JP2004312394A - Parametric speaker and electroacoustic transducer therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroacoustic transducer for a parametric speaker which is excellent in conversion of an electric signal into an ultrasonic wave and is advantageous in miniaturization , and to provide a parametric speaker. <P>SOLUTION: The electroacoustic transducer 2 for a parametric speaker is used for a parametric speaker, converts the inputted electric signal into an ultrasonic wave, and radiates it. This electroacoustic transducer 2 is provided with a piezoelectric actuator 3 having a long shape and stretching vibrating in the longitudinal direction by inputting an electric signal, a base 4 for supporting the base end of the piezoelectric actuator 3, a diaphragm 5 provided on the end side of the piezoelectric actuator 3 having a vibrating section 51 vibrating so as to generate an ultrasonic wave in response to the stretching vibration of the piezoelectric actuator 3, and a resonator 6 for allowing the ultrasonic wave generated by the diaphragm 5 to resonate. <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。
【００４３】
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が得られる。
【００４４】
また、電気音響変換器２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７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７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７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７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２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。
【００４５】
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２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。
【００４６】
図４は、本発明のパラメトリックスピーカ用電気音響変換器による他の実施形態を示す斜視図である。図４に示す電気音響変換器２’では、前記電気音響変換器２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２’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４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２’は、前記電気音響変換器２と同様である。
【００４７】
図５は、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６は、パラメトリックスピーカの原理を説明するための図である。以下、同図に基づいて、本発明のパラメトリックスピーカの実施形態について説明する。
図５に示すパラメトリックスピーカ（パラメトリックアレイスピーカ）１は、前述した電気音響変換器２と、発振器（搬送波発生手段）１１と、振幅変調器（振幅変調手段）１２と、増幅器（増幅手段）１３と、音声入力インターフェース１４とを備えている。
このパラメトリックスピーカ１は、可聴音（音声信号）によって超音波帯域の周波数をもつ搬送波（信号）を振幅変調したものを空中に放射し、空気の非線型特性を利用して可聴音を復調（自己復調）することにより、指向性の高い音響放射を行うことができるスピーカである。
【００４８】
パラメトリックスピーカ１における電気音響変換器２の設置個数は、１個でもよいが、複数個であるのが好ましい。この設置個数の調整により、十分な大きさ（音圧）の可聴音を発生させることができる。前述したように、本発明の電気音響変換器２は、小型化に有利であるので、多数の電気音響変換器２を高い集積度（密度）で配置することができる。
【００４９】
発振器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。発振器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。
【００５０】
図示しない音声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、発振器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。
【００５１】
振幅変調器１２によって変調された被変調信号は、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。増幅器１３で増幅された被変調信号は、電気音響変換器２に入力される。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（図２中の上方向に）放射する。
【００５２】
電気音響変換器２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、空気中を伝搬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。
【００５３】
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６に基づいてさらに説明する。図６（ａ）は、伝送波、すなわち音声生成器から出力された音声信号の波形である。図６（ｂ）は、発振器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６（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６（ｄ）のように歪んでゆき、元の可聴音が復調されていく（図６（ｅ））。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。
【００５４】
このようなパラメトリックスピーカ１では、電気音響変換器２の圧電アクチュエータ３の伸縮振動の固有振動数ν_１と、発振器１１の発振周波数ν_２とが近傍にあるのが好ましい。ここで、ν_１とν_２とが近傍にあるとは、好ましくは０．８≦ν_１／ν_２≦１．２、より好ましくは０．９≦ν_１／ν_２≦１．１なる関係を満足することを言う。ただし、固有振動数ν_１は駆動中の発熱などによって微妙に変化するので、実際には、ほんのわずかに発振周波数ν_２をずらすことによって結果として安定する条件を選ぶことも好ましい。以上のような条件を満足することにより、圧電アクチュエータ３を共振現象によって比較的低い電圧でもより大きな振幅で振動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。
【００５５】
また、パラメトリックスピーカ１では、発振器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５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。
【００５６】
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、圧電アクチュエータ３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５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。
【００５７】
さらに、パラメトリックスピーカ１では、圧電アクチュエータ３の固有振動数ν_１と、発振器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。
なお、このようなパラメトリックスピーカ１は、複数の電気音響変換器２を有するものである場合、複数（複数組）の電気音響変換器２から互いに異なる周波数の超音波を放射してもよい。
【００５８】
以上、本発明のパラメトリックスピーカ用電気音響変換器および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用電気音響変換器および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。
【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用電気音響変換器の実施形態を示す斜視図。
【図２】本発明のパラメトリックスピーカ用電気音響変換器の実施形態を示す断面側面図。
【図３】本発明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４】本発明のパラメトリックスピーカ用電気音響変換器の他の実施形態を示す斜視図。
【図５】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６】パラメトリックスピーカの原理を説明するための図。
【符号の説明】
１……パラメトリックスピーカ １１……発振器 １２……振幅変調器 １３……増幅器 １４……音声入力インターフェース ２、２’……パラメトリックスピーカ用電気音響変換器 ３、３’……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 ４……基台 ４１……突部 ５、５’……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 ７……固定部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electroacoustic transducer for a parametric speaker and a parametric speaker.
[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 a sound wave in an ultrasonic band having high directivity, and thus has high directivity in the direction in which the sound is directed.
[0003]
However, in a conventional parametric speaker, the conversion efficiency of an electroacoustic transducer serving as an ultrasonic source was poor and large. For this reason, the conventional parametric speaker has many disadvantages, such as heavy weight, large size, large power consumption, poor sound quality, and high manufacturing cost. And the parametric loudspeaker has a low energy efficiency due to the loss that occurs when it is converted into an audible sound by self-demodulation, so it has been extremely difficult to overcome the above-mentioned drawbacks.
[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 an electroacoustic transducer for a parametric speaker and a parametric speaker that are excellent in conversion efficiency when converting an electric signal into an ultrasonic wave and that are advantageous for miniaturization.
[0006]
[Means for Solving the Problems]
Such an object is achieved by the present invention described below.
An electroacoustic transducer for a parametric speaker of the present invention is used for a parametric speaker, and is an electroacoustic transducer for a parametric speaker that converts an input electric signal into an ultrasonic wave and radiates it.
A piezoelectric actuator that has a long shape and that expands and contracts in its longitudinal direction when the electric signal is input,
A base supporting a base end of the piezoelectric actuator,
A vibration plate that is installed on the tip side of the piezoelectric actuator and has a vibration unit that vibrates so as to generate an ultrasonic wave with expansion and contraction vibration of the piezoelectric actuator,
A resonator that resonates the ultrasonic waves generated by the diaphragm.
Thus, it is possible to provide an electroacoustic transducer for a parametric speaker that is excellent in conversion efficiency when converting an electric signal into an ultrasonic wave and is advantageous in miniaturization. In a parametric speaker using this electroacoustic transducer for a parametric speaker, reduction in power consumption, reduction in size and weight, and reduction in cost can be achieved.
[0007]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the resonator has a resonance chamber and a sound emission hole communicating with the resonance chamber.
As a result, the sound pressure of the ultrasonic wave can be radiated more strongly, further excellent conversion efficiency can be obtained, and the directivity of sound, which is a characteristic of the parametric speaker, can be more fully utilized.
[0008]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the sound emission hole is formed at a position that is not opposed to a front end surface of the piezoelectric actuator.
Thus, when a plurality of parametric speaker electro-acoustic transducers are arranged side by side, the arrangement of the sound emission holes of each parametric speaker electro-acoustic transducer can be determined with a high degree of freedom.
[0009]
In the electroacoustic transducer for a 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.
As a result, the piezoelectric actuator can obtain a large amount of displacement even at a relatively low voltage and has excellent controllability (responsivity), so that a further excellent conversion efficiency can be obtained. Excellent sound quality 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.
[0010]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the piezoelectric material and the conductive material are stacked in parallel with a direction in which the piezoelectric actuator expands and contracts.
Thereby, the piezoelectric actuator can obtain higher energy efficiency as compared with other vibration modes.
[0011]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the piezoelectric material and the conductive material are stacked perpendicularly to a direction in which the piezoelectric actuator expands and contracts.
Thus, the piezoelectric actuator can be stacked in a multilayer structure, and can be driven at a lower voltage.
[0012]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the base and the resonator are fixed via a fixing member.
Thus, during manufacture (assembly), the relative position between the fixing member and the base can be adjusted to accurately position the piezoelectric actuator with respect to the resonator (diaphragm), thereby facilitating manufacture. be able to.
[0013]
In the electroacoustic transducer for a parametric speaker of the present invention, the electroacoustic transducer for a parametric speaker includes a sound emitting plate that is overlapped and joined to the diaphragm, and a concave portion formed on at least one joint surface side of the diaphragm and the sound emitting plate. Preferably, a resonance chamber of the resonator is formed.
This makes it possible to easily manufacture (assembly) the resonator portion.
[0014]
In the electroacoustic transducer for a parametric speaker according to the present invention, the diaphragm, the spacer plate, and the sound emission plate are overlapped and joined in this order, and are formed between the diaphragm and the sound emission plate by the spacer plate. Preferably, at least a part of the resonance chamber of the resonator is formed by the space defined.
This makes it possible to easily manufacture (assembly) the resonator portion.
[0015]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that the piezoelectric actuator is fixed so that a surface parallel to a direction in which the piezoelectric actuator expands and contracts overlaps the base.
Thus, the piezoelectric actuator can be easily and firmly fixed to the base.
[0016]
In the electroacoustic transducer for a parametric speaker according to the present invention, it is preferable that a length of the base in a direction of expansion and contraction of the piezoelectric actuator is longer than a length of the piezoelectric actuator.
Thereby, manufacture (assembly) of the electroacoustic transducer for a parametric speaker can be easily performed.
[0017]
The parametric speaker of the present invention comprises: an electroacoustic transducer for at least one parametric speaker of the present invention;
An oscillator that generates a signal whose voltage oscillates at a frequency in the ultrasonic band,
An amplitude modulator that amplitude-modulates the signal based on an audio signal;
An amplifier that amplifies the modulated signal modulated by the amplitude modulator,
The modulated signal amplified by the amplifier is input to the parametric loudspeaker electro-acoustic transducer to emit ultrasonic waves.
This makes it possible to provide a parametric speaker capable of reducing power consumption, miniaturization, weight reduction, and cost reduction.
[0018]
In the parametric speaker according to the present invention, it is preferable that a natural frequency of expansion and contraction vibration of the piezoelectric actuator of the electroacoustic transducer for the parametric speaker and an oscillation frequency of the oscillator are close to each other.
As a result, the piezoelectric actuator can be vibrated with a larger amplitude due to the resonance phenomenon, so that the conversion efficiency of the electroacoustic transducer can be further improved, and the power consumption can be further reduced, and the size and weight can be further reduced.
[0019]
In the parametric loudspeaker of the present invention, it is preferable that the resonance frequency of the resonator of the electroacoustic transducer for a parametric loudspeaker and the oscillation frequency of the oscillator are close to each other or close to a harmonic relationship.
This allows the ultrasonic waves generated by the diaphragm to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer can be further improved, and further reduction in power consumption and reduction in size and weight can be achieved.
[0020]
In the parametric speaker according to the present invention, it is preferable that the natural frequency of the expansion and contraction vibration of the piezoelectric actuator of the electroacoustic transducer for a parametric speaker and the resonance frequency of the resonator are in the vicinity or in the vicinity of the overtone relationship.
This allows the ultrasonic waves generated by the diaphragm to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer can be further improved, and further reduction in power consumption and reduction in size and weight can be achieved.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an electroacoustic transducer for a parametric speaker and a parametric speaker of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
1 and 2 are a perspective view and a sectional side view, respectively, showing an embodiment of an electroacoustic transducer for a parametric speaker of the present invention. In addition, below, for convenience of explanation, the upper side in FIGS. 1 and 2 is referred to as a “distal end”, and the lower side is referred to as a “proximal end”.
[0022]
The electroacoustic transducer 2 for a parametric speaker (hereinafter simply referred to as “electroacoustic transducer 2”) shown in FIGS. 1 and 2 is used for a parametric speaker, and converts an input electric signal into an ultrasonic wave (ultrasonic wave). (Sonic vibration) and radiate into the air. Note that the overall configuration of the parametric speaker 1 including the electroacoustic transducer 2 will be described later.
The electroacoustic transducer 2 includes a piezoelectric actuator (piezoelectric vibrating body) 3 having a long shape (an elongated shape), a base 4 supporting a base end (fixed end) of the piezoelectric actuator 3, and a piezoelectric actuator 3. A vibration plate 5 installed on the tip (free end) side of the device, a resonator 6 for resonating the ultrasonic waves generated by the vibration plate 5, and a fixing member 7.
[0023]
As shown in FIG. 1, in the present embodiment, a configuration (electro-acoustic transducer array) in which a plurality of electro-acoustic transducers 2 arranged in n rows × 2 columns (n is an integer of 2 or more) is integrated. ing. In this electroacoustic transducer array, the base 4, the diaphragm 5, the resonator 6, and the fixing member 7 (the fixing member 7 is omitted in FIG. 1) are integrated with each of the electroacoustic transducers 2. Is formed.
As shown in FIG. 2, the electro-acoustic transducers 2 in the left-hand column and the electro-acoustic transducers 2 in the right-hand row in FIG. The plurality of electroacoustic transducers 2 in each row have the same structure. Therefore, hereinafter, one electroacoustic transducer 2 will be described as a representative.
[0024]
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.
[0025]
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 row direction (a direction perpendicular to the paper surface of FIG. 2) 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.
[0026]
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.
[0027]
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 2, a conductive material (conductive member) (not shown) 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.
In the piezoelectric actuator 3 shown in FIG. 2, since the piezoelectric material and the conductive material (electrode) are arranged in parallel to the expansion and contraction direction (longitudinal direction), higher energy efficiency can be obtained as compared with other vibration modes. .
[0028]
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. Further, as described later, the natural frequency ν ₁ Is the oscillation frequency ν of the oscillator 11 of the parametric speaker 1. ₂ Is more preferable. Also, 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.
[0029]
FIG. 3 is a perspective view showing another configuration example of the piezoelectric actuator according to the present invention. In the piezoelectric actuator 3 ′ shown in FIG. 3, a piezoelectric material and a conductive material are stacked perpendicularly to the expansion and contraction direction (longitudinal direction) of the piezoelectric actuator 3 ′. In the present invention, a piezoelectric actuator 3 'may be used in place of the piezoelectric actuator 3. In the piezoelectric actuator 3 ′ shown in FIG. 3, since the piezoelectric material and the conductive material can be stacked in more layers, they can be driven at a lower voltage.
[0030]
As shown in FIG. 2, the base 4 has, at a base end portion thereof, a protrusion 41 protruding laterally for fixing the piezoelectric actuator 3. 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 the present invention, since the base end of the piezoelectric actuator 3 is fixed to the base 4, the piezoelectric actuator 3 does not need to have much strength due to the strength (rigidity) of the base 4. This is 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.
[0031]
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 4 has its base end (base end face) fixed to the fixing member 7. The tip (tip face) of the base 4 is joined (fixed) to the diaphragm 5. The fixing member 7 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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
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. 1). .
[0036]
When an electric signal (oscillation voltage) whose voltage oscillates at a frequency in the ultrasonic band is input to the piezoelectric actuator 3 of the electroacoustic transducer 2, the piezoelectric actuator 3 expands and contracts in its longitudinal direction. The vibration part 51 of the vibration plate 5 vibrates to generate ultrasonic waves. The ultrasonic waves generated by the diaphragm 5 resonate in the resonator 6 and are emitted upward in FIG.
[0037]
The constituent materials of the base 4, the sound emitting plate 61, the spacer plate 62, and the fixing member 7 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.
[0038]
In the electro-acoustic transducer 2 of the present invention, 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) ( Hereinafter, it may be 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.
[0039]
Furthermore, the electro-acoustic transducer 2 of the present invention is extremely advantageous for miniaturization, and when many electro-acoustic transducers 2 are arranged in a matrix, for example, the number of arrangements per unit area can be extremely increased. . Therefore, even with a relatively small parametric speaker, an audible sound of sufficient intensity can be obtained, and the size and weight of the parametric speaker can be reduced.
[0040]
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 in power consumption, reduction in size and weight) are more remarkably exhibited, and the directivity of sound, which is a characteristic of the parametric speaker, can be more fully utilized.
[0041]
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 stretching vibration of the piezoelectric actuator 3 ₁ And the oscillation frequency ν of the oscillator 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.
[0042]
(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). .
[0043]
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. In this case, a parametric speaker with lower power (low power consumption) and higher efficiency can be obtained.
[0044]
Further, in the electroacoustic transducer 2, 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 7 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. Further, since the base plate 4 is fixed to the fixing member 7 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 7 can be configured as separate members. That is, a material having high rigidity enough to receive a 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 7. . For this reason, in the electroacoustic transducer 2, it is possible to achieve both high performance (high conversion efficiency) and low manufacturing cost at a high level.
[0045]
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 2 of the present embodiment can obtain more excellent conversion efficiency, and can obtain better sound quality when used in 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.
[0046]
FIG. 4 is a perspective view showing another embodiment of the electro-acoustic transducer for a parametric speaker of the present invention. In the electro-acoustic transducer 2 ′ shown in FIG. 4, unlike the electro-acoustic transducer 2, 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 ′. Have been. 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 2 ′. However, in order to make the recesses 54 and 55 independent as a resonator, the recesses 54 and 55 are preferably separated by forming a partition wall. desirable. In the embodiment shown in FIG. 4, the spacer plate 62 becomes unnecessary, and the assembly process can be simplified. Except for the above, the electroacoustic transducer 2 ′ is the same as the electroacoustic transducer 2.
[0047]
FIG. 5 is a block diagram showing an embodiment of the parametric speaker of the present invention, and FIG. 6 is a diagram for explaining the principle of the parametric speaker. Hereinafter, an embodiment of the parametric speaker of the present invention will be described with reference to FIG.
The parametric speaker (parametric array speaker) 1 shown in FIG. 5 includes an electroacoustic transducer 2, an oscillator (carrier generation means) 11, an amplitude modulator (amplitude modulation means) 12, an amplifier (amplification means) 13, , A voice input interface 14.
The parametric speaker 1 radiates, in the air, a carrier (signal) having a frequency in an ultrasonic band, which is amplitude-modulated by an audible sound (sound signal), and demodulates the audible sound using the non-linear characteristic of air (self This is a speaker that can perform highly directional acoustic radiation by demodulation.
[0048]
The number of the electroacoustic transducers 2 provided in the parametric speaker 1 may be one, but it is preferable that the number is plural. By adjusting the number of installations, an audible sound having a sufficient volume (sound pressure) can be generated. As described above, since the electroacoustic transducer 2 of the present invention is advantageous for miniaturization, a large number of electroacoustic transducers 2 can be arranged with a high degree of integration (density).
[0049]
The oscillator 11 generates (generates) a signal (carrier) whose voltage oscillates at a frequency (about 20 kHz or more) in the ultrasonic band. Oscillation frequency of oscillator 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.
[0050]
The audio signal generated by the audio 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 oscillator 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.
[0051]
The modulated signal modulated by the amplitude modulator 12 is input to the amplifier 13 and is amplified to a level at which the electroacoustic transducer 2 can be driven. The modulated signal amplified by the amplifier 13 is input to the electroacoustic transducer 2. The electroacoustic transducer 2 converts the input signal into an ultrasonic wave, and radiates it into the air with directivity (upward in FIG. 2).
[0052]
The ultrasonic wave (modulated wave) emitted from the electroacoustic transducer 2 into the air becomes a distorted wave due to the non-linear characteristics of the air, and is demodulated to an audible sound of the original audio signal while propagating in 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).
[0053]
The principle of the above parametric speaker 1 will be further described with reference to FIG. FIG. 6A shows the waveform of the transmission wave, that is, the audio signal output from the audio generator. FIG. 6B shows a waveform of a signal (carrier) generated by the oscillator 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. 6 (d) because the air travels faster when vibrating 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. 6 (e)). The demodulated audible sound has the super directional characteristics of the original ultrasonic wave.
[0054]
In such a parametric speaker 1, the natural frequency ν of the expansion and contraction vibration of the piezoelectric actuator 3 of the electroacoustic transducer 2. ₁ And the oscillation frequency ν of the oscillator 11 ₂ Are preferably in the vicinity. Where ν ₁ And ν ₂ Is in the vicinity, preferably 0.8 ≦ ν ₁ / Ν ₂ ≦ 1.2, more preferably 0.9 ≦ ν ₁ / Ν ₂ It satisfies the relationship of ≦ 1.1. Where the natural frequency ν ₁ Actually changes slightly due to heat generation during driving. ₂ It is also preferable to select conditions that stabilize as a result by shifting. By satisfying the above conditions, the piezoelectric actuator 3 can be oscillated with a larger amplitude by a resonance phenomenon even at a relatively low voltage, so that the conversion efficiency of the electroacoustic transducer 2 can be further improved.
[0055]
In the parametric speaker 1, the oscillation frequency ν of the oscillator 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 5 to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer 2 can be further improved.
[0056]
In the parametric speaker 1, the resonance frequency ν of the resonator 6 ₃ And the natural frequency ν of the piezoelectric actuator 3 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 Is in the vicinity in the same manner as described above. This allows the ultrasonic waves generated by the diaphragm 5 to resonate more strongly, so that the conversion efficiency of the electroacoustic transducer 2 can be further improved.
[0057]
Furthermore, in the parametric speaker 1, the natural frequency ν of the piezoelectric actuator 3 ₁ And the oscillation frequency ν of the oscillator 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.
When such a parametric speaker 1 has a plurality of electroacoustic transducers 2, a plurality (a plurality of sets) of electroacoustic transducers 2 may emit ultrasonic waves having mutually different frequencies.
[0058]
As described above, the embodiment of the electroacoustic transducer for a parametric speaker and the parametric speaker according to the present invention has been described with reference to the drawings. However, the present invention is not limited to this. Each of the components can be replaced with an arbitrary component having the same function. Further, an arbitrary component may be added.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of an electroacoustic transducer for a parametric speaker of the present invention.
FIG. 2 is a sectional side view showing an embodiment of an electroacoustic transducer for a parametric speaker of the present invention.
FIG. 3 is a perspective view showing another configuration example of the piezoelectric actuator according to the present invention.
FIG. 4 is a perspective view showing another embodiment of the electroacoustic transducer for a parametric speaker of the present invention.
FIG. 5 is a block diagram showing an embodiment of the parametric speaker of the present invention.
