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JP3668187B2 - Sound reproduction method and sound reproduction apparatus - Google Patents

Sound reproduction method and sound reproduction apparatus Download PDF

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Publication number
JP3668187B2
JP3668187B2 JP2001384406A JP2001384406A JP3668187B2 JP 3668187 B2 JP3668187 B2 JP 3668187B2 JP 2001384406 A JP2001384406 A JP 2001384406A JP 2001384406 A JP2001384406 A JP 2001384406A JP 3668187 B2 JP3668187 B2 JP 3668187B2
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frequency
amplitude
signal
audible sound
ultrasonic
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JP2003189387A (en
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健司 清原
正人 三好
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Nippon Telegraph and Telephone Corp
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Nippon Telegraph and Telephone Corp
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Description

【0001】
【発明の属する技術分野】
この発明は各種の拡声装置などに利用することができる音響再生方法及び音響再生装置に関する。
【0002】
【従来の技術】
近年、パーソナルコンピュータを用いたテレビ会議システム(以下デスクトップ会議システム;Desk Top Conference(DTC)システムと呼ぶ)が普及しつつある。これらの会議システムで相手の音声を再生する手段には通常のスピーカを使用していた。
【0003】
【発明が解決しようとする課題】
しかし、通常のスピーカは一般に指向性が広く、TV会議システムを使用している人だけではなく、その周囲にも相手の音声(再生音)が聞こえ、周囲に不要な騒音となって聞こえてしまうという問題があった。これを解決する一つの方法としては可聴音信号で超音波信号を振幅変調し、その振幅変調された超音波を放射して可聴音を再生するというパラメトリックスピーカを用いる方法が考えられる。
【0004】
しかし、パラメトリックスピーカでは超音波素子の共振特性のため高音域及び低音域の再生効率が中音域に比べて低いという問題があった。以下に、その理由を簡単に説明する。
図9は一般的に良く知られているパラメトリックスピーカの概略の構成を示す。パラメトリックスピーカは可聴音信号源1、振幅変調手段2、超音波信号発生手段3、増幅器4、電気音響変換部5とによって構成される。
振幅変調手段2では超音波信号発生手段3から与えられる例えば40KHz程度の周波数を持つ超音波信号USを可聴音信号源1から与えられる可聴音信号ODで振幅変調し、その振幅変調された超音波信号を必要に応じて増幅器4で増幅し、その増幅出力を電気音響変換部5に印加する。電気音響変換部5は複数の超音波振動素子ELで構成され、これら複数の超音波振動素子ELを振幅変調された超音波信号で駆動し、空気中に超音波を放射する。
【0005】
空気中に放射された超音波は空気の非線形性による自己復調作用によって可聴音を生成する。
ここで、振幅変調手段2が両側波変調方式の振幅変調器であるものとすると、振幅変調された被変調信号は図10に示すように、超音波信号USの周波数ωoをキャリア周波数とし、そのキャリア周波数ωoの上側と下側に上側波帯SBUと、下側波帯SBDが発生する。可聴音信号ODの下限周波数をωL、上限周波数をωHとすると、上側波帯SBUの下限周波数はωo+ωL、上限周波数はωo+ωHとなる。また、下側波帯SBDの下限周波数はωo−ωH、上限周波数はωo−ωLとなる。
【0006】
一方、超音波の自己復調作用により生成される可聴音の音圧には図11に示すように可聴周波数帯域内(ωL〜ωH)において周波数ωの2乗(ω2)に正比例する周波数特性が与えられる。この周波数特性は、上側波帯SBUと下側波帯SBDの双方に対して図10に破線で示すように低域成分ωo+ωL及びωo−ωL側を抑圧する特性として作用する。
従って、本来であればイコライザ等により可聴音信号ODの低域成分ωLから高域成分ωHにかけて1/ω2の特性で周波数補正し、この周波数補正した可聴音信号を振幅変調手段2に入力する必要があるが、従来より、この不都合を解消する一つの方法として超音波振動素子ELの共振特性RSを共振周波数ωoより下側の周波数領域では上記可聴音信号ODにおける周波数の二乗特性に相当する次の特性f(ω)で減衰させ、
f(ω)={ωL/(ωo−ω)}2 (ωo−ωH≦ω≦ωo−ωL)
但し、f(ω)は周波数ωo−ωLに於ける利得に対する減衰率を表す。
共振周波数ωoより上側の周波数領域では、次の特性g(ω)とすることにより、イコライザ無しで再生される可聴音の音圧の周波数特性を平坦な周波数特性に補正する方法が採られている。
【0007】
g(ω)={ωL/(ω−ωo)}2 (ωo+ωL≦ω≦ωo+ωH)
但し、g(ω)は周波数ωo+ωLに於ける利得に対する減衰率を表す。
図12に一般的な超音波振動素子の超音波放射振幅特性を示す。共振周波数ωoより下側の周波数領域A1では上記特性f(ω)で減衰する領域DW1を有し、共振周波数ωoより上側の周波数領域A2には特性g(ω)で減衰する領域DW2が存在する。図10に示した超音波信号USの周波数を図12に示した共振周波数ωoに一致させてこの超音波振動素子を駆動したとすると、減衰領域DW1とDW2の範囲内の周波数領域A1及びA2では超音波の自己復調作用によって生成される可聴音の音圧の周波数特性(ω2)は減衰特性DW1とDW2の特性に従って相殺され可聴音の音圧の生成特性を平坦な周波数特性に補正することができる。
【0008】
然し乍ら、普通一般の超音波振動素子では共振周波数ωoの近傍に減衰領域DW1、DW2の特性から外れた平坦部Xが存在する。この平坦部Xの存在により超音波によって生成される可聴音の低域成分は超音波の自己復調作用によって生成される可聴音の音圧の周波数特性(ω2)の影響を受け、生成レベルが低下する現象が発生する。
この現象を図12と図13を用いて説明する。図12に示した超音波振動素子の共振特性RSにおいて、平坦部Xの上限及び下限までの周波数をω1とすると、平坦部Xの下限周波数はωo−ω1、上限周波数はωo+ω1となる。ω1が例えば1KHzの場合、図10に示した振幅変調された超音波信号に含まれる下側波帯SBDと上側波帯SBUの各成分の中で1KHzより高い可聴信号成分は超音波振動素子の減衰領域DW1とDW2の傾斜特性により補正され、図13に示す平坦な周波数特性Bで可聴音が生成される。
【0009】
これに対し、下側波帯SBDと上側波帯SBUに含まれる1KHzより低い可聴信号成分は減衰領域DW1とDW2の範囲外であるため、1KHzより低い可聴信号成分の周波数特性は周波数補正がされず、超音波の自己復調作用によって生成される可聴音の音圧に与えられる周波数特性(ω2)に従って漸次低下する特性を呈する(図13曲線C)。この不都合を解消するには超音波振動素子の共振特性を図12に破線で示すように、共振周波数ωoまで減衰領域DW1及びDW2が延長された特性の超音波振動素子を用いれば1KHzより低い可聴信号成分は図13に示す曲線Dの特性で再生されるが、このような特性の超音波振動素子を得ることは難しい。
【0010】
以上は低域側で発生する不都合に関して説明したが、高域側でも高域成分の生成レベルが低下する不都合が存在する。その理由としては図10に示した下側波帯SBDと上側波帯SBUの含まれる高域成分ωHは超音波信号USの周波数ωoから最も離れた周波数に位置する。このため、図12に示した超音波放射振幅特性を持つ超音波振動素子を共振周波数ωoに超音波信号USの周波数とを一致させて駆動した場合、下側波帯SBDと上側波帯SBUに含まれる高域成分ωHは超音波放射効率の悪い周波数領域で駆動されることになる。高域成分ωH側は超音波の自己復調作用により生成される可聴音の音圧の周波数特性(ω2)によって強調されるが、超音波振動素子の放射効率の悪い周波数領域で駆動されることにより、結果的に高域側の生成レベルも低下する第2の不都合が生じる。
この発明の目的は低域側及び高域側の双方を中音域と同等のレベルで再生することができる音響再生方法及び音響再生装置を提案しようとするものである。
【0011】
【課題を解決するための手段】
この発明では、共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部を可聴音信号により入力超音波信号を振幅変調した超音波信号により駆動し、可聴音を再生する音響再生方法において、可聴音信号を所定の可聴音周波数より低い低域成分と所定の可聴音周波数より高い高域成分にろ波し低域成分と高域成分により超音波信号を各々単側波形式で振幅変調し、上限周波数より高い減衰領域又は下限周波数より低い減衰領域を超音波信号を可聴音信号の低域成分で振幅変調した信号の帯域とし、平坦部の領域を超音波信号を可聴音信号の高域成分で振幅変調した信号の帯域としたことを特徴とする音響再生方法を提案する。
【0012】
また、この発明の音響再生方法において、可聴音信号の低域成分で入力超音波信号より低い周波数の単側波に振幅変調した場合は可聴音信号の高域成分で入力超音波信号より高い周波数の単側波に振幅変調し、上記可聴音信号の低域成分で入力超音波信号より高い周波数の単側波に振幅変調した場合は可聴音信号の高域成分で振幅変調手段により入力超音波信号より低い周波数の単側波に振幅変調することを特徴とする音響再生方法を提案する。
更にこの発明では、共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部と、下限周波数の近傍の周波数に合致した超音波信号を発生する超音波信号発生手段と、可聴音信号を所定の可聴音周波数より低い低域成分と所定の可聴音周波数より高い高域成分にろ波するろ波手段と、このろ波手段でろ波した可聴音信号の低域成分により超音波信号発生手段が発生する超音波信号を下側波帯の単側波が得られる振幅変調形式で振幅変調する第1振幅変調器と、ろ波手段でろ波した可聴信号の高域成分により超音波信号発生手段が発生する超音波信号を上側波帯の単側波が得られる振幅変調形式で振幅変調する第2振幅変調器と、これら第1振幅変調器及び第2振幅変調器で単側波形式で振幅変調された超音波信号を加算し、その加算した超音波信号を電気音響変換部に印加する加算手段とによって構成したことを特徴とする音響再生装置を提案する。
【0013】
更にこの発明では、共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部と、上限周波数の近傍の周波数に合致した超音波信号を発生する超音波信号発生手段と、可聴音信号を所定の可聴音周波数より低い低域成分と所定の可聴音周波数より高い高域成分にろ波するろ波手段と、このろ波手段でろ波した可聴音信号の低域成分により超音波信号発生手段が発生する超音波信号を上側波帯の単側波が得られる振幅変調形式で振幅変調する第1振幅変調器と、ろ波手段でろ波した可聴信号の高域成分により超音波信号発生手段が発生する超音波信号を下側波帯の単側波が得られる振幅変調形式で振幅変調する第2振幅変調器と、これら第1振幅変調器及び第2振幅変調器で単側波形式で振幅変調された超音波信号を加算し、その加算した超音波信号を電気音響変換部に印加する加算手段とによって構成したことを特徴とする音響再生装置を提案する。
【0014】
作用
この発明による音響再生方法及び音響再生装置によれば、可聴音信号を低域成分と高域成分に分離し、これら低域成分と高域成分を単側波帯変調方式の振幅変調器で振幅変調すると共に、超音波信号の周波数(キャリア周波数)を超音波振動素子の平坦部Xの下限周波数又は上限周波数に合致させ、これにより低域成分によって発生する単側波帯を超音波振動素子の減衰特性を呈する周波数領域に配置し、高域成分によって発生する単側波帯を超音波振動素子の平坦部に配置して超音波振動素子を駆動するから、低域成分の全部が超音波振動素子の共振特性の減衰領域により周波数特性が補正され可聴音信号の低域側の全帯域が平坦な周波数特性で可聴音として再生される。
また、可聴音の高域側の成分は超音波振動素子の周波数特性に存在する平坦部Xの周波数領域に近づけて駆動するから、高域側の放射効率が向上し、可聴音の高域成分も効率よく再生することができる利点が得られる。
【0015】
【発明の実施の形態】
図1にこの発明の一実施例を示す。図中1は可聴音信号源を示す。この発明ではこの可聴音信号源1が出力する可聴音信号ODを帯域ろ波器11と12に供給し、可聴音信号ODを低域成分と高域成分に分離する。
帯域ろ波器11は可聴音信号ODから低域成分LOWをろ波し、帯域ろ波器12は可聴音信号ODから高域成分HIをろ波する。可聴音信号ODの周波数帯域がωL〜ωHであるものとし、更に、電気音響変換部5に用いられる超音波振動素子ELの共振特性が、図2に示す周波数特性であるものとすると、帯域ろ波器11は図3に曲線BP1で示すように、可聴音信号ODの下限周波数ωLから所定の周波数ωMまでの周波数成分(ωL〜ωM)をろ波し、可聴音信号ODの低域成分LOWを出力する。一方、帯域ろ波器12は図3に曲線BP2で示すように周波数成分(ωM〜ωH)をろ波し、可聴音信号ODの高域成分HIを出力する。
【0016】
帯域ろ波器11と12でろ波した可聴音信号ODの低域成分LOWと高域成分HIを単側波変調方式の第1及び第2振幅変調器13と14に入力し、超音波信号発生手段3から入力される超音波信号USを可聴音信号の低域成分LOWと高域成分HIとで単側波変調方式で振幅変調する。
ここで、超音波信号発生手段3から第1及び第2振幅変調器13と14に入力する超音波信号USの周波数を超音波振動素子ELの平坦部Xの、ここでは下限周波数ωo−ω1(以下にこの周波数をωCと表記する)に一致させる。更に、この場合可聴音信号ODの低域成分LOWで超音波信号USを振幅変調する第1振幅変調器13は下側波帯を発生する単側波変調方式であるものとする。更に、第2振幅変調器14は周波数ωCの超音波信号USを可聴音信号ODの高域成分HIで振幅変調し、上側波を発生する振幅変調器を用いる。
【0017】
上記の条件で振幅変調した被変調信号の周波数分布を図4と図5に示す。図4は低域成分LOWで超音波信号USを振幅変調し、下側波帯SBLOWを得た結果を示す。下側波帯SBLOWは下限側がωC−ωMの周波数成分を有し、上限側にωC−ωLの周波数成分を有する。ωL=20Hz,ωM=1KHzとすれば下側波帯SBLOWの帯域幅は980Hzである。
図5は高域成分HIで超音波信号USを振幅変調し、上側波帯SBHIを得た結果を示す。上側波帯SBHIの上限周波数はωC+ωH、下限周波数はωC+ωMとなる。その帯域幅はこの例では(ωC+ωH)−(ωC+ωM)=20KHz−1KHz=19KHzである。
【0018】
振幅変調により得られた下側波帯SBLOWと上側波帯SBHIはろ波器15と16で帯域制限して取り出され、加算器17で加算し、増幅器18で増幅して電気音響変換部5に印加し、電気音響変換部5から超音波として放射させることにより、下側波帯SBLOWと上側波帯SBHIに含まれる可聴音信号ODの低域成分LOWと高域成分HIを可聴音として再生することができる。
ここで、超音波信号USの周波数ωCを超音波振動素子ELの共振特性RSの平坦部Xの下限周波数ωo−ω1に合致させたから、低域成分LOWで超音波信号USを振幅変調して得た下側波帯SBLOWの全帯域を超音波振動素子ELの共振特性RSの下側の減衰領域DW1に含ませることができる。
【0019】
この結果、可聴音信号ODの低域成分LOWは共振特性RSの減衰領域DW1によって周波数特性が補正され、ωL〜ωM=20Hz〜1KHzまでの全ての帯域を平坦な周波数特性で可聴音として再生することができる。
一方、高域成分HIで超音波信号USを振幅変調して得た上側波帯SBHIはその下限周波数ωC+ωMは実質的に超音波振動素子ELの共振周波数ωoにほぼ一致し、この共振周波数ωoから帯域幅がほぼ19KHzで上限周波数ωC+ωHが配置されるため、図10で説明した従来の両側波帯変調方式の場合の上限周波数ωo+ωHより共振周波数ωoにω1の周波数分だけ近づけることができる。
【0020】
この結果、高域成分HIは超音波振動素子ELの応答性の良い周波数領域で駆動することができるため、少ない駆動電力で従来と同等の強度の超音波を放出させることができる利点が得られる。
図6に単側波帯変調方式の振幅変調器13及び14の概略の構成を示す。単側波帯変調方式の振幅変調器13及び14は、増幅器Mと、90°移相器φ1、φ2と、2台の乗算器MU1、MU2と、2台の加算器ADD1、ADD2とによって構成される。可聴音信号源1、超音波信号発生手段3において各々可聴音信号cosΩt、超音波信号cosωotが発生した場合を考える。両者はそれぞれ90°移相器φ1、φ2で90°移相して−sinΩt、−sinωotとなり、乗算器MU1で互いに乗算されて振幅変調信号sinΩt sinωotが得られる。一方、乗算器MU2では可聴音信号cosΩt、超音波信号cosωotが互いに乗算されて振幅変調信号cosΩt cosωotが得られる。
【0021】
ここで、共振周波数ωoより高い周波数の単側波帯を示す周波数ωo+Ωの成分cos(ωo+Ω){=cosΩt cosωot−sinΩt sinωot}を得るには加算器ADD2において振幅変調信号cosΩt cosωotの極性を正に、振幅変調信号sinΩt sinωotの極性を負にする。
ここで、共振周波数ωoより低い周波数の単側波帯を示す周波数ωo−Ωの成分cos(ωo−Ω){=cosΩt cosωot+sinΩt sinωot}を得るには加算器ADD2において振幅変調信号cosΩt cosωot、振幅変調信号sinΩt sinωotともに極性を正にする。尚、ADD1は上側波信号或いは下側波信号と共に超音波信号cosωotを空中放射し、超音波の自己復調作用を発生させるための加算器である。
【0022】
図7及び図8は可聴音信号ODの低域成分LOWで超音波信号USを振幅変調器13及び14(図1参照)で振幅変調する場合に、低域成分LOWの変調結果として上側波帯SB´LOWを得るようにし、高域成分HIの変調結果として下側波帯SB´HIを得るように構成した場合の各被変調信号の周波数分布を示す。
この場合、超音波信号USの周波数ωCは超音波振動素子ELの平坦部Xの上限周波数ωo+ω1に一致させる。従って、低域成分LOWで超音波信号USを振幅変調して得られる上側波帯SB´LOWの下限周波数はωC+ωL、上限周波数はωC+ωMとなり、その帯域幅はこの例ではωL=20Hz、ω1=1KHzとすると、1KHz−20Hz=980Hzである。
【0023】
また、高域成分HIで超音波信号USを振幅変調して得られる下側波帯SB´HIの下限周波数はωC−ωH、上限周波数はωC−ωMとなり、その帯域幅はこの例ではωH=20KHz、ω1=1KHzとした場合19KHzとなる。
従って、この場合も低域成分LOWを含む上側波帯SB´LOWは帯域幅が980Hzとすると超音波振動素子ELの共振特性RSの上側の減衰特性DW2の範囲に納めることができる。すなわち、低域成分LOWを上側波帯SB´LOWとして振幅変調した場合でも、低域成分LOWの全帯域を共振特性RSの減衰特性DW2により可聴音の再生周波数特性を平坦な特性に補正することができる。
【0024】
また、高域成分HIで超音波信号USを振幅変調して得られた下側波帯SB´HIも下限周波数がωC−ωHであるため、この場合のωCはωo+ω1であるから、実質的にはωo+ω1−ωHであるため、下限周波数をω1の周波数分だけ共振周波数ωoに近づけることができる。この結果、高域成分HIにより超音波振動素子ELを応答性の良い周波数帯域で駆動することができる利点が得られる。
尚、上述では帯域ろ波器11と12で1KHzを境にωM=1KHz以下を低域成分LOW、1KHz以上を高域成分HIとしてろ波したが、この1KHzの値は超音波振動素子ELの共振特性に応じて選定される値であり、特にこの1KHzに限定されるものでないことは容易に理解できよう。
【0025】
【発明の効果】
以上説明したように、この発明によれば超音波信号を可聴音信号によって振幅変調し、この振幅変調された超音波信号によって超音波振動子によって構成される電気音響振動素子を駆動し、超音波により可聴音を再生する音響再生方法において、超音波振動子が共振周波数の近傍に平坦部Xを具備していたとしても、その平坦部Xの存在によって発生する可聴音の再生周波数特性が低域側で減衰し、低域成分の音が再生し難かった欠点を解消することができる。
【0026】
また、高域成分も、高域成分を含む帯域の全体が超音波振動素子の共振周波数ω0に近づく方向に偏倚されて超音波振動素子を駆動するから、超音波振動素子のレスポンスの良い周波数領域で駆動するため、高域成分も効率よく再生することができる利点が得られる。
【図面の簡単な説明】
【図1】この発明による音響再生方法を実現するための音響再生装置の一実施例を説明するためのブロック図。
【図2】図1に示した電気音響変換部に用いた超音波振動素子の共振特性曲線を説明するための特性曲線図。
【図3】図1に示した帯域ろ波器のろ波特性を説明するための特性曲線図。
【図4】この発明の要部の動作を説明するための信号成分の周波数分布を説明するための特性曲線図。
【図5】図4と同様の特性曲線図。
【図6】図1に示した実施例に用いた単側波帯変調方式の振幅変調器の概要を説明するためのブロック図。
【図7】この発明の変形実施例を説明するための特性曲線図。
【図8】図7と同様の特性曲線図。
【図9】従来の技術を説明するためのブロック図。
【図10】従来の技術に用いられている両側波帯変調方式の振幅変調によって得られる被変調信号の周波数成分の分布を説明するための特性曲線図。
【図11】超音波の自己復調作用によって再生される可聴音の音圧に与えられる周波数特性を説明するための特性曲線図。
【図12】従来の技術で発生する不都合を説明するための特性曲線図。
【図13】図12と同様の特性曲線図。
【符号の説明】
1 可聴音信号源 14 第2振幅変調器
5 電気音響変換部 15、16 ろ波器
EL 超音波振動素子 17 加算器
11、12 帯域ろ波器 18 増幅器
13 第1振幅変調器
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an acoustic reproduction method and an acoustic reproduction apparatus that can be used for various types of loudspeakers.
[0002]
[Prior art]
In recent years, a video conference system using a personal computer (hereinafter referred to as a desktop conference system; referred to as a “Desk Top Conference (DTC) system) is becoming widespread. In these conference systems, a normal speaker is used as means for reproducing the voice of the other party.
[0003]
[Problems to be solved by the invention]
However, ordinary speakers generally have a wide directivity, and not only the person using the TV conference system but also the other party's voice (reproduced sound) can be heard around them, and they can be heard as unnecessary noise around them. There was a problem. As one method for solving this, a method using a parametric speaker in which an ultrasonic signal is amplitude-modulated with an audible sound signal and the audible sound is reproduced by emitting the amplitude-modulated ultrasonic wave can be considered.
[0004]
However, the parametric speaker has a problem that the reproduction efficiency in the high sound range and the low sound range is lower than that in the mid sound range due to the resonance characteristics of the ultrasonic element. The reason will be briefly described below.
FIG. 9 shows a schematic configuration of a generally well-known parametric speaker. The parametric speaker includes an audible sound signal source 1, an amplitude modulation means 2, an ultrasonic signal generation means 3, an amplifier 4, and an electroacoustic conversion unit 5.
In the amplitude modulation means 2, the ultrasonic signal US having a frequency of, for example, about 40 KHz given from the ultrasonic signal generation means 3 is amplitude-modulated with the audible sound signal OD given from the audible sound signal source 1, and the amplitude-modulated ultrasonic wave The signal is amplified by the amplifier 4 as necessary, and the amplified output is applied to the electroacoustic converter 5. The electroacoustic conversion unit 5 includes a plurality of ultrasonic vibration elements EL, drives the plurality of ultrasonic vibration elements EL with an amplitude-modulated ultrasonic signal, and radiates ultrasonic waves into the air.
[0005]
The ultrasonic wave radiated into the air generates an audible sound by the self-demodulation action due to the nonlinearity of the air.
Here, if the amplitude modulation means 2 is a double-sided modulation type amplitude modulator, the amplitude-modulated modulated signal has a frequency ωo of the ultrasonic signal US as a carrier frequency as shown in FIG. An upper sideband SBU and a lower sideband SBD are generated above and below the carrier frequency ωo. When the lower limit frequency of the audible sound signal OD is ωL and the upper limit frequency is ωH, the lower limit frequency of the upper sideband SBU is ωo + ωL, and the upper limit frequency is ωo + ωH. The lower limit frequency of the lower sideband SBD is ωo−ωH, and the upper limit frequency is ωo−ωL.
[0006]
On the other hand, the sound pressure of the audible sound generated by the self-demodulation action of ultrasonic waves has a frequency characteristic that is directly proportional to the square of the frequency ω (ω 2 ) within the audible frequency band (ωL to ωH) as shown in FIG. Given. This frequency characteristic acts as a characteristic that suppresses the low frequency components ωo + ωL and ωo−ωL sides as shown by broken lines in FIG. 10 for both the upper sideband SBU and the lower sideband SBD.
Therefore, if the frequency is corrected by a characteristic of 1 / ω 2 from the low frequency component ωL to the high frequency component ωH of the audible sound signal OD by an equalizer or the like, this frequency-corrected audible sound signal is input to the amplitude modulation means 2. Conventionally, as one method for solving this inconvenience, the resonance characteristic RS of the ultrasonic vibration element EL corresponds to the square characteristic of the frequency in the audible sound signal OD in the frequency region below the resonance frequency ωo. It is attenuated by the following characteristic f (ω),
f (ω) = {ωL / (ωo−ω)} 2 (ωo−ωH ≦ ω ≦ ωo−ωL)
Here, f (ω) represents the attenuation rate with respect to the gain at the frequency ωo−ωL.
In the frequency region above the resonance frequency ωo, a method is adopted in which the frequency characteristic of the sound pressure of the audible sound reproduced without an equalizer is corrected to a flat frequency characteristic by using the following characteristic g (ω). .
[0007]
g (ω) = {ωL / (ω−ωo)} 2 (ωo + ωL ≦ ω ≦ ωo + ωH)
However, g (ω) represents the attenuation rate with respect to the gain at the frequency ωo + ωL.
FIG. 12 shows ultrasonic radiation amplitude characteristics of a general ultrasonic vibration element. The frequency region A1 below the resonance frequency ωo has a region DW1 that attenuates with the characteristic f (ω), and the frequency region A2 above the resonance frequency ωo has a region DW2 that attenuates with the property g (ω). . If this ultrasonic vibration element is driven by making the frequency of the ultrasonic signal US shown in FIG. 10 coincide with the resonance frequency ωo shown in FIG. 12, in the frequency regions A1 and A2 within the range of the attenuation regions DW1 and DW2. The frequency characteristic (ω 2 ) of the sound pressure of the audible sound generated by the self-demodulation action of the ultrasonic wave is canceled according to the characteristics of the attenuation characteristics DW1 and DW2, and the sound pressure generation characteristic of the audible sound is corrected to a flat frequency characteristic. Can do.
[0008]
However, in an ordinary ordinary ultrasonic transducer, there is a flat portion X that deviates from the characteristics of the attenuation regions DW1 and DW2 in the vicinity of the resonance frequency ωo. The low frequency component of the audible sound generated by the ultrasonic wave due to the presence of the flat portion X is affected by the frequency characteristic (ω 2 ) of the sound pressure of the audible sound generated by the self-demodulation action of the ultrasonic wave, and the generation level is The phenomenon of decreasing occurs.
This phenomenon will be described with reference to FIGS. In the resonance characteristic RS of the ultrasonic vibration element shown in FIG. 12, when the frequency up to the upper limit and the lower limit of the flat portion X is ω1, the lower limit frequency of the flat portion X is ωo−ω1, and the upper limit frequency is ωo + ω1. For example, when ω1 is 1 KHz, the audible signal component higher than 1 KHz among the components of the lower sideband SBD and the upper sideband SBU included in the amplitude-modulated ultrasonic signal shown in FIG. Corrected by the slope characteristics of the attenuation regions DW1 and DW2, audible sound is generated with a flat frequency characteristic B shown in FIG.
[0009]
On the other hand, since the audible signal component lower than 1 KHz included in the lower sideband SBD and the upper sideband SBU is outside the range of the attenuation regions DW1 and DW2, the frequency characteristic of the audible signal component lower than 1 KHz is frequency-corrected. First, it exhibits a characteristic that gradually decreases according to the frequency characteristic (ω 2 ) given to the sound pressure of the audible sound generated by the self-demodulation action of the ultrasonic wave (curve C in FIG. 13). In order to eliminate this inconvenience, as shown by the broken line in FIG. 12, the resonance characteristic of the ultrasonic vibration element is audible lower than 1 KHz by using the ultrasonic vibration element having a characteristic in which the attenuation regions DW1 and DW2 are extended to the resonance frequency ωo. The signal component is reproduced with the characteristic of the curve D shown in FIG. 13, but it is difficult to obtain an ultrasonic vibration element having such a characteristic.
[0010]
The above has described the inconvenience occurring on the low frequency side, but there is also a disadvantage that the generation level of the high frequency component is lowered on the high frequency side. The reason is that the high frequency component ωH included in the lower sideband SBD and the upper sideband SBU shown in FIG. 10 is located at a frequency farthest from the frequency ωo of the ultrasonic signal US. For this reason, when the ultrasonic vibration element having the ultrasonic radiation amplitude characteristic shown in FIG. 12 is driven so that the resonance frequency ωo matches the frequency of the ultrasonic signal US, the lower sideband SBD and the upper sideband SBU are driven. The included high frequency component ωH is driven in a frequency region where the ultrasonic radiation efficiency is poor. The high frequency component ωH side is emphasized by the frequency characteristic (ω 2 ) of the sound pressure of the audible sound generated by the self-demodulation action of the ultrasonic wave, but it is driven in the frequency region where the radiation efficiency of the ultrasonic vibration element is poor. As a result, there arises a second disadvantage that the generation level on the high frequency side also decreases.
An object of the present invention is to propose an acoustic reproduction method and an acoustic reproduction apparatus capable of reproducing both the low-frequency side and the high-frequency side at a level equivalent to that of the middle sound range.
[0011]
[Means for Solving the Problems]
In the present invention, the output amplitude characteristic has a flat portion with a predetermined bandwidth straddling the resonance frequency, and at least one of the regions having a frequency higher than the upper limit frequency or lower than the lower limit frequency of the bandwidth than the flat portion. In an acoustic reproduction method for reproducing an audible sound by driving an electroacoustic transducer having an attenuation characteristic in which an output amplitude characteristic is attenuated by an ultrasonic signal obtained by amplitude-modulating an input ultrasonic signal with an audible sound signal, the audible sound signal is predetermined. Filters the low frequency component lower than the audible sound frequency and the high frequency component higher than the predetermined audible sound frequency, and modulates the amplitude of the ultrasonic signal with each of the low frequency component and the high frequency component with a single-side waveform, and is higher than the upper limit frequency. The attenuation region or the attenuation region lower than the lower limit frequency is the band of the signal obtained by modulating the amplitude of the ultrasonic signal with the low frequency component of the audible sound signal, and the flat region is the amplitude of the ultrasonic signal with the high frequency component of the audible sound signal. Proposes an acoustic playback method being characterized in that the bandwidth of the tone signal.
[0012]
Further, in the sound reproduction method of the present invention, when the amplitude modulation is performed on the low frequency component of the audible sound signal to a single side wave having a lower frequency than the input ultrasonic signal, the high frequency component of the audible sound signal is higher than the input ultrasonic signal. When the amplitude is modulated to a single side wave having a higher frequency than the input ultrasonic signal by the low frequency component of the audible sound signal, the input ultrasonic wave is input by the amplitude modulation means with the high frequency component of the audible sound signal. A sound reproduction method is proposed in which amplitude modulation is performed to a single side wave having a frequency lower than that of a signal.
Further, according to the present invention, the output amplitude characteristic has a flat portion with a predetermined bandwidth across the resonance frequency, and the flat portion is in at least one of a region having a frequency higher than the upper limit frequency or lower than the lower limit frequency of the bandwidth. An electroacoustic transducer having an attenuation characteristic in which the output amplitude characteristic is attenuated, an ultrasonic signal generating means for generating an ultrasonic signal matching a frequency near the lower limit frequency, and an audible sound signal from a predetermined audible sound frequency An ultrasonic signal generated by an ultrasonic signal generating means by a filtering means for filtering a low-frequency component and a high-frequency component higher than a predetermined audible sound frequency, and an audible sound signal filtered by the filtering means. An ultrasonic signal generated by the ultrasonic signal generating means by the first amplitude modulator for amplitude-modulating the single side wave of the lower sideband in the form of amplitude modulation and the high frequency component of the audible signal filtered by the filtering means The upper wave A second amplitude modulator that performs amplitude modulation in an amplitude modulation format that provides a single side wave, and an ultrasonic signal that is amplitude-modulated with a single-side waveform type by the first amplitude modulator and the second amplitude modulator, and A sound reproducing device is proposed which is constituted by adding means for applying the added ultrasonic signal to an electroacoustic transducer.
[0013]
Further, according to the present invention, the output amplitude characteristic has a flat portion with a predetermined bandwidth across the resonance frequency, and the flat portion is in at least one of a region having a frequency higher than the upper limit frequency or lower than the lower limit frequency of the bandwidth. An electroacoustic transducer having an attenuation characteristic that attenuates the output amplitude characteristic, an ultrasonic signal generating means for generating an ultrasonic signal that matches a frequency near the upper limit frequency, and an audible sound signal from a predetermined audible sound frequency. An ultrasonic signal generated by an ultrasonic signal generating means by a filtering means for filtering a low-frequency component and a high-frequency component higher than a predetermined audible sound frequency, and an audible sound signal filtered by the filtering means. An ultrasonic signal generated by the ultrasonic signal generating means by a first amplitude modulator that modulates the amplitude of the audible signal in an amplitude modulation format that can obtain a single sideband of the upper sideband, and a high frequency component of the audible signal filtered by the filtering means Lower side wave A second amplitude modulator that performs amplitude modulation in an amplitude modulation format that provides a single side wave, and an ultrasonic signal that is amplitude-modulated with a single-side waveform type by the first amplitude modulator and the second amplitude modulator, and A sound reproducing device is proposed which is constituted by adding means for applying the added ultrasonic signal to an electroacoustic transducer.
[0014]
According to the sound reproducing method and a sound reproducing apparatus according to the action <br/> this invention, an audible sound signal is separated into low frequency components and high frequency components, these low-frequency components and high-frequency component of the single sideband modulation method Amplitude modulation is performed by the amplitude modulator, and the frequency (carrier frequency) of the ultrasonic signal is matched with the lower limit frequency or the upper limit frequency of the flat portion X of the ultrasonic vibration element, thereby generating a single sideband generated by a low frequency component. It is arranged in the frequency domain that exhibits the attenuation characteristics of the ultrasonic vibration element, and the single sideband generated by the high frequency component is arranged on the flat part of the ultrasonic vibration element to drive the ultrasonic vibration element. All the frequency characteristics are corrected by the attenuation region of the resonance characteristics of the ultrasonic vibration element, and the entire low frequency band of the audible sound signal is reproduced as an audible sound with a flat frequency characteristic.
In addition, since the high frequency component of the audible sound is driven close to the frequency region of the flat portion X existing in the frequency characteristics of the ultrasonic vibration element, the high frequency radiation efficiency is improved and the high frequency component of the audible sound is improved. In addition, there is an advantage that it can be efficiently reproduced.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes an audible sound signal source. In the present invention, the audible sound signal OD output from the audible sound signal source 1 is supplied to the bandpass filters 11 and 12, and the audible sound signal OD is separated into a low frequency component and a high frequency component.
The band filter 11 filters the low frequency component LOW from the audible sound signal OD, and the band filter 12 filters the high frequency component HI from the audible sound signal OD. Assuming that the frequency band of the audible sound signal OD is ωL to ωH and that the resonance characteristics of the ultrasonic vibration element EL used in the electroacoustic transducer 5 are the frequency characteristics shown in FIG. As shown by a curve BP1 in FIG. 3, the wave filter 11 filters the frequency components (ωL to ωM) from the lower limit frequency ωL of the audible sound signal OD to the predetermined frequency ωM, and the low frequency component LOW of the audible sound signal OD. Is output. On the other hand, the bandpass filter 12 filters the frequency components (ωM to ωH) as shown by a curve BP2 in FIG. 3, and outputs the high frequency component HI of the audible sound signal OD.
[0016]
The low-frequency component LOW and high-frequency component HI of the audible sound signal OD filtered by the bandpass filters 11 and 12 are input to the first and second amplitude modulators 13 and 14 of the single side wave modulation method, and an ultrasonic signal is generated. The ultrasonic signal US input from the means 3 is amplitude-modulated by the single side wave modulation method with the low frequency component LOW and the high frequency component HI of the audible sound signal.
Here, the frequency of the ultrasonic signal US inputted from the ultrasonic signal generating means 3 to the first and second amplitude modulators 13 and 14 is set to the flat portion X of the ultrasonic vibration element EL, here the lower limit frequency ωo−ω1 ( Hereinafter, this frequency is expressed as ωC). Further, in this case, the first amplitude modulator 13 that modulates the amplitude of the ultrasonic signal US with the low frequency component LOW of the audible sound signal OD is assumed to be a single side modulation method that generates a lower sideband. Further, the second amplitude modulator 14 uses an amplitude modulator that modulates the amplitude of the ultrasonic signal US having the frequency ωC with the high frequency component HI of the audible sound signal OD and generates an upper wave.
[0017]
FIG. 4 and FIG. 5 show the frequency distribution of the modulated signal amplitude-modulated under the above conditions. FIG. 4 shows the result of amplitude modulation of the ultrasonic signal US with the low frequency component LOW to obtain the lower sideband SB LOW . The lower sideband SB LOW has a frequency component of ωC−ωM on the lower limit side and a frequency component of ωC−ωL on the upper limit side. If ωL = 20 Hz and ωM = 1 KHz, the bandwidth of the lower sideband SB LOW is 980 Hz.
FIG. 5 shows the result of amplitude modulation of the ultrasonic signal US with the high frequency component HI to obtain the upper sideband SB HI . The upper limit frequency of the upper sideband SB HI is ωC + ωH, and the lower limit frequency is ωC + ωM. In this example, the bandwidth is (ωC + ωH) − (ωC + ωM) = 20 KHz-1 KHz = 19 KHz.
[0018]
The lower side band SB LOW and the upper side band SB HI obtained by the amplitude modulation are taken out with band limiting by the filters 15 and 16, added by the adder 17, amplified by the amplifier 18, and amplified by the electroacoustic conversion unit 5. And the low frequency component LOW and the high frequency component HI of the audible sound signal OD included in the lower side band SB LOW and the upper side band SB HI are radiated as an ultrasonic wave from the electroacoustic transducer 5. Can be played as.
Here, since the frequency ωC of the ultrasonic signal US is matched with the lower limit frequency ωo−ω1 of the flat portion X of the resonance characteristic RS of the ultrasonic vibration element EL, the ultrasonic signal US is obtained by amplitude-modulating the low-frequency component LOW. Further, the entire lower band SB LOW can be included in the lower attenuation region DW1 of the resonance characteristic RS of the ultrasonic transducer EL.
[0019]
As a result, the frequency characteristic of the low frequency component LOW of the audible sound signal OD is corrected by the attenuation region DW1 of the resonance characteristic RS, and all bands from ωL to ωM = 20 Hz to 1 KHz are reproduced as audible sounds with flat frequency characteristics. be able to.
On the other hand, the high frequency component HI ultrasonic signal upper sideband obtained by amplitude modulating the US SB HI is the lower limit frequency .omega.C + .omega.M substantially substantially coincides with the resonance frequency ωo of the ultrasonic vibration element EL, the resonant frequency ωo Since the upper limit frequency ωC + ωH is arranged with a bandwidth of about 19 KHz, the resonance frequency ωo can be made closer to the resonance frequency ωo by the frequency of ω1 than the upper limit frequency ωo + ωH in the case of the conventional double sideband modulation method described in FIG.
[0020]
As a result, the high-frequency component HI can be driven in a frequency region with good responsiveness of the ultrasonic vibration element EL, so that there is an advantage that ultrasonic waves having the same intensity as the conventional one can be emitted with a small driving power. .
FIG. 6 shows a schematic configuration of single sideband modulation type amplitude modulators 13 and 14. The single sideband modulation type amplitude modulators 13 and 14 include an amplifier M, 90 ° phase shifters φ1 and φ2, two multipliers MU1 and MU2, and two adders ADD1 and ADD2. Is done. Consider a case where an audible sound signal cosΩt and an ultrasonic signal cosωot are generated in the audible sound signal source 1 and the ultrasonic signal generation means 3, respectively. Both are 90 ° phase shifted by 90 ° phase shifters φ1 and φ2 to become −sinΩt and −sinωot, respectively, and are multiplied by a multiplier MU1 to obtain an amplitude modulation signal sinΩt sinωot. On the other hand, the multiplier MU2 multiplies the audible sound signal cosΩt and the ultrasonic signal cosωot with each other to obtain an amplitude modulation signal cosΩt cosωot.
[0021]
Here, in order to obtain the component cos (ωo + Ω) {= cosΩt cosωot−sinΩt sinωot} of the frequency ωo + Ω indicating a single sideband having a frequency higher than the resonance frequency ωo, the polarity of the amplitude modulation signal cosΩt cosωot is made positive in the adder ADD2. The polarity of the amplitude modulation signal sinΩt sinωot is made negative.
Here, in order to obtain the component cos (ωo−Ω) {= cosΩt cosωot + sinΩt sinωot} of the frequency ωo−Ω indicating a single sideband having a frequency lower than the resonance frequency ωo, the adder ADD2 uses the amplitude modulation signal cosΩt cosωot and amplitude modulation. Both signals sinΩt and sinωot are positive in polarity. Note that ADD1 is an adder for emitting the ultrasonic signal cosωot together with the upper side wave signal or the lower side wave signal in the air to generate an ultrasonic self-demodulation action.
[0022]
7 and 8 show the upper sideband as the modulation result of the low frequency component LOW when the amplitude of the ultrasonic signal US is modulated by the amplitude modulators 13 and 14 (see FIG. 1) with the low frequency component LOW of the audible sound signal OD. The frequency distribution of each modulated signal in the case where SB ′ LOW is obtained and the lower sideband SB ′ HI is obtained as the modulation result of the high frequency component HI is shown.
In this case, the frequency ωC of the ultrasonic signal US is matched with the upper limit frequency ωo + ω1 of the flat portion X of the ultrasonic vibration element EL. Therefore, the lower limit frequency of the upper sideband SB ′ LOW obtained by amplitude modulating the ultrasonic signal US with the low frequency component LOW is ωC + ωL, the upper limit frequency is ωC + ωM, and the bandwidths are ωL = 20 Hz and ω1 = 1 kHz in this example. Then, 1 KHz-20 Hz = 980 Hz.
[0023]
The lower limit frequency of the lower sideband SB' HI obtained by amplitude-modulated ultrasonic signal US in the high-frequency component HI is .omega.C-.omega.H, the upper limit frequency .omega.C-.omega.M next, the bandwidth in this example .omega.H = When 20 KHz and ω1 = 1 KHz, the frequency is 19 KHz.
Accordingly, in this case as well, the upper side band SB ′ LOW including the low frequency component LOW can be within the range of the attenuation characteristic DW2 above the resonance characteristic RS of the ultrasonic vibration element EL when the bandwidth is 980 Hz. That is, even when the low frequency component LOW is amplitude-modulated with the upper side band SB ′ LOW , the reproduction frequency characteristic of the audible sound is corrected to a flat characteristic by the attenuation characteristic DW2 of the resonance characteristic RS for the entire low frequency band LOW. Can do.
[0024]
Further, since the lower sideband SB ′ HI obtained by amplitude-modulating the ultrasonic signal US with the high frequency component HI also has a lower limit frequency of ωC−ωH, ωC in this case is ωo + ω1. Since ωo + ω1-ωH, the lower limit frequency can be made closer to the resonance frequency ωo by the frequency of ω1. As a result, there is an advantage that the ultrasonic vibration element EL can be driven in a frequency band with good responsiveness by the high frequency component HI.
In the above description, the band-pass filters 11 and 12 are filtered with ωM = 1 KHz or less as the low-frequency component LOW and 1 KHz or more as the high-frequency component HI with 1 KHz as the boundary. The value of 1 KHz is the value of the ultrasonic vibration element EL. It can be easily understood that the value is selected according to the resonance characteristics and is not particularly limited to 1 KHz.
[0025]
【The invention's effect】
As described above, according to the present invention, an ultrasonic signal is amplitude-modulated by an audible sound signal, an electroacoustic vibration element constituted by an ultrasonic transducer is driven by the amplitude-modulated ultrasonic signal, In the sound reproduction method for reproducing the audible sound by the above, even if the ultrasonic vibrator has the flat portion X near the resonance frequency, the reproduction frequency characteristic of the audible sound generated by the presence of the flat portion X is low. It is possible to eliminate the disadvantage that the low frequency component sound is difficult to reproduce.
[0026]
In addition, the high-frequency component also drives the ultrasonic vibration element so that the entire band including the high-frequency component is biased in a direction approaching the resonance frequency ω 0 of the ultrasonic vibration element. Since driving is performed in a region, there is an advantage that high frequency components can be efficiently reproduced.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining an embodiment of a sound reproducing device for realizing a sound reproducing method according to the present invention.
FIG. 2 is a characteristic curve diagram for explaining a resonance characteristic curve of an ultrasonic vibration element used in the electroacoustic transducer shown in FIG.
FIG. 3 is a characteristic curve diagram for explaining the filtering characteristics of the bandpass filter shown in FIG. 1;
FIG. 4 is a characteristic curve diagram for explaining the frequency distribution of signal components for explaining the operation of the main part of the present invention.
5 is a characteristic curve diagram similar to FIG.
6 is a block diagram for explaining the outline of the single sideband modulation type amplitude modulator used in the embodiment shown in FIG. 1; FIG.
FIG. 7 is a characteristic curve diagram for explaining a modified embodiment of the present invention.
FIG. 8 is a characteristic curve diagram similar to FIG.
FIG. 9 is a block diagram for explaining a conventional technique.
FIG. 10 is a characteristic curve diagram for explaining the distribution of frequency components of a modulated signal obtained by amplitude modulation using a double sideband modulation method used in the prior art.
FIG. 11 is a characteristic curve diagram for explaining frequency characteristics given to sound pressure of audible sound reproduced by self-demodulation action of ultrasonic waves.
FIG. 12 is a characteristic curve diagram for explaining inconveniences occurring in the conventional technique.
13 is a characteristic curve diagram similar to FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Audible sound signal source 14 2nd amplitude modulator 5 Electroacoustic conversion part 15, 16 Filter EL Ultrasonic vibration element 17 Adder 11, 12 Band filter 18 Amplifier 13 1st amplitude modulator

Claims (4)

共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に前記平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部を可聴音信号により入力超音波信号を振幅変調した超音波信号により駆動し、可聴音を再生する音響再生方法において、
上記可聴音信号を所定の可聴音周波数より低い低域成分と前記所定の可聴音周波数より高い高域成分にろ波し上記低域成分と高域成分により超音波信号を各々単側波形式で振幅変調し、上記上限周波数より高い減衰領域又は下限周波数より低い減衰領域を上記超音波信号を上記可聴音信号の低域成分で振幅変調した信号の帯域とし、上記平坦部の領域を上記超音波信号を上記可聴音信号の高域成分で振幅変調した信号の帯域としたことを特徴とする音響再生方法。
It has a flat portion of the output amplitude characteristic with a predetermined bandwidth across the resonance frequency, and the output amplitude is higher than the flat portion in at least one of the frequency range higher than the upper limit frequency of the bandwidth or lower than the lower limit frequency. In an acoustic reproduction method of reproducing an audible sound by driving an electroacoustic transducer having an attenuation characteristic whose characteristic is attenuated by an ultrasonic signal obtained by amplitude-modulating an input ultrasonic signal with an audible sound signal,
The audible sound signal is filtered into a low-frequency component lower than a predetermined audible sound frequency and a high-frequency component higher than the predetermined audible sound frequency, and the ultrasonic signal is respectively converted into a single-side waveform by the low-frequency component and the high-frequency component. The amplitude modulation is performed, and the attenuation region higher than the upper limit frequency or the attenuation region lower than the lower limit frequency is set as the band of the signal obtained by amplitude-modulating the ultrasonic signal with the low frequency component of the audible sound signal, and the flat region is the ultrasonic wave. A sound reproduction method characterized in that the signal is a signal band amplitude-modulated by a high frequency component of the audible sound signal.
請求項1記載の音響再生方法において、上記可聴音信号の低域成分で前記入力超音波信号より低い周波数の単側波に振幅変調した場合は上記可聴音信号の高域成分で前記入力超音波信号より高い周波数の単側波に振幅変調し、
上記可聴音信号の低域成分で前記入力超音波信号より高い周波数の単側波に振幅変調した場合は上記可聴音信号の高域成分で上記振幅変調手段により前記入力超音波信号より低い周波数の単側波に振幅変調することを特徴とする音響再生方法。
2. The sound reproducing method according to claim 1, wherein when the amplitude of the low frequency component of the audible sound signal is amplitude-modulated to a single side wave having a frequency lower than that of the input ultrasonic signal, the input ultrasonic wave is detected with the high frequency component of the audible sound signal. Amplitude modulation to a single side wave of higher frequency than the signal,
When amplitude modulation is performed on a single side wave having a higher frequency than the input ultrasonic signal with a low-frequency component of the audible sound signal, the amplitude modulation means has a frequency lower than that of the input ultrasonic signal with the high-frequency component of the audible sound signal. An acoustic reproduction method, wherein amplitude modulation is performed on a single side wave.
共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に前記平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部と、
上記下限周波数の近傍の周波数に合致した超音波信号を発生する超音波信号発生手段と、
可聴音信号を所定の可聴音周波数より低い低域成分と前記所定の可聴音周波数より高い高域成分にろ波するろ波手段と、
このろ波手段でろ波した可聴音信号の低域成分により上記超音波信号発生手段が発生する超音波信号を下側波帯の単側波が得られる振幅変調形式で振幅変調する第1振幅変調器と、
上記ろ波手段でろ波した可聴信号の高域成分により上記超音波信号発生手段が発生する超音波信号を上側波帯の単側波が得られる振幅変調形式で振幅変調する第2振幅変調器と、
これら第1振幅変調器及び第2振幅変調器で単側波形式で振幅変調された超音波信号を加算し、その加算した超音波信号を上記電気音響変換部に印加する加算手段と、
によって構成したことを特徴とする音響再生装置。
It has a flat portion of the output amplitude characteristic with a predetermined bandwidth across the resonance frequency, and the output amplitude is higher than the flat portion in at least one of the frequency range higher than the upper limit frequency of the bandwidth or lower than the lower limit frequency. An electroacoustic transducer having an attenuation characteristic that attenuates the characteristic;
Ultrasonic signal generating means for generating an ultrasonic signal that matches a frequency in the vicinity of the lower limit frequency;
Filtering means for filtering the audible sound signal into a low frequency component lower than a predetermined audible sound frequency and a high frequency component higher than the predetermined audible sound frequency;
The first amplitude modulation that modulates the ultrasonic signal generated by the ultrasonic signal generating means by the low frequency component of the audible sound signal filtered by the filtering means in an amplitude modulation format that can obtain a single sideband of the lower sideband. And
A second amplitude modulator for amplitude-modulating the ultrasonic signal generated by the ultrasonic signal generating means by the high-frequency component of the audible signal filtered by the filtering means in an amplitude modulation format in which an upper side band single side wave is obtained; ,
Adding means for adding ultrasonic signals amplitude-modulated with a single-side waveform type by the first amplitude modulator and the second amplitude modulator, and applying the added ultrasonic signals to the electroacoustic converter;
A sound reproduction device characterized by comprising:
共振周波数を跨ぐ所定の帯域幅で出力振幅特性の平坦部を有し、当該帯域幅の上限周波数より高い周波数か下限周波数より低い周波数の領域のうち少なくとも何れか一方に前記平坦部よりも出力振幅特性が減衰する減衰特性を有する電気音響変換部と、
上記上限周波数の近傍の周波数に合致した超音波信号を発生する超音波信号発生手段と、
可聴音信号を所定の可聴音周波数より低い低域成分と前記所定の可聴音周波数より高い高域成分にろ波するろ波手段と、
このろ波手段でろ波した可聴音信号の低域成分により上記超音波信号発生手段が発生する超音波信号を上側波帯の単側波が得られる振幅変調形式で振幅変調する第1振幅変調器と、
上記ろ波手段でろ波した可聴信号の高域成分により上記超音波信号発生手段が発生する超音波信号を下側波帯の単側波が得られる振幅変調形式で振幅変調する第2振幅変調器と、
これら第1振幅変調器及び第2振幅変調器で単側波形式で振幅変調された超音波信号を加算し、その加算した超音波信号を上記電気音響変換部に印加する加算手段と、
によって構成したことを特徴とする音響再生装置。
It has a flat portion of the output amplitude characteristic with a predetermined bandwidth across the resonance frequency, and the output amplitude is higher than the flat portion in at least one of the frequency range higher than the upper limit frequency of the bandwidth or lower than the lower limit frequency. An electroacoustic transducer having an attenuation characteristic that attenuates the characteristic;
An ultrasonic signal generating means for generating an ultrasonic signal matching a frequency in the vicinity of the upper limit frequency;
Filtering means for filtering the audible sound signal into a low frequency component lower than a predetermined audible sound frequency and a high frequency component higher than the predetermined audible sound frequency;
A first amplitude modulator that modulates the ultrasonic signal generated by the ultrasonic signal generating means by the low frequency component of the audible sound signal filtered by the filtering means in an amplitude modulation format that provides a single side wave in the upper side band. When,
A second amplitude modulator for amplitude-modulating the ultrasonic signal generated by the ultrasonic signal generating means by the high-frequency component of the audible signal filtered by the filtering means in an amplitude modulation format in which a single side wave in the lower sideband is obtained. When,
Adding means for adding ultrasonic signals amplitude-modulated with a single-side waveform type by the first amplitude modulator and the second amplitude modulator, and applying the added ultrasonic signals to the electroacoustic converter;
A sound reproduction device characterized by comprising:
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