JP3714904B2

JP3714904B2 - Electroacoustic transducer

Info

Publication number: JP3714904B2
Application number: JP2001386312A
Authority: JP
Inventors: 学岡本; 正人三好; 好章渡辺; 裕司細井; 義春岩下
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2001-12-19
Filing date: 2001-12-19
Publication date: 2005-11-09
Anticipated expiration: 2021-12-19
Also published as: JP2003189381A

Description

【０００１】
【発明の属する技術分野】
この発明は人体の一部に振動を与え、その振動を音として知覚させることに利用することができる電気音響変換装置に関する。
【０００２】
【従来の技術】
人間に音を知覚させる方法の一つに骨導伝達方法が実用化されている。骨導伝達方法とは人体の主に頭部に音響振動を与え、この音響振動を人体の骨、肉等を通じて聴覚系に伝達し、音として知覚させる方法である。この骨導伝達方法によれば耳の不自由な方にも音を知覚させることができる。
骨導伝達方法を実現する場合、加振手段により可聴周波数で音響振動を発生させ、この音響振動を人の頭部に与える方法が考えられる。この方法を採る場合、音響振動が周囲に漏れ周囲の人に騒音として聴こえる欠点がある。
【０００３】
このため、非可聴振動である超音波信号を可聴信号で振幅変調し、この振幅変調された超音波信号により超音波振動子を駆動し、振幅変調された超音波振動で人体の頭部を加振することにより、人体の内部で超音波の復調作用により可聴振動を復調し、この可聴振動を聴覚系に伝達する方法も考えられている。この超音波方式の骨導伝達方法によれば周囲に音が漏れない利点が得られる。
図２１にその超音波方式の骨導ヘッドホンの概略の構成を示す。非可聴帯域（超音波帯域）で加振可能な加振手段１を皮膚に接触させ、人の体を加振できるように装着する。超音波信号発生手段２から出力された２０ｋＨｚ〜５０ｋＨｚ程度の非可聴の超音波信号を振幅変調手段４により、可聴信号である入力信号３により振幅変調し加振手段１に入力する。加振手段１から人体内に伝えられた非可聴振動は非線形効果により可聴振動を生成し、音として知覚することが可能となる。生成された可聴振動は変調に用いた入力信号３に対応した振動となる。従って、入力信号３に音楽や音声などの信号を用いることにより、音楽や音声を受聴することが可能な骨導ヘッドホン装置を作ることが可能である。
【０００４】
【発明が解決しようとする課題】
しかし、従来の骨導ヘッドホンは加振手段１の非可聴振動を人体内で非線形効果により可聴振動に変換するため、人体内に高エネルギーの振動を伝達する必要があり、人体に負担がかかるという第一の課題があった。
また、従来の骨導ヘッドホンでは加振手段１自身が持つ音響インピーダンスと人体の音響インピーダンスは材質の違いにより大きく異なり、加振手段１と人体の接触面で振動エネルギーが反射し、振動を効率良く人体に伝達できないと言う第二の課題があった。
【０００５】
また、従来の骨導ヘッドホンでは加振手段１の素材となる圧電素子は、一般的に周波数特性が平坦でなく加振手段の共振周波数で極度のピークを持つ。また入力電圧と音圧の関係が非線形になる。そのため、音質の制御等が困難であるという第三の課題があった。
【０００６】
【課題を解決するための手段】
この発明では、少なくとも可聴領域よりも高い周波数の超音波信号を発生する超音波信号発生手段と、超音波信号を可聴領域の音声信号で振幅変調して被変調信号を得る変調手段と、被変調信号の振幅に反映した非可聴振動を発生する加振手段と、加振手段に接触し人体の音響インピーダンスに略々等しく接触加速度と音響出力の振幅との間に非線形特性を有する振動素材と、加振手段の振動面を表面にして加振手段を格納する筐体とを備えた電気音響変換装置を提案する。
この発明では少なくとも可聴領域よりも高い周波数の超音波信号を発生する超音波信号発生手段と、超音波信号を可聴領域の音声信号で振幅変調して被変調信号を得る変調手段と、被変調信号によって非可聴振動を発生する加振手段と、加振手段に接触し、この接触面における音響インピーダンスが加振手段の音響インピーダンスにほぼ等しく、表面側における音響インピーダンスが人体の音響インピーダンスにほぼ等しくなるように加振手段の接触面から表面側にかけて各々の値に連続的に音響インピーダンスが変化する振動素材と、加振手段の振動面を表面にして加振手段を格納する筐体と、を備えた電気音響変換装置を提案する。
【０００７】
この発明では更に、少なくとも可聴領域よりも高い周波数の超音波信号を発生する超音波信号発生手段と、超音波信号を可聴領域の音声信号で振幅変調して被変調信号を得る変調手段と、被変調信号の振幅に反映した非可聴振動を発生する加振手段と、変調手段から加振手段へ供給される被変調信号の供給経路又は変調手段に供給される音声信号の供給経路の何れか一方に、加振手段の共振周波数より低い周波数領域では、加振手段の非可聴音の出力周波数特性が共振周波数との差の値を二乗した値に比例した特性に、また、加振手段の共振周波数より高い周波数領域では加振手段の非可聴音の出力周波数特性が共振周波数との差の値を二乗した値に反比例した特性に補正する周波数補正信号を得る補正手段を設けたことを特徴とする電気音響変換装置を提案する。
【０００８】
この発明では更に、請求項１又は２記載の電気音響変換装置の何れかにおいて、変調手段から加振手段へ供給される被変調信号の供給経路又は変調手段に供給される音声信号の供給経路の何れか一方に、加振手段の共振周波数より低い周波数領域では、加振手段の非可聴音の出力周波数特性が共振周波数との差の値を二乗した値に比例した特性に、また、加振手段の共振周波数より高い周波数領域では加振手段の非可聴音の出力周波数特性が共振周波数との差の値を二乗した値に反比例した特性に補正する周波数補正信号を得る補正手段を設けたことを特徴とする電気音響変換装置を提案する。
【０００９】
この発明では更に、請求項１乃至４記載の電気音響変換装置の何れかにおいて、音声信号と周波数補正信号とを加算した加算信号で加振手段を駆動する電気音響変換装置を提案する。
作用
この発明によれば、非線形効率の高い振動素材を加振手段と人体の間に挟む。これにより、人体内ではなく、振動素材の内部で可聴振動を生成し、人体にかかる負担を軽減することが可能となり、第一の課題を解決することができる。また、人体と音響インピーダンスが近い振動素材を用いることにより、振動素材の内部で生成した可聴信号を効率良く人体に伝達することが可能となり、第二の課題も解決することができる。
【００１０】
この発明によれば、振動素材の音響インピーダンスを加振手段に接する側から人体に接する側に連続的に変化させることにより、第二の課題を更に効率良く解決可能となる。音響インピーダンスを徐々に変化させることにより、振動素材の内部で生成された可聴信号は、素材の境界での振動は反射せず、効率よく人体に振動を伝えることが可能となる。
この発明によれば更に加振手段に入力する信号を補正手段により周波数特性を補正することにより、音質の制御が可能となり第三の課題が解決される。
この発明によれば、加振手段に超音波に加え、更に可聴信号を直接加算して入力することにより、非線形効果から生成される可聴振動の周波数特性を可聴信号により補正することを可能とし、第三の課題が解決される。
【００１１】
【発明の実施の形態】
図１にこの発明の実施例を示す。この発明では、図２１に示した従来の装置に対し、加振手段１の人体に接触する面に振動素材５を貼り付ける形で拡張したものとなる。ここで、振動素材５としては例えば高分子ゲル材で構成することができる。振動素材５を配置したことにより加振手段１の振動が人体に伝わる際に、振動素材５を経由して伝わることになる。加振手段１は人体を直接加振するのではなく、振動素材５を非可聴帯域の振動で加振する。加振手段１を振動させる信号に非可聴帯域の超音波信号を可聴信号で振幅変調した信号を用い駆動した場合、振動素材５の非線形性により、非可聴振動が人体に伝わる前に振動素材５の内部で可聴振動が発生する。
【００１２】
振動素材５に、非線形効率の高いもの（非線形効率の高い素材を選択する）を用いることにより、効率よく可聴振動を発生させることができ、また、人体の軟骨又は皮膚と音響インピーダンスが近いものを用いることにより、振動素材５で発生した可聴振動を人体との境界で減衰させることなく、効率よく人体内に可聴振動を伝えることが可能となる。また、高エネルギーの非可聴振動は振動素材５の内部で減衰するため、非可聴振動は人体に伝わりにくくなり、人体への負担も軽減する。
この発明では更に、図１の構成において、振動素材５を加振手段１に近い側から皮膚に接する側に向け、音響インピーダンスが徐々に変化する素材とするものである。
【００１３】
図２及び図３に振動素材５の音響インピーダンス変化の様子を示す。人体と振動素材５との接触面を垂直に交差する方向を「ｘ軸」として音響インピーダンスの変化の様子を図３に示す。加振手段１に近い側では、加振手段１に近い音響インピーダンスにすることにより振動を効率よく振動素材５に伝えると共に、この境界での外部への音漏れを防止する。人体に近い側では人体の軟骨、又は皮膚に近い音響インピーダンスにすることにより、振動素材５の内部で発生した可聴振動を人体へ効率よく、かつ、この境界での音漏れがしない形で振動を伝えることができる。加振手段１側から人体側へは連続的、もしくは段階的に徐々に音響インピーダンスを変化させることにより、素材の境界面で振動が反射や減衰することを防止することができる。
【００１４】
図４に他の実施例を示す。この実施例では上述した第三の課題として提示した音質の制御を可能とした電気音響変換装置を提案するものである。このため、この実施例では振動素材５は構成要素から外されている。一般に超音波振動を発生させることが可能なような加振手段１は、音響周波数特性が平坦ではない。また、入力電圧と出力となる加振パワーの関係も、線形ではない場合が多い。従って、超音波で振動を人体に伝える場合も、歪みが発生しやすく、また音質の制御が困難である。そのため、加振手段１に入力される信号等を補正手段６で補正することにより、非線形効果により発生する可聴音の周波数特性を平坦にする。
【００１５】
以下に補正手段６で補正する場合の方法の例を示す。超音波の非線形効果により振動素材５の内部に発生する可聴音の周波数特性は、変調の深さが一定の場合、理論的には周波数ωのほぼ二乗に比例し、従って図５に示すような特性となる。図５では生成する可聴音の最低周波数をωＬ（例えば２０Ｈｚ）、最高周波数をωＨ（例えば２０ＫＨｚ）としている。
加振手段１の周波数特性が超音波の周波数（キャリアの周波数）を中心に±２０ＫＨｚにわたって平坦な特性を持つものと仮定すると、非可聴振動から再現される可聴振動は図５に示した周波数の２乗（ω²）に比例した周波数特性を有する。この周波数特性を補正して平坦な周波数特性を得るためには、補正手段６に１／ω²の特性を持たせる必要がある。
【００１６】
ところで、システム全体の構成は図４に示す如くであり、加振手段１の周波数特性は図６に各種示すように必要帯域内で平坦でなく、共振周波数ω₀を中心に左右対称的に減衰している特性を持つ、つまり、図６に示す曲線Ａ１、Ａ２、Ａ３は超音波振動子の品種別の超音波出力の周波数特性を示す。
加振手段１が一般的な超音波振動子の周波数特性を持つ場合、周波数補正手段６としては上述した１／ω²の特性とは異なる特性が要求される。
いま、加振手段１の振幅周波数特性をＡ（ω）とすると、共振周波数を中心とする対称特性つまりＡ（ω₀＋ω）＝Ａ（ω₀−ω）。また、Ａ（ω₀）＝１となるようにＡ（ω）を規格化したとすると、この場合の周波数補正手段６の特性は１／（Ａ（ω₀＋ω）ω²）となる。従って、図７に示すように、加振手段１の振幅周波数特性Ｈ（ω）の等価低域特性Ｈ₁（ω）が１２ｄＢ／オクターブで減衰している場合には補正手段６が無くとも平坦な周波数特性と一定の高調波ひずみ率が得られる。
【００１７】
具体的に例示すると、共振周波数ωＣ（例えば４０ＫＨｚ）の超音波を可聴音（ωＬ＝２０Ｈｚ〜ωＨ＝２０ＫＨｚ）で変調する場合、その変調後の超音波信号を中心周波数ωＣと可聴信号（ωＬ〜ωＨまで）との差の周波数領域に（ωＣ−ωＨ）〜（ωＣ＋ωＨ）の側帯波として現れ、この範囲の加振手段１の周波数特性に影響を受けることになる。従って、図８に示すように、加振手段１の共振周波数ωＣより低い周波数領域（ωＣ−ωＨ）〜（ωＣ−ωＬ）の範囲では、周波数の差の二乗（ωＣ−ω）²に比例した特性に、加振手段１の共振周波数より高い周波数領域（ωＣ＋ωＬ）〜（ωＣ＋ωＨ）では周波数の差の二乗（ωＣ−ω）²に反比例する周波数特性を加振手段１が持つ場合、非線形効果で生成される可聴音の特性が平坦になり望ましいことになる。
【００１８】
しかし、現実には図９に示すように、圧電素子を使用した一般的な加振手段１の周波数特性は所望の特性と異なる。特に共振周波数ωＣの近傍では、周波数ピークが所望の特性より低い特性となる。従って、図９の特性が図８に示す理想的な特性になるように、補正手段６の周波数特性は図１０の様に設定される。尚、補正手段６としては例えばデジタルフィルタによって構成することができる。
また、図１１に一般的な加振手段１の入力対出力特性を示す。図１１に示す入力対出力特性Ａを持つ加振手段１を用いる場合、補正手段６の入力対出力特性Ｂを図１２に示すような特性（図１１の特性Ａとは逆の非直線特性Ｂ）にすることにより、装置の入力と加振手段１の出力特性を図１３に実線で示す様に直線化することができる。この結果、加振手段１から人体に伝わる振動の音圧の変化を直線化することが可能となる。
【００１９】
図４では変調後の信号に補正をかけ、周波数特性及び入出力特性を所望の特性に補正したが、図１４の様に、変調前の入力信号に対し、補正をかける構成も有効である。この場合には振幅変調により発生する側波帯ＳＵＬ：ＳＵＨ（図１５Ａ参照）の共振周波数（キャリアと同一周波数とする）ωＣに近い周波数成分ωＣ−ωＬ及びωＣ＋ωＬ側を強調した側波帯ＳＵＬ′とＳＵＨ′に補正することにより、加振手段１の超音波放射の周波数特性を図１５Ａに示す曲線Ｂ１からＢ２に補正することができる。この結果加振手段１の共振周波数ωＣより低い側では２乗曲線に比例した特性に補正することができ、また共振周波数ωＣより高い側では２乗曲線に反比例した特性に補正することができる。このためには補正器６の補正特性としては図１５Ｂに示すように低域強調特性とすればよい。
【００２０】
図１６は更に他の実施例を示す。この実施例では振動素材５を構成要素とする図１に示した実施例の特徴である補正手段６を加えたものである。補正手段６の周波数補正特性としては加振手段１に入力される信号に対し、あらかじめ加振手段１の周波数特性に加え、振動素材５の周波数特性にあわせて補正することにより、広い周波数特性で、平坦な特性の可聴振動を人体に与えることができる。図１６は変調後の信号に補正をかけるものだが、図４の場合と同様、変調前の入力信号に対し補正をかけることも有効である。
図１７では、この発明の更に他の実施例を示す。この実施例では加振手段１に入力される信号を、図１に示した振幅変調された非可聴信号に、可聴信号を加算した信号を得る加算手段７を備えたものとする。
【００２１】
非可聴振動の非線形効果による可聴信号の発生は、非線形な特性であるため、非常に音質の制御が難しい。図４及び図１６に示した実施例の様に、補正手段６により平坦にできる場合もあるが、加振手段１の特性によっては、補正手段６のみでは、補正が不可能な場合もある。その場合、可聴信号を混ぜることにより、非線形効果で発生する可聴信号を補う形で、人体に振動を伝えることが可能である。可聴帯域の信号は線形効果のみによる制御のため、非線形である非可聴帯域に比べ、制御が容易で、その結果、音質の制御がより容易になる。図１８は、同じくこの発明の更に他の実施例で、補正手段６を可聴振動と非可聴の変調振動それぞれ個別にかける場合の実施例を示す。加振手段１、振動素材５、および人体の特性は、可聴振動の帯域の場合と非可聴振動の帯域の場合で、周波数特性や入出力特性が異なるため、それぞれ個別に補正を行った方が、より細かい音質の制御が可能となる。図１８は変調後の非可聴信号に対して補正を行っているが、図４及び図１６と同様に変調前の入力信号に対して補正を行うことも有効である。
【００２２】
図１９及び図２０にこの発明による電気音響変換装置をヘッドホンに応用した実施例を示す。図１９及び図２０に示す１０はこの発明による電気音響変換装置を示す。この発明による電気音響変換装置１０は外観上は上述したように、加振手段１と、この加振手段１の振動面に装着した振動素材５とによって構成される。
１１はヘッドバンドを示す。ヘッドバンド１１の両端（図には一端側のみを示す）に蝶番１２に装着されているバネにより、その回動遊端側が常時被装着者の耳に近い部分に圧接される。レバー１３には更に支持棒１４が装着され、この支持棒１４の下端に電気音響変換装置１０が装着され、その振動面に装着されている振動素材５が被装着者の皮膚に圧接される。
【００２３】
【発明の効果】
以上説明したように、この発明によれば、非可聴振動の非線形効果により、可聴振動を発生させる加振手段により人体に効率よく可聴振動を音質補正した形で伝えることが可能となる。また、非線形効果を発生させる非可聴振動を極力人体に伝えず、安全に非線形効果を起こすことが可能となる。
【図面の簡単な説明】
【図１】この発明で提案した電気音響変換装置の一実施例を説明するためのブロック図。
【図２】この発明の要部の構成を説明するための図。
【図３】図２に示した要部の特性の一例を説明するための特性曲線図。
【図４】この発明で提案した電気音響変換装置の他の実施例を説明するためのブロック図。
【図５】超音波の非線形効果で発生する可聴音の周波数特性を説明するための特性曲線図。
【図６】一般的な超音波振動子の周波数特性を説明するための特性曲線図。
【図７】平坦な周波数特性を持つ可聴音を周波数補正無しに発声させるために必要な加振手段の等価低域特性と、加振手段の振幅周波数特性の一例を示す特性曲線図。
【図８】周波数補正することなく平坦な周波数特性を持つ可聴音を発生させることができる加振手段の周波数特性を示す特性曲線図。
【図９】加振手段の現実の周波数特性を説明するための特性曲線図。
【図１０】図９に示した加振手段の周波数特性を図８に示した理想的な周波数特性に補正するための補正手段の補正特性を説明するための特性曲線図。
【図１１】加振手段の入力対出力特性の一例を説明するための特性曲線図。
【図１２】図１１に示した入力対出力特性を直線化補正するための補正特性を説明するための特性曲線図。
【図１３】図１１に示した加振手段の入力対出力特性を図１２に示した補正特性で補正した結果を説明するための特性曲線図。
【図１４】この発明で提案した電気音響変換装置の変形実施例を説明するためのブロック図。
【図１５】図１４に示した実施例の補正特性を説明するための特性曲線図。
【図１６】この発明で提案した電気音響変換装置の更に他の実施例を説明するためのブロック図。
【図１７】この発明で提案した電気音響変換装置の更に他の実施例を説明するためのブロック図。
【図１８】この発明で提案した電気音響変換装置の更に他の実施例を説明するためのブロック図。
【図１９】この発明による電気音響変換装置をヘッドホンに応用した場合の正面図。
【図２０】図１９の側面図。
【図２１】従来の技術を説明するためのブロック図。
【符号の説明】
１加振手段５振動素材
２超音波信号発生手段６周波数補正手段
３入力信号７加算手段
４振幅変調手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroacoustic transducer that can be used for applying vibration to a part of a human body and perceiving the vibration as sound.
[0002]
[Prior art]
A bone conduction transmission method has been put to practical use as one of the methods for allowing humans to perceive sound. The bone conduction transmission method is a method in which acoustic vibration is applied mainly to the head of the human body, and this acoustic vibration is transmitted to the auditory system through the human bone, meat, etc., and perceived as sound. According to this bone conduction transmission method, sound can be perceived even by a hearing-impaired person.
When realizing the bone conduction transmission method, a method of generating an acoustic vibration at an audible frequency by an excitation means and applying the acoustic vibration to a human head is conceivable. When this method is adopted, there is a drawback that acoustic vibration leaks to the surroundings and can be heard as noise by the surrounding people.
[0003]
For this reason, an ultrasonic signal, which is inaudible vibration, is amplitude-modulated with an audible signal, an ultrasonic transducer is driven by the amplitude-modulated ultrasonic signal, and the human head is added with the amplitude-modulated ultrasonic vibration. A method of demodulating audible vibrations by demodulating ultrasonic waves inside the human body and transmitting the audible vibrations to the auditory system is also considered. This ultrasonic bone conduction transmission method provides the advantage that no sound leaks to the surroundings.
FIG. 21 shows a schematic configuration of the ultrasonic bone conduction headphone. The vibration means 1 that can be vibrated in a non-audible band (ultrasonic band) is brought into contact with the skin so that the human body can be vibrated. An inaudible ultrasonic signal of about 20 kHz to 50 kHz outputted from the ultrasonic signal generating means 2 is amplitude-modulated by the input signal 3 which is an audible signal by the amplitude modulating means 4 and inputted to the exciting means 1. The non-audible vibration transmitted from the vibration means 1 into the human body generates an audible vibration by a non-linear effect and can be perceived as a sound. The generated audible vibration is vibration corresponding to the input signal 3 used for modulation. Therefore, by using a signal such as music or voice as the input signal 3, it is possible to make a bone-conducting headphone device capable of listening to music or voice.
[0004]
[Problems to be solved by the invention]
However, since conventional bone-conducting headphones convert non-audible vibration of the vibration means 1 into audible vibration by a non-linear effect in the human body, it is necessary to transmit high-energy vibration to the human body, which places a burden on the human body. There was a first problem.
Further, in the conventional bone-conducting headphones, the acoustic impedance of the vibration means 1 itself and the acoustic impedance of the human body differ greatly depending on the material, and vibration energy is reflected at the contact surface between the vibration means 1 and the human body, so that vibration is efficiently performed. There was a second problem that it could not be transmitted to the human body.
[0005]
In the conventional bone-conducting headphones, the piezoelectric element that is the material of the vibration means 1 is generally not flat in frequency characteristics and has an extreme peak at the resonance frequency of the vibration means. In addition, the relationship between the input voltage and the sound pressure becomes nonlinear. For this reason, there is a third problem that it is difficult to control sound quality.
[0006]
[Means for Solving the Problems]
In this invention, an ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least an audible area, a modulating means for obtaining a modulated signal by amplitude-modulating the ultrasonic signal with an audio signal in the audible area, An excitation means that generates non-audible vibration reflected in the amplitude of the signal, and a vibration material that is in contact with the excitation means and has a non-linear characteristic between the contact acceleration and the amplitude of the acoustic output, approximately equal to the acoustic impedance of the human body, Proposed is an electroacoustic transducer provided with a housing for storing the vibration means with the vibration surface of the vibration means as a surface.
In this invention, an ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least the audible area, a modulating means for modulating the ultrasonic signal with an audio signal in the audible area to obtain a modulated signal, and a modulated signal The vibration means that generates non-audible vibrations by contact with the vibration means, the acoustic impedance at the contact surface is substantially equal to the acoustic impedance of the vibration means, and the acoustic impedance at the surface side is substantially equal to the acoustic impedance of the human body A vibration material whose acoustic impedance continuously changes in each value from the contact surface to the surface side of the vibration means, and a housing for storing the vibration means with the vibration surface of the vibration means as a surface. An electroacoustic transducer is proposed.
[0007]
The present invention further includes an ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least the audible area, a modulating means for obtaining a modulated signal by amplitude-modulating the ultrasonic signal with an audio signal in the audible area, Either an excitation unit that generates non-audible vibrations reflected in the amplitude of the modulation signal, a supply path of a modulated signal supplied from the modulation unit to the excitation unit, or a supply path of an audio signal supplied to the modulation unit In addition, in the frequency region lower than the resonance frequency of the vibration means, the output frequency characteristic of the non-audible sound of the vibration means is proportional to the value obtained by squaring the difference from the resonance frequency, and the resonance of the vibration means. In the frequency region higher than the frequency, there is provided correction means for obtaining a frequency correction signal for correcting the output frequency characteristic of the non-audible sound of the vibration means to a characteristic inversely proportional to a value obtained by squaring the difference from the resonance frequency. Electric sound To propose a conversion device.
[0008]
According to the present invention, in the electroacoustic transducer according to claim 1 or 2, the supply path of the modulated signal supplied from the modulation means to the excitation means or the supply path of the audio signal supplied to the modulation means. On the other hand, in the frequency region lower than the resonance frequency of the vibration means, the output frequency characteristic of the non-audible sound of the vibration means is proportional to the value obtained by squaring the value of the difference from the resonance frequency. In the frequency region higher than the resonance frequency of the means, there is provided a correction means for obtaining a frequency correction signal for correcting the output frequency characteristic of the non-audible sound of the vibration means to a characteristic inversely proportional to a value obtained by squaring the difference from the resonance frequency. An electroacoustic transducer characterized by the above is proposed.
[0009]
The present invention further proposes an electroacoustic transducer according to any one of claims 1 to 4, wherein the excitation means is driven by an addition signal obtained by adding the audio signal and the frequency correction signal.
Action According to the present invention, a vibration material having high nonlinear efficiency is sandwiched between the vibration means and the human body. As a result, audible vibration can be generated not in the human body but in the vibration material, and the burden on the human body can be reduced, thereby solving the first problem. Further, by using a vibration material having an acoustic impedance close to that of the human body, an audible signal generated inside the vibration material can be efficiently transmitted to the human body, and the second problem can be solved.
[0010]
According to the present invention, the second problem can be solved more efficiently by continuously changing the acoustic impedance of the vibration material from the side in contact with the vibration means to the side in contact with the human body. By gradually changing the acoustic impedance, the audible signal generated inside the vibrating material does not reflect the vibration at the boundary of the material, and can efficiently transmit the vibration to the human body.
According to the present invention, the frequency characteristic of the signal input to the excitation means is further corrected by the correction means, so that the sound quality can be controlled and the third problem is solved.
According to this invention, it is possible to correct the frequency characteristics of the audible vibration generated from the non-linear effect by the audible signal by directly adding and inputting the audible signal in addition to the ultrasonic wave to the vibration means, The third problem is solved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the present invention. In the present invention, the vibration material 5 is attached to the surface of the vibration means 1 that comes into contact with the human body with respect to the conventional apparatus shown in FIG. Here, the vibration material 5 can be composed of, for example, a polymer gel material. When the vibration material 5 is disposed, the vibration of the vibration means 1 is transmitted via the vibration material 5 when the vibration is transmitted to the human body. The vibration means 1 does not directly vibrate the human body, but vibrates the vibration material 5 with vibration in an inaudible band. When driven using a signal obtained by amplitude-modulating an inaudible ultrasonic signal with an audible signal as a signal for oscillating the excitation means 1, the vibration material 5 is transmitted before the inaudible vibration is transmitted to the human body due to the nonlinearity of the vibration material 5. An audible vibration is generated inside.
[0012]
By using a material having a high nonlinear efficiency (selecting a material having a high nonlinear efficiency) as the vibration material 5, an audible vibration can be efficiently generated, and a material having an acoustic impedance close to that of human cartilage or skin. By using it, the audible vibration generated in the vibration material 5 can be efficiently transmitted to the human body without being attenuated at the boundary with the human body. In addition, since the high-energy non-audible vibration is attenuated inside the vibration material 5, the non-audible vibration is not easily transmitted to the human body, and the burden on the human body is reduced.
Further, according to the present invention, in the configuration of FIG. 1, the vibration material 5 is a material whose acoustic impedance gradually changes from the side close to the vibration means 1 toward the side in contact with the skin.
[0013]
2 and 3 show how the acoustic impedance of the vibration material 5 changes. FIG. 3 shows how the acoustic impedance changes with the direction perpendicularly intersecting the contact surface between the human body and the vibration material 5 as the “x axis”. On the side close to the vibration means 1, the vibration is efficiently transmitted to the vibration material 5 by making the acoustic impedance close to that of the vibration means 1, and sound leakage to the outside at this boundary is prevented. By making the acoustic impedance close to the human cartilage or skin on the side close to the human body, the audible vibration generated inside the vibration material 5 can be efficiently transmitted to the human body and the sound is not leaked at this boundary. I can tell you. By changing the acoustic impedance continuously or stepwise from the vibration means 1 side to the human body side, it is possible to prevent vibration from being reflected or attenuated at the boundary surface of the material.
[0014]
FIG. 4 shows another embodiment. In this embodiment, an electroacoustic transducer capable of controlling the sound quality presented as the third problem described above is proposed. For this reason, in this embodiment, the vibration material 5 is removed from the constituent elements. Generally, the vibration means 1 capable of generating ultrasonic vibrations does not have a flat acoustic frequency characteristic. Also, the relationship between the input voltage and the excitation power to be output is often not linear. Accordingly, even when vibration is transmitted to the human body using ultrasonic waves, distortion is likely to occur, and control of sound quality is difficult. Therefore, the frequency characteristic of the audible sound generated by the non-linear effect is flattened by correcting the signal or the like input to the excitation unit 1 by the correction unit 6.
[0015]
An example of a method when correction is performed by the correction means 6 will be shown below. The frequency characteristic of the audible sound generated inside the vibration material 5 due to the nonlinear effect of the ultrasonic wave is theoretically proportional to the square of the frequency ω when the modulation depth is constant, and as shown in FIG. It becomes a characteristic. In FIG. 5, the lowest frequency of the audible sound to be generated is ωL (for example, 20 Hz), and the highest frequency is ωH (for example, 20 KHz).
Assuming that the frequency characteristic of the excitation means 1 has a flat characteristic over ± 20 KHz centering on the ultrasonic frequency (carrier frequency), the audible vibration reproduced from the non-audible vibration has the frequency shown in FIG. It has a frequency characteristic proportional to the square (ω ² ). In order to correct this frequency characteristic and obtain a flat frequency characteristic, the correction means 6 needs to have a 1 / ω ² characteristic.
[0016]
By the way, the configuration of the entire system is as shown in FIG. 4, and the frequency characteristics of the vibration means 1 are not flat within the necessary band as shown in FIG. 6 and attenuated symmetrically around the resonance frequency ω _0. That is, the curves A1, A2 and A3 shown in FIG. 6 indicate the frequency characteristics of the ultrasonic output for each type of ultrasonic transducer.
When the vibration means 1 has a frequency characteristic of a general ultrasonic transducer, the frequency correction means 6 is required to have a characteristic different from the 1 / ω ² characteristic described above.
Assuming that the amplitude frequency characteristic of the vibration means 1 is A (ω), the symmetrical characteristic centered on the resonance frequency, that is, A (ω ₀ + ω) = A (ω ₀ −ω). If A (ω) is normalized so that A (ω ₀ ) = 1, the characteristic of the frequency correction means 6 in this case is 1 / (A (ω ₀ + ω) ω ² ). Therefore, as shown in FIG. 7, when the equivalent low frequency characteristic H ₁ (ω) of the amplitude frequency characteristic H (ω) of the vibration means 1 is attenuated by 12 dB / octave, it is flat without the correction means 6. Frequency characteristics and constant harmonic distortion are obtained.
[0017]
Specifically, when an ultrasonic wave having a resonance frequency ωC (for example, 40 KHz) is modulated with an audible sound (ωL = 20 Hz to ωH = 20 KHz), the ultrasonic signal after the modulation is converted to a center frequency ωC and an audible signal (ωL˜). appear as sidebands of (ωC−ωH) to (ωC + ωH) in the frequency region of the difference from (up to ωH), and is affected by the frequency characteristics of the vibration means 1 in this range. Therefore, as shown in FIG. 8, in the frequency range (ωC−ωH) to (ωC−ωL) lower than the resonance frequency ωC of the vibration means 1, it is proportional to the square of the frequency difference (ωC−ω) ² . When the vibration means 1 has a frequency characteristic that is inversely proportional to the square of the frequency difference (ωC−ω) ² in the frequency range (ωC + ωL) to (ωC + ωH) higher than the resonance frequency of the vibration means 1, the nonlinear effect is caused. The characteristics of the audible sound produced will be flat and desirable.
[0018]
However, in reality, as shown in FIG. 9, the frequency characteristic of a general vibration means 1 using a piezoelectric element is different from a desired characteristic. Particularly in the vicinity of the resonance frequency ωC, the frequency peak has a lower characteristic than the desired characteristic. Accordingly, the frequency characteristic of the correction means 6 is set as shown in FIG. 10 so that the characteristic shown in FIG. 9 becomes the ideal characteristic shown in FIG. The correction means 6 can be constituted by a digital filter, for example.
FIG. 11 shows the input-to-output characteristics of the general vibration means 1. When the vibration means 1 having the input-to-output characteristic A shown in FIG. 11 is used, the input-to-output characteristic B of the correcting means 6 is changed to a characteristic as shown in FIG. 12 (a nonlinear characteristic B opposite to the characteristic A in FIG. 11). ), The input characteristics of the apparatus and the output characteristics of the vibration means 1 can be linearized as shown by the solid line in FIG. As a result, it is possible to linearize a change in sound pressure of vibration transmitted from the vibration means 1 to the human body.
[0019]
In FIG. 4, the modulated signal is corrected and the frequency characteristics and input / output characteristics are corrected to the desired characteristics. However, as shown in FIG. 14, a configuration for correcting the input signal before modulation is also effective. In this case, the sideband SUL ′ emphasizing the frequency components ωC−ωL and ωC + ωL close to the resonance frequency ωC of the sideband SUL: SUH (see FIG. 15A) generated by amplitude modulation is set to the same frequency as the carrier. And SUH ′, the frequency characteristics of the ultrasonic radiation of the vibration means 1 can be corrected from the curve B1 to B2 shown in FIG. 15A. As a result, the vibration means 1 can be corrected to a characteristic proportional to the square curve on the side lower than the resonance frequency ωC, and can be corrected to a characteristic inversely proportional to the square curve on the side higher than the resonance frequency ωC. For this purpose, the correction characteristic of the corrector 6 may be a low frequency emphasis characteristic as shown in FIG. 15B.
[0020]
FIG. 16 shows still another embodiment. In this embodiment, a correcting means 6 which is a feature of the embodiment shown in FIG. As a frequency correction characteristic of the correction means 6, a signal input to the vibration means 1 is corrected in advance according to the frequency characteristic of the vibration material 5 in addition to the frequency characteristic of the vibration means 1. Thus, audible vibration having a flat characteristic can be given to the human body. Although FIG. 16 corrects the signal after modulation, it is also effective to apply correction to the input signal before modulation as in the case of FIG.
FIG. 17 shows still another embodiment of the present invention. In this embodiment, it is assumed that there is provided addition means 7 for obtaining a signal obtained by adding the audible signal to the amplitude-modulated inaudible signal shown in FIG.
[0021]
Since the generation of an audible signal due to the non-linear effect of non-audible vibration is a non-linear characteristic, it is very difficult to control the sound quality. 4 and 16, there are cases where the correction means 6 can make the surface flat, but depending on the characteristics of the vibration means 1, the correction means 6 alone may not be able to make corrections. In that case, by mixing the audible signal, it is possible to transmit vibration to the human body in a form that compensates for the audible signal generated by the nonlinear effect. Since the signal in the audible band is controlled only by the linear effect, the control is easier than the non-audible band that is non-linear, and as a result, the sound quality can be controlled more easily. FIG. 18 shows still another embodiment of the present invention, and shows an embodiment in which the correcting means 6 is individually subjected to audible vibration and non-audible modulated vibration. The characteristics of the vibration means 1, the vibration material 5, and the human body are different in frequency characteristics and input / output characteristics in the case of the audible vibration band and the non-audible vibration band. Finer sound quality control is possible. Although FIG. 18 corrects a non-audible signal after modulation, it is also effective to correct an input signal before modulation as in FIGS.
[0022]
19 and 20 show an embodiment in which the electroacoustic transducer according to the present invention is applied to headphones. 19 shown in FIG.19 and FIG.20 shows the electroacoustic transducer by this invention. As described above, the electroacoustic transducer 10 according to the present invention is composed of the vibration means 1 and the vibration material 5 attached to the vibration surface of the vibration means 1.
Reference numeral 11 denotes a headband. By the springs attached to the hinge 12 at both ends of the headband 11 (only one end is shown in the figure), the rotating free end side is always pressed against the portion close to the ear of the wearer. A support rod 14 is further attached to the lever 13, and the electroacoustic transducer 10 is attached to the lower end of the support rod 14. The vibration material 5 attached to the vibration surface is pressed against the skin of the wearer.
[0023]
【The invention's effect】
As described above, according to the present invention, due to the non-linear effect of non-audible vibration, it is possible to efficiently transmit the audible vibration to the human body in a form in which the sound quality is corrected by the vibration means that generates the audible vibration. In addition, the non-audible vibration that generates the nonlinear effect is transmitted to the human body as much as possible, and the nonlinear effect can be caused safely.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining an embodiment of an electroacoustic transducer proposed in the present invention.
