JP2004173053A

JP2004173053A - Super-directional microphone device

Info

Publication number: JP2004173053A
Application number: JP2002337933A
Authority: JP
Inventors: Osamu Kasuya; 修粕谷
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2002-11-21
Filing date: 2002-11-21
Publication date: 2004-06-17

Abstract

<P>PROBLEM TO BE SOLVED: To provide a super-directional microphone device for collecting the natural sounds of a high sound quality, which is small-sized and has sharp directivity over all the bands. <P>SOLUTION: The super-directional microphone device has three unidirectional microphone cells (10, