JP3785718B2 - Sound playback device - Google Patents

Sound playback device Download PDF

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Publication number
JP3785718B2
JP3785718B2 JP3757497A JP3757497A JP3785718B2 JP 3785718 B2 JP3785718 B2 JP 3785718B2 JP 3757497 A JP3757497 A JP 3757497A JP 3757497 A JP3757497 A JP 3757497A JP 3785718 B2 JP3785718 B2 JP 3785718B2
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JP
Japan
Prior art keywords
signal
reproduction
speaker
microphone
external noise
Prior art date
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JP3757497A
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Japanese (ja)
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JPH10234095A (en
Inventor
文靖 今野
信一 大木
由男 中村
敏彦 大橋
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Panasonic Corp
Panasonic Holdings Corp
Original Assignee
Panasonic Corp
Matsushita Electric Industrial Co Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は、特に車載用に好適な音響再生装置に関するものである。
【０００２】
【従来の技術】
図６に従来の音響再生装置のブロック図を示しており、図６において、ＣＤプレーヤ、ラジオ受信機、テープレコーダ等の信号源１からの再生信号は減算器２を介して電力増幅器３に入力されて電力増幅され、上記電力増幅器３からの信号出力はスピーカ４に入力されて再生される。
【０００３】
一方、上記スピーカ４の周辺にはマイクロフォン５が配置されており、このマイクロフォン５により上記スピーカ４による再生音成分とスピーカ周囲の１００Ｈｚ程度以下の外来ノイズ成分を集音する。
【０００４】
このマイクロフォン５からの出力信号はマイクロフォン増幅器６にて増幅されて上記減算器２に帰還されることにより、再生音場での外来ノイズ成分を減衰させるように作用する。
【０００５】
【発明が解決しようとする課題】
しかしながら、従来の音響再生装置においては、マイクロフォン増幅器６により外来ノイズ成分ＶNと再生音成分ＶMとを再生信号に対して帰還させるため、外来ノイズ成分のみならず再生音成分も低い帯域において減少してしまい、図７の破線に示すように再生周波数特性のバランスがくずれてしまうという問題があった。
【０００６】
本発明は、帰還ループにより外来ノイズ成分を減衰するも再生周波数のバランスのくずれのない音響再生装置を提供することを目的とする。
【０００７】
【課題を解決するための手段】
この課題を解決するために本発明は、マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、このノイズ検出手段の出力により上記再生系に設けた可変フィルタのフィルタ特性を可変するように構成したものである。
【０００８】
これにより、外来ノイズ成分のみを減衰させ、かつ再生周波数のバランスのくずれのない音響再生装置を提供することができる。
【０００９】
【発明の実施の形態】
本発明の請求項１記載の発明は、信号源からの再生信号を増幅する電力増幅器と、この電力増幅器からの信号出力を再生するスピーカとを含む再生系と、このスピーカの周辺に配置され、上記スピーカによる再生音成分とスピーカ周囲の外来ノイズ成分を収音するマイクロフォンと、上記電力増幅器の入力側に設けられ、上記再生信号より上記マイクロフォンからの出力信号を減算し外来ノイズ成分を減衰する減算器とを含む帰還系とを備え、上記マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、このノイズ検出手段の出力により上記再生系に設けた可変フィルタのフィルム特性を可変するように構成した音響再生装置であり、再生周波数のバランスのくずれなく外来ノイズ成分を減衰するという作用を有する。
【００１０】