FIG. 2 is a diagram for explaining a configuration of a main part of the present invention.
FIG. 3 is a characteristic curve diagram for explaining an example of characteristics of main parts shown in FIG. 2;
FIG. 4 is a block diagram for explaining another embodiment of the electroacoustic transducer proposed in the present invention.
FIG. 5 is a characteristic curve diagram for explaining a frequency characteristic of an audible sound generated by a nonlinear effect of ultrasonic waves.
FIG. 6 is a characteristic curve diagram for explaining frequency characteristics of a general ultrasonic transducer.
FIG. 7 is a characteristic curve diagram showing an example of an equivalent low-frequency characteristic of an excitation unit and an amplitude frequency characteristic of the excitation unit necessary for uttering an audible sound having a flat frequency characteristic without frequency correction.
FIG. 8 is a characteristic curve diagram showing frequency characteristics of a vibration means that can generate audible sound having flat frequency characteristics without frequency correction.
FIG. 9 is a characteristic curve diagram for explaining an actual frequency characteristic of the vibration means.
10 is a characteristic curve diagram for explaining the correction characteristic of the correction means for correcting the frequency characteristic of the vibration means shown in FIG. 9 to the ideal frequency characteristic shown in FIG. 8;
FIG. 11 is a characteristic curve diagram for explaining an example of an input-output characteristic of a vibration means.
12 is a characteristic curve diagram for explaining a correction characteristic for linearizing and correcting the input-to-output characteristic shown in FIG.
13 is a characteristic curve diagram for explaining the result of correcting the input-to-output characteristic of the vibration means shown in FIG. 11 with the correction characteristic shown in FIG. 12;
FIG. 14 is a block diagram for explaining a modified embodiment of the electroacoustic transducer proposed in the present invention.
15 is a characteristic curve diagram for explaining correction characteristics of the embodiment shown in FIG.
FIG. 16 is a block diagram for explaining still another embodiment of the electroacoustic transducer proposed in the present invention.
FIG. 17 is a block diagram for explaining still another embodiment of the electroacoustic transducer proposed in the present invention.
FIG. 18 is a block diagram for explaining still another embodiment of the electroacoustic transducer proposed in the present invention.
FIG. 19 is a front view when the electroacoustic transducer according to the present invention is applied to headphones.
20 is a side view of FIG. 19;
FIG. 21 is a block diagram for explaining a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Excitation means 5 Vibration raw material 2 Ultrasonic signal generation means 6 Frequency correction means 3 Input signal 7 Addition means 4 Amplitude modulation means

Claims

An ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least an audible region;
Modulation means for amplitude-modulating the ultrasonic signal with an audio signal in an audible region to obtain a modulated signal;
Excitation means for generating non-audible vibrations by the modulated signal;
A vibration material that is in contact with the excitation means and has a non-linear characteristic between the contact acceleration and the amplitude of the sound output, which is approximately equal to the acoustic impedance of the human body;
A housing for storing the vibration means with the vibration surface of the vibration means as a surface;
An electroacoustic transducer provided with

An ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least an audible region;
Modulation means for amplitude-modulating the ultrasonic signal with an audio signal in an audible region to obtain a modulated signal;
Excitation means for generating non-audible vibrations by the modulated signal;
From the contact surface of the vibration means so that the acoustic impedance at the contact surface is substantially equal to the acoustic impedance of the vibration means and the acoustic impedance at the surface side is substantially equal to the acoustic impedance of the human body. A vibration material whose acoustic impedance continuously changes to each value over the surface side,
A housing for storing the vibration means with the vibration surface of the vibration means as a surface;
An electroacoustic transducer provided with

An ultrasonic signal generating means for generating an ultrasonic signal having a frequency higher than at least an audible region;
Modulation means for amplitude-modulating the ultrasonic signal with an audio signal in an audible region to obtain a modulated signal;
Excitation means for generating non-audible vibrations by the modulated signal;
In one of the supply path of the modulated signal supplied from the modulation means to the excitation means or the supply path of the audio signal supplied to the modulation means, in a frequency region lower than the resonance frequency of the excitation means, The output frequency characteristic of the non-audible sound of the vibration means is proportional to a value obtained by squaring the difference from the resonance frequency, and in a frequency region higher than the resonance frequency of the vibration means, the vibration means An electroacoustic transducer comprising a correction means for obtaining a frequency correction signal for correcting an output frequency characteristic of a non-audible sound to a characteristic inversely proportional to a value obtained by squaring a difference value from the resonance frequency.

3. The electroacoustic transducer according to claim 1, wherein either a supply path of a modulated signal supplied from the modulation means to the excitation means or a supply path of an audio signal supplied to the modulation means. On the other hand, in a frequency region lower than the resonance frequency of the vibration means, the output frequency characteristic of the non-audible sound of the vibration means is proportional to a value obtained by squaring the value of the difference from the resonance frequency. In a frequency range higher than the resonance frequency of the vibration means, a correction means for obtaining a frequency correction signal for correcting the output frequency characteristic of the non-audible sound of the vibration means to a characteristic inversely proportional to a value obtained by squaring the difference from the resonance frequency. An electroacoustic transducer characterized by comprising:

5. The electroacoustic transducer according to claim 1, wherein the excitation unit is driven by an addition signal obtained by adding the audio signal and the frequency correction signal. 6.