless steel, silicon, SiO ₂ , Polyimide, polysulfone, negative or positive photosensitive resin materials (epoxy resin, acrylic resin, diglycol dialkyl carbonate resin, unsaturated polyester resin, polyurethane resin, polyimide resin, melamine resin, phenol resin, urea resin, etc.) For example, various metal materials, various resin materials, various glasses, and various ceramics can be used.
[0115]
Such an electroacoustic transducer 2D can be manufactured by laminating each plate-shaped member as described above, which is extremely advantageous for miniaturization.
Further, in the electro-acoustic transducer 2D, by using the piezoelectric actuator 3B in the bending vibration mode, the displacement is large even when driven at a low voltage, and high controllability is obtained. Therefore, in a parametric speaker using the electroacoustic transducer 2D, high sound quality can be obtained while reducing power consumption. Furthermore, it has excellent durability and workability, and is suitable for mass production.
In the electro-acoustic transducer according to the present embodiment, the piezoelectric actuator 3B itself may function as a diaphragm without the diaphragm 5A.
[0116]
Next, the piezoelectric actuator 3B will be described in more detail.
The piezoelectric element 37 of the piezoelectric actuator 3B is preferably formed on the first electrode 38 by a hydrothermal method (hydrothermal synthesis method). In this hydrothermal method, the piezoelectric element 37 can be formed in a layer shape by growing a piezoelectric material using the first electrode 38 made of, for example, titanium as a growth substrate. The hydrothermal method is described in, for example, JP-A-5-136476, JP-A-6-206787, and JP-A-6-314821.
[0117]
When the piezoelectric element 37 is formed by a hydrothermal method, a structure in which the crystal of the piezoelectric element 37 is grown on the first electrode 38 is provided, so that the bonding strength between the two is high, and the bonding strength is much lower than firing. Since it can be performed at a temperature, there is no warpage or residual stress due to the difference in thermal expansion. In addition, the thickness of the piezoelectric element 37 can be controlled by adjusting the growth time, so that the piezoelectric element 37 can be formed to be extremely thin and uniform. As a result, the strength of the electric field acting on the piezoelectric element 37 is increased, and it becomes possible to generate large flexural vibration at a lower driving voltage. In this case, the thickness of the piezoelectric element 37 is preferably 0.5 μm to 50 μm, and more preferably 1 μm to 10 μm.
[0118]
As described above, the parametric speaker of the present invention has been described with respect to the illustrated embodiment. However, the present invention is not limited to this, and each part constituting the parametric speaker has an arbitrary configuration capable of exhibiting the same function. Can be replaced by Further, an arbitrary component may be added.
Further, in the above-described embodiment, the parametric speaker including the phase control unit having the plurality of phase shifters that changes the phase of the modulated signal input to each electroacoustic transducer has been described. May not have this phase control means.
In the above-described embodiment, a parametric speaker including an electroacoustic transducer array in which a plurality of electroacoustic transducers are arranged has been described. However, in the parametric speaker of the present invention, the number of electroacoustic transducers is one. Good.
[Brief description of the drawings]
FIG. 1 is a plan view showing an electroacoustic transducer array in a parametric speaker according to an embodiment of the present invention.
FIG. 2 is a sectional side view showing one electro-acoustic transducer in the electro-acoustic transducer array shown in FIG.
FIG. 3 is a block diagram showing an embodiment of a parametric speaker of the present invention.
FIG. 4 is a diagram illustrating the principle of a parametric speaker.
FIG. 5 is a diagram schematically showing the operation of the parametric speaker of the present invention.
FIG. 6 is a side view of the electroacoustic transducer array shown in FIG. 1;
FIG. 7 is a side view of the electroacoustic transducer array shown in FIG. 1;
FIG. 8 is a cross-sectional side view showing an electroacoustic transducer in a second embodiment of the parametric speaker of the present invention.
FIG. 9 is a perspective view showing an electroacoustic transducer according to a third embodiment of the parametric speaker of the present invention.
FIG. 10 is a sectional side view showing an electroacoustic transducer in a third embodiment of the parametric speaker of the present invention.
FIG. 11 is a perspective view showing another configuration example of the piezoelectric actuator according to the third embodiment.
FIG. 12 is a perspective view showing an electroacoustic transducer according to a fourth embodiment of the parametric speaker of the present invention.
FIG. 13 is a sectional front view showing an electroacoustic transducer in a fifth embodiment of the parametric speaker of the present invention.
FIG. 14 is a sectional side view showing an electroacoustic transducer in a fifth embodiment of the parametric speaker of the present invention.
FIG. 15 is a plan view showing an electroacoustic transducer according to a fifth embodiment of the parametric speaker of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Parametric speaker 10 ... Electroacoustic transducer array 101 ... Array surface 11 ... Oscillating means 111 ... Voltage controlled oscillator 112 ... Carrier wave generation circuit 12 ... Amplitude modulator 13 ... Amplifier 14 ... Audio input Interface 15 Phase control means 16 Phase shifter 17 Phase control interface 19 Carrier control interface 2, 2A, 2B, 2C, 2D Electroacoustic transducer 21 First plate 22 Second plate 221 Vibrating plate 23 Third plate 231 Recess 232 Bottom surface 3, 3A, 3B Piezoelectric actuator 31 First piezoelectric material layer 32 First conductive layer 33 second piezoelectric material layer 34 second conductive layer 35, 36 collector electrode 37 piezoelectric element 38 first electrode 381 lead Part 39... Second electrode 4... Base 41... Protrusion 5, 5 ′, 5 A... 61 '... sound emission plate 62 ... spacer plate 621 ... recess 622 ... through hole 63 ... resonance chamber 64 ... sound emission hole 65 ... recess 71 ... electrode 72 ... insulating layers 73 and 74 ... Input terminal 75: fixing member 76: adhesive layer 77: insulating layer 200, 300: wavefront