本発明の請求項２記載の発明は、信号源からの再生信号を増幅する電力増幅器と、この電力増幅器からの信号出力を再生するスピーカとを含む再生系と、このスピーカの周辺に配置され、上記スピーカによる再生成分とスピーカ周囲の外来ノイズ成分を収音するマイクロフォンと、上記電力増幅器の入力側に設けられ、上記再生信号より上記マイクロフォンからの出力信号を減算し外来ノイズ成分を減衰する減算器とを含む帰還系とを備え、上記帰還系を外来ノイズ成分の大きさに応じて帰還量を可変するよう構成し、かつ上記再生系に帰還伝達関数の逆特性を有する可変フィルタを設け、上記マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、上記可変フィルタを上記外来ノイズ成分の大きさに応じてフィルタ特性を可変するよう構成した音響再生装置であり、外来ノイズ成分の大きさに応じて帰還量を変化し、その帰還量に対応してフィルタ特性を変化させて外来ノイズ成分に応じた再生周波数特性を補正するという作用を有する。
【００１１】
以下、本発明の実施の形態を説明する。
【００１２】
なお、まず本願発明に至る改善例について説明する。
【００１３】
（改善例１）
図１は音響再生装置の改善例におけるブロック図を示す。図１において、１１はＣＤプレーヤ、ラジオ受信機、テープレコーダ等の信号源であり、この信号源１１からの再生信号は減算器１２に入力される。上記減算器１２は後述するマイクロフォン１５からの出力信号と上記再生信号とを減算処理し、その出力を電力増幅器１３に入力して電力増幅する。上記電力増幅器１３からの信号出力はスピーカ１４に入力されて再生される。上記スピーカ１４の周辺にはマイクロフォン１５が配置されており、上記マイクロフォン１５により上記スピーカ１４による再生音成分ＶMとスピーカ周囲の外来ノイズ成分ＶNを集音する。このマイクロフォン１５からの出力信号はマイクロフォン増幅器１６にて増幅されて上記減算器１２に入力されることにより、再生信号に対して負帰還される。ここで、上記減算器１２の前段にはフィルタ１７が設けられており、再生信号を当該フィルタ１７を介して上記減算器１２に加えるように構成されている。
【００１４】
いま、信号源１１からの再生信号をＶin、フィルタ１７の特性をＴF、減算器１２の出力をＶo／Ａ、電力増幅器１３の増幅度をＡ、電力増幅器１３の出力をＶo、スピーカ１４の特性をＴsp、スピーカ１４の再生出力をＶM、外来ノイズをＶNとすると、マイクロフォン１５の出力信号はＶN＋ＶMとなり、ＶN＋ＶoＴspと変換される。したがって、減算器１２の出力Ｖo／Ａは
Ｖo／Ａ＝ＶinＴF−（ＶN＋ＶoＴsp） （式１）
となり、電力増幅器１３の出力Ｖoは、
Ｖo＝ＡＶinＴF−ＡＶN−ＡＶoＴsp （式２）
Ｖo（１＋ＡＴsp）＝ＡＶinＴF−ＡＶN （式３）
Ｖo＝（Ａ／１＋ＡＴsp）ＴFＶin−（Ａ／１＋ＡＴsp）ＶN （式４）
となる。ここで、フィルタ１７の特性ＴFは
ＴF＝（１＋ＡＴsp）／Ａ （式５）
と設定するならば、電力増幅器１３の出力Ｖoは
Ｖo＝Ｖin−（Ａ／１＋ＡＴsp）・ＶN （式６）
となる。このようにフィルタ１７の特性を図２の実線に示すように帰還伝達関数の逆特性とすることにより、図７の実線に示すようにスピーカ１４により再生される出力の再生周波数特性はフラットなものとなり、外来ノイズＶNを減衰させると同時に周波数バラツキのないように特性補正することができる。
【００１５】
（実施の形態１）
図３は本発明の一実施の形態における音響再生装置のブロック図を示す。図３において、１１は信号源であり、この信号源１１からの再生信号は減算器１２に入力される。上記減算器１２は後述するマイクロフォン１５からの出力信号にもとづく制御信号と上記再生信号とを減算処理し、その出力を電力増幅器１３に入力して電力増幅する。上記電力増幅器１３からの信号出力はスピーカ１４に入力されて再生される。
【００１６】
上記スピーカ１４の周辺にはマイクロフォン１５が配置されており、上記マイクロフォン１５により上記スピーカ１４による再生音成分ＶMとスピーカ周囲の外来ノイズ成分ＶNを集音する。このマイクロフォン１５からの出力信号はマイクロフォン増幅器１６にて増幅されて上記減算器１２に負帰還される。
【００１７】
ここで、上記信号源１１からの再生信号はスピーカ等価フィルタ２０を介して第２の減算器２１の一方の入力端に入力され、上記マイクロフォン増幅器１６の出力信号は上記第２の減算器２１の他方の入力端に入力されて減算処理されることにより、上記第２の減算器２１より外来ノイズ成分ＶNのみの信号を取り出す。この外来ノイズ成分のみに起因する信号はＡＣ／ＤＣ変換器２２に入力され、検波、積分の処理がなされて上記ＡＣ／ＤＣ変換器２２より制御電圧が出力される。
【００１８】
上記ＡＣ／ＤＣ変換器２２からの制御電圧は上記マイクロフォン増幅器１６と上記減算器１２との間に設けた電圧制御増幅器１９に加えられて当該電圧制御増幅器１９のゲインを制御することにより、上記減算器１２に負帰還されるマイクロフォン増幅器１６からの出力信号の大きさを変化させる。一方、上記ＡＣ／ＤＣ変換器２２からの制御電圧は上記信号源１１と上記減算器１２との間に設けた電圧制御フィルタ１８に加えられて当該電圧制御フィルタ１８の特性を変化させる。したがって、上記マイクロフォン１５に入力された外来ノイズ成分に連動して上記マイクロフォン１５から減算器１２への帰還ループの帰還量を変化させると同時に信号源１１からの再生信号に対する再生周波数特性の補正を自動的に行うことができる。
【００１９】
具体的には、第２の減算器２１の出力すなわち外来ノイズ成分がない場合には図４の実線に示すように電圧制御増幅器１９のゲインをＧ0とし、図５の実線に示すように電圧制御フィルタ１８の特性を決定したとすると、第２の減算器２１の出力すなわち外来ノイズ成分が大きくなるに従い、図４の破線及び一点鎖線に示すように電圧制御増幅器１９のゲインをＧ1，Ｇ2とし、この時、上記電圧制御フィルタ１８のフィルタ特性を図５の破線および一点鎖線に示すように変化させる。ここで、上記電圧制御フィルタ１８のフィルタ特性は帰還ループの帰還伝達関数の逆特性を有する。
【００２０】
【発明の効果】
以上のように本発明によれば、マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、このノイズ検出手段の出力により上記再生系に設けた可変フィルタのフィルタ特性を可変するように構成したので、外来ノイズを減衰させるべく設けた帰還ループに起因する再生周波数特性のバラツキを抑え、再生周波数のバランスのくずれなく外来ノイズの影響を減衰することができる。
【図面の簡単な説明】
【図１】 本発明に至る改善例の音響再生装置を示すブロック図
【図２】 同装置に使用されるフィルタの特性図
【図３】 本発明の一実施の形態における音響再生装置を示すブロック図
【図４】 同装置に使用される電圧制御増幅器の特性図
【図５】 同装置に使用される電圧制御フィルタの特性図
【図６】 従来の音響再生装置を示すブロック図
【図７】 同装置の再生周波数特性図
【符号の説明】
１，１１ 信号源
２，１２ 減算器
３，１３ 電力増幅器
４，１４ スピーカ
５，１５ マイクロフォン
６，１６ マイクロフォン増幅器
１７ フィルタ
１８ 電圧制御フィルタ
１９ 電圧制御増幅器
２０ スピーカ等価フィルタ
２１ 第２の減算器
２２ ＡＣ／ＤＣ変換器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sound reproducing apparatus particularly suitable for in-vehicle use.
[0002]
[Prior art]
FIG. 6 shows a block diagram of a conventional sound reproduction apparatus. In FIG. 6, a reproduction signal from a signal source 1 such as a CD player, a radio receiver, or a tape recorder is input to a power amplifier 3 via a subtractor 2. Then, the power is amplified, and the signal output from the power amplifier 3 is input to the speaker 4 and reproduced.
[0003]
On the other hand, a microphone 5 is disposed around the speaker 4, and the microphone 5 collects a reproduced sound component from the speaker 4 and an external noise component of about 100 Hz or less around the speaker.
[0004]
The output signal from the microphone 5 is amplified by the microphone amplifier 6 and fed back to the subtractor 2 so that the external noise component in the reproduction sound field is attenuated.
[0005]
[Problems to be solved by the invention]
However, in the conventional sound reproducing device, the external noise component V N and the reproduced sound component V M are fed back to the reproduction signal by the microphone amplifier 6, so that not only the external noise component but also the reproduced sound component is reduced in a low band. As a result, there is a problem in that the reproduction frequency characteristics are unbalanced as indicated by the broken line in FIG.
[0006]
An object of the present invention is to provide a sound reproducing apparatus that attenuates an external noise component by a feedback loop but does not cause a balance in reproduction frequency.
[0007]
[Means for Solving the Problems]
In order to solve this problem, the present invention provides noise detection means for subtracting the output signal from the microphone and the reproduction signal from the signal source to extract only the external noise component, and the reproduction by the output of the noise detection means. The filter characteristic of the variable filter provided in the system is configured to be variable .
[0008]
As a result, it is possible to provide an acoustic reproduction device that attenuates only the external noise component and does not lose the balance of the reproduction frequency .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The invention of claim 1, wherein the present invention, a power amplifier for amplifying a reproduced signal from the signal source, and a reproduction system including a loudspeaker for reproducing a signal output from the power amplifier, are disposed around the speaker, A microphone that picks up the reproduced sound component from the speaker and the external noise component around the speaker, and a subtractor that is provided on the input side of the power amplifier and subtracts the output signal from the microphone from the reproduced signal to attenuate the external noise component A noise detection means for extracting only the external noise component by subtracting the output signal from the microphone and the reproduction signal from the signal source, and providing the reproduction by the output of the noise detection means. This is a sound reproduction device configured to vary the film characteristics of the variable filter provided in the system, and the balance of the reproduction frequency is not lost. It has the effect of attenuating the coming noise component.
[0010]
The invention according to claim 2 of the present invention is disposed in the periphery of the speaker, including a power amplifier that amplifies the reproduced signal from the signal source, a speaker that reproduces the signal output from the power amplifier, and the speaker. A microphone that collects the reproduction component by the speaker and the external noise component around the speaker, and a subtractor provided on the input side of the power amplifier, and subtracts the output signal from the microphone from the reproduction signal to attenuate the external noise component and a feedback system including bets, the feedback system configured to vary the feedback amount according to the magnitude of the external noise component, and provided with a variable filter having an inverse characteristic of the feedback transfer function to the reproducing system, the noise detecting means for extracting only an external noise component provided by subtracting the reproduction signal from the output signal and the signal source from the microphone, the variable filter This sound reproduction device is configured to vary the filter characteristics according to the magnitude of the external noise component. The feedback amount is changed according to the magnitude of the external noise component, and the filter characteristic is changed according to the feedback amount. Thus, the reproduction frequency characteristic corresponding to the external noise component is corrected.
[0011]
Hereinafter, the embodiments of the present invention to explain.
[0012]
First, an improvement example leading to the present invention will be described.
[0013]
( Improvement example 1)
Figure 1 shows a block diagram of an improvement example of acoustic reproducing apparatus. In FIG. 1, reference numeral 11 denotes a signal source such as a CD player, a radio receiver, or a tape recorder. A reproduction signal from the signal source 11 is input to a subtracter 12. The subtractor 12 subtracts an output signal from a microphone 15 described later and the reproduction signal, and inputs the output to the power amplifier 13 to amplify the power. The signal output from the power amplifier 13 is input to the speaker 14 and reproduced. The periphery of the speaker 14 is disposed a microphone 15, collects external noise component V N of the reproduced sound component V M and the speaker around by the speaker 14 by the microphone 15. The output signal from the microphone 15 is amplified by the microphone amplifier 16 and input to the subtractor 12, thereby being negatively fed back to the reproduction signal. Here, a filter 17 is provided in the preceding stage of the subtractor 12, and the reproduction signal is added to the subtractor 12 through the filter 17.
[0014]
Now, the reproduced signal from the signal source 11 is V in , the characteristic of the filter 17 is T F , the output of the subtractor 12 is V o / A, the amplification degree of the power amplifier 13 is A, the output of the power amplifier 13 is V o , characteristic T sp speaker 14, the reproduction output V M of the speaker 14, when the external noise and V N, the output signal of the microphone 15 is V N + V M becomes, is transformed V N + V o T sp. Accordingly, the output V o / A of the subtracter 12 is V o / A = V in T F - (V N + V o T sp) ( Equation 1)
The output V o of the power amplifier 13 is
V o = AV in TF −AV N −AV o T sp (Formula 2)
V o (1 + AT sp ) = AV in TF −AV N (Formula 3)
V o = (A / 1 + AT sp) T F V in - (A / 1 + AT sp) V N ( Equation 4)
It becomes. Here, the characteristic T F of the filter 17 is T F = (1 + AT sp ) / A (Formula 5)
Is set, the output V o of the power amplifier 13 is V o = V in − (A / 1 + AT sp ) · V N (Equation 6)
It becomes. Thus, by setting the characteristic of the filter 17 to the inverse characteristic of the feedback transfer function as shown by the solid line in FIG. 2, the reproduction frequency characteristic of the output reproduced by the speaker 14 is flat as shown by the solid line in FIG. Thus, the external noise V N can be attenuated and at the same time the characteristics can be corrected so that there is no frequency variation.
[0015]
(Embodiment 1 )
FIG. 3 is a block diagram of the sound reproducing device according to the embodiment of the present invention. In FIG. 3, reference numeral 11 denotes a signal source, and a reproduction signal from the signal source 11 is input to the subtractor 12. The subtractor 12 subtracts a control signal based on an output signal from a microphone 15 described later and the reproduction signal, and inputs the output to the power amplifier 13 to amplify the power. The signal output from the power amplifier 13 is input to the speaker 14 and reproduced.
[0016]
The periphery of the speaker 14 is disposed a microphone 15, collects external noise component V N of the reproduced sound component V M and the speaker around by the speaker 14 by the microphone 15. The output signal from the microphone 15 is amplified by the microphone amplifier 16 and negatively fed back to the subtractor 12.
[0017]
Here, the reproduction signal from the signal source 11 is input to one input terminal of the second subtracter 21 via the speaker equivalent filter 20, and the output signal of the microphone amplifier 16 is the output of the second subtractor 21. By inputting to the other input terminal and performing subtraction processing, a signal of only the external noise component V N is taken out from the second subtractor 21. A signal resulting from only the external noise component is input to the AC / DC converter 22, subjected to detection and integration processing, and a control voltage is output from the AC / DC converter 22.
[0018]
The control voltage from the AC / DC converter 22 is applied to a voltage control amplifier 19 provided between the microphone amplifier 16 and the subtractor 12 to control the gain of the voltage control amplifier 19, thereby performing the subtraction. The magnitude of the output signal from the microphone amplifier 16 negatively fed back to the amplifier 12 is changed. On the other hand, the control voltage from the AC / DC converter 22 is applied to the voltage control filter 18 provided between the signal source 11 and the subtractor 12 to change the characteristics of the voltage control filter 18. Accordingly, the feedback amount characteristic of the reproduction signal from the signal source 11 is automatically corrected at the same time as the feedback amount of the feedback loop from the microphone 15 to the subtracter 12 is changed in conjunction with the external noise component input to the microphone 15. Can be done automatically.
[0019]
Specifically, when there is no output from the second subtractor 21, that is, no external noise component, the gain of the voltage control amplifier 19 is G 0 as shown by the solid line in FIG. 4, and the voltage as shown by the solid line in FIG. Assuming that the characteristics of the control filter 18 are determined, the gain of the voltage control amplifier 19 is set to G 1 , G 1 as indicated by the broken line and the alternate long and short dash line in FIG. 4 as the output of the second subtracter 21, that is, the external noise component increases. 2, and at this time, to change the filter characteristics of the voltage controlled filter 18 as shown in broken lines and one-dot chain line in FIG. Here, the filter characteristic of the voltage control filter 18 has an inverse characteristic of the feedback transfer function of the feedback loop.