FIG. 6 is a diagram illustrating the principle of a parametric speaker.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Parametric speaker 11 ... Oscillator 12 ... Amplitude modulator 13 ... Amplifier 14 ... Voice input interface 2, 2 '... Electroacoustic converter for parametric speakers 3, 3' ... Piezoelectric actuator 31 ... 1 piezoelectric material layer 32 first conductive layer 33 second piezoelectric material layer 34 second conductive layer 35, 36 collector electrode 4 base 41 protrusions 5, 5 '... Vibrating plate 51 ... Vibrating part 52, 53, 54, 55 ... Recess 6 ... Resonator 61, 61' ... Sound emitting plate 62 ... Spacer plate 621 ... Recess 622 ... Through hole 63 ... … Resonant chamber 64… Sound emission hole 65… Recess 7… Fixation member

Claims (15)

An electroacoustic transducer for a parametric speaker, which is used for a parametric speaker and converts an input electric signal into an ultrasonic wave and emits the ultrasonic wave,
A piezoelectric actuator that has a long shape and that expands and contracts in its longitudinal direction when the electric signal is input,
A base supporting a base end of the piezoelectric actuator,
A vibration plate that is installed on the tip side of the piezoelectric actuator and has a vibration unit that vibrates so as to generate an ultrasonic wave with expansion and contraction vibration of the piezoelectric actuator,
A resonator for resonating the ultrasonic waves generated by the diaphragm. The electro-acoustic transducer for a parametric speaker according to claim 1, wherein the resonator has a resonance chamber and a sound emission hole communicating with the resonance chamber. The electro-acoustic transducer for a parametric speaker according to claim 2, wherein the sound emission hole is formed at a position that is not opposed to a front end surface of the piezoelectric actuator. 4. The electro-acoustic transducer for a parametric speaker according to claim 1, 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 for a parametric speaker according to claim 4, wherein the piezoelectric material and the conductive material are stacked in parallel with a direction in which the piezoelectric actuator expands and contracts. The electro-acoustic transducer for a parametric speaker according to claim 4, wherein the piezoelectric material and the conductive material are stacked perpendicularly to a direction in which the piezoelectric actuator expands and contracts. The electroacoustic transducer for a parametric speaker according to any one of claims 1 to 6, wherein the base and the resonator are fixed via a fixing member. A sound emitting plate, which is joined to the vibrating plate so as to overlap with the vibrating plate, wherein a resonance chamber of the resonator is formed by a concave portion formed on at least one joint surface of the vibrating plate and the sound emitting plate. 8. The electroacoustic transducer for a parametric speaker according to any one of 1 to 7. The diaphragm, the spacer plate, and the sound emitting plate are overlapped and joined in this order, and at least the resonance chamber of the resonator is formed by a space formed between the diaphragm and the sound emitting plate by the spacer plate. The electroacoustic transducer for a parametric speaker according to any one of claims 1 to 7, wherein the electroacoustic transducer is partially formed. The electroacoustic transducer for a parametric speaker according to any one of claims 1 to 9, wherein the piezoelectric actuator is fixed so that a surface parallel to a direction of expansion and contraction overlaps the base. The electroacoustic transducer for a parametric speaker according to any one of claims 1 to 10, wherein a length of the base in a direction of expansion and contraction of the piezoelectric actuator is longer than a length of the piezoelectric actuator. An electroacoustic transducer for at least one parametric speaker according to any of claims 1 to 11,
An oscillator that generates a signal whose voltage oscillates at a frequency in the ultrasonic band,
An amplitude modulator that amplitude-modulates the signal based on an audio signal;
An amplifier that amplifies the modulated signal modulated by the amplitude modulator,
A parametric speaker characterized in that the modulated signal amplified by the amplifier is input to the parametric speaker electroacoustic transducer to emit ultrasonic waves. 13. The parametric speaker according to claim 12, wherein a natural frequency of expansion and contraction vibration of a piezoelectric actuator of the parametric speaker electroacoustic transducer and an oscillation frequency of the oscillator are close to each other. 14. The parametric speaker according to claim 12, wherein a resonance frequency of a resonator of the electroacoustic transducer for a parametric speaker and an oscillation frequency of the oscillator are close to each other or close to a harmonic relationship. The parametric speaker according to any one of claims 12 to 14, wherein a natural frequency of expansion and contraction vibration of a piezoelectric actuator of the electroacoustic transducer for a parametric speaker and a resonance frequency of the resonator are close to each other or close to a harmonic relationship. .

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