Claims (14)

Oscillating means for generating a signal whose voltage oscillates at a frequency in the ultrasonic band,
An amplitude modulator that amplitude-modulates a signal generated by the oscillation unit based on an audio signal;
A parametric speaker comprising: at least one electroacoustic transducer that converts a modulated signal modulated by the amplitude modulator into an ultrasonic wave and radiates the air into the air,
The oscillating means has an oscillating frequency variable,
A parametric loudspeaker characterized in that by changing the oscillation frequency of the oscillating means, it is possible to change the distance to a position where an audible sound is generated by self-demodulation of ultrasonic waves radiated from the electroacoustic transducer. The higher the oscillating frequency, the shorter the distance from the electroacoustic transducer to the position where audible sound is generated, and the lower the oscillating frequency, the distance from the electroacoustic transducer to the position where audible sound is generated. The parametric loudspeaker according to claim 1, wherein the length is longer. 3. The parametric speaker according to claim 1, wherein the oscillating means includes a voltage controlled oscillator. An electro-acoustic transducer array in which a plurality of the electro-acoustic transducers are arranged, and a phase control unit having a plurality of phase shifters that change a phase of the modulated signal input to each of the electro-acoustic transducers,
4. The parametric speaker according to claim 1, wherein the phase control unit changes the phase of the modulated signal input to each of the electroacoustic transducers, thereby changing a directional direction of sound. The phase of the modulated signal input to each of the electro-acoustic transducers is sequentially delayed from one end of the electro-acoustic transducer array toward the other end, so that the direction of sound is converted to the electro-acoustic conversion. 5. The parametric speaker according to claim 4, wherein the direction can be inclined with respect to the normal direction of the arrangement surface of the vessel. An electro-acoustic transducer array in which a plurality of the electro-acoustic transducers are arranged, and a phase control unit having a plurality of phase shifters that change a phase of the modulated signal input to each of the electro-acoustic transducers,
4. The parametric speaker according to claim 1, wherein a degree of directivity of sound can be changed by changing a phase of the modulated signal input to each of the electroacoustic transducers by the phase control unit. The phase of the modulated signal input to each of the electro-acoustic transducers is sequentially delayed from the center to the end of the electro-acoustic transducer array, and the phase difference between adjacent electro-acoustic transducers is in the center. 7. The parametric loudspeaker according to claim 6, wherein a state in which the sound radiation angle is gradually increased from the end to the end can increase a sound radiation angle and make the sound directivity relatively weak. The parametric speaker according to claim 1, further comprising an amplifier that amplifies the modulated signal input to the electroacoustic transducer. The electro-acoustic transducer,
A piezoelectric actuator that has a long shape and that expands and contracts in its longitudinal direction when the modulated signal is input,
A base supporting a base end of the piezoelectric actuator,
A vibration plate that is installed on the distal end side of the piezoelectric actuator and has a vibration unit that vibrates with expansion and contraction vibration of the piezoelectric actuator, and generates an ultrasonic wave,
9. The parametric speaker according to claim 1, further comprising: a resonator that resonates the generated ultrasonic waves. The parametric speaker according to claim 9, wherein the piezoelectric actuator has a portion in which a piezoelectric material and a conductive material are alternately stacked in layers. The electro-acoustic transducer,
A piezoelectric actuator that has a plate shape and that bends and vibrates when the modulated signal is input;
The parametric speaker according to any one of claims 1 to 8, further comprising: a resonator configured to resonate an ultrasonic wave generated by the vibration of the piezoelectric actuator. The parametric loudspeaker according to claim 11, wherein the electroacoustic transducer further includes a diaphragm that is joined to the piezoelectric actuator so as to overlap with the piezoelectric actuator and generates ultrasonic waves by vibrating in accordance with flexural vibration of the piezoelectric actuator. The electro-acoustic transducer,
A diaphragm that vibrates due to the Coulomb force generated by the input of the modulated signal and generates ultrasonic waves,
9. The parametric speaker according to claim 1, further comprising: a resonator that resonates the generated ultrasonic waves. The parametric transducer according to claim 13, wherein the electroacoustic transducer further includes an electrode disposed to face the diaphragm with a gap therebetween, and wherein the Coulomb force acts between the diaphragm and the electrode. Speaker.

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