[0020]
【The invention's effect】
As described above , according to the present invention, there is provided noise detection means for extracting only the external noise component by subtracting the output signal from the microphone and the reproduction signal from the signal source, and the reproduction system is provided by the output of the noise detection means. Because the filter characteristics of the variable filter provided in the above are made variable , the fluctuation of the reproduction frequency characteristic caused by the feedback loop provided to attenuate the external noise is suppressed, and the influence of the external noise can be achieved without causing the balance of the reproduction frequency. Can be attenuated.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a sound reproducing apparatus of an improved example leading to the present invention. FIG. 2 is a characteristic diagram of a filter used in the apparatus. FIG. 3 is a block diagram showing the sound reproducing apparatus according to an embodiment of the present invention. FIG. 4 is a characteristic diagram of a voltage control amplifier used in the device. FIG. 5 is a characteristic diagram of a voltage control filter used in the device. FIG. 6 is a block diagram showing a conventional sound reproducing device. Reproduction frequency characteristic diagram of the device [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,11 Signal source 2,12 Subtractor 3,13 Power amplifier 4,14 Speaker 5,15 Microphone 6,16 Microphone amplifier 17 Filter 18 Voltage control filter 19 Voltage control amplifier 20 Speaker equivalent filter 21 2nd subtractor 22 AC / DC converter

Claims (2)

信号源からの再生信号を増幅する電力増幅器と、この電力増幅器からの信号出力を再生するスピーカとを含む再生系と、このスピーカの周辺に配置され、上記スピーカによる再生音成分とスピーカ周囲の外来ノイズ成分を収音するマイクロフォンと、上記電力増幅器の入力側に設けられ、上記再生信号より上記マイクロフォンからの出力信号を減算し外来ノイズ成分を減衰する減算器とを含む帰還系とを備え、上記マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、このノイズ検出手段の出力により上記再生系に設けた可変フィルタのフィルム特性を可変するように構成した音響再生装置。  A reproduction system including a power amplifier that amplifies a reproduction signal from a signal source, and a speaker that reproduces a signal output from the power amplifier, and a reproduction sound component by the speaker and an external environment around the speaker. A feedback system including a microphone that picks up a noise component, and a subtractor that is provided on the input side of the power amplifier and subtracts an output signal from the microphone from the reproduction signal to attenuate an external noise component; A noise detection means for extracting only the external noise component by subtracting the output signal from the microphone and the reproduction signal from the signal source is provided, and the film characteristic of the variable filter provided in the reproduction system is variable by the output of the noise detection means. A sound reproducing device configured to do so. 信号源からの再生信号を増幅する電力増幅器と、この電力増幅器からの信号出力を再生するスピーカとを含む再生系と、このスピーカの周辺に配置され、上記スピーカによる再生成分とスピーカ周囲の外来ノイズ成分を収音するマイクロフォンと、上記電力増幅器の入力側に設けられ、上記再生信号より上記マイクロフォンからの出力信号を減算し外来ノイズ成分を減衰する減算器とを含む帰還系とを備え、上記帰還系を外来ノイズ成分の大きさに応じて帰還量を可変するよう構成し、かつ上記再生系に帰還伝達関数の逆特性を有する可変フィルタを設け、上記マイクロフォンからの出力信号と上記信号源からの再生信号を減算して外来ノイズ成分のみを抽出するノイズ検出手段を設け、上記可変フィルタを上記外来ノイズ成分の大きさに応じてフィルタ特性を可変するよう構成した音響再生装置。A reproduction system including a power amplifier that amplifies a reproduction signal from a signal source and a speaker that reproduces a signal output from the power amplifier, and a reproduction component by the speaker and external noise around the speaker arranged around the speaker A feedback system including a microphone that picks up a component and a subtractor that is provided on the input side of the power amplifier and subtracts an output signal from the microphone from the reproduction signal to attenuate an external noise component; The system is configured to vary the feedback amount according to the magnitude of the external noise component, and a variable filter having an inverse characteristic of a feedback transfer function is provided in the reproduction system, and the output signal from the microphone and the signal source subtracts the reproduced signal provided noise detecting means for extracting only the external noise component, respond to the variable filter to the magnitude of the external noise component Sound reproducing apparatus configured so as to vary the filter characteristic Te.
JP3757497A 1997-02-21 1997-02-21 Sound playback device Expired - Fee Related JP3785718B2 (en)

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JP4887060B2 (en) * 2006-03-07 2012-02-29 シャープ株式会社 Noise canceling headphones
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JP2509609Y2 (en) * 1984-08-10 1996-09-04 アイワ株式会社 Acoustic negative feedback device
JP2571091B2 (en) * 1988-03-18 1997-01-16 ティーオーエー株式会社 Speaker frequency response correction device
JPH0457994U (en) * 1990-09-26 1992-05-19
JP3097340B2 (en) * 1992-08-19 2000-10-10 ソニー株式会社 Headphone equipment
JP3147662B2 (en) * 1993-12-09 2001-03-19 松下電器産業株式会社 Sound reproduction device
JPH07162987A (en) * 1993-12-10 1995-06-23 Pioneer Electron Corp Noise reduction device
JP3552310B2 (en) * 1994-11-22 2004-08-11 松下電器産業株式会社 Speaker device and video equipment using the same
JP3344147B2 (en) * 1995-02-24 2002-11-11 ソニー株式会社 Speaker system
US5708722A (en) * 1996-01-16 1998-01-13 Lucent Technologies Inc. Microphone expansion for background noise reduction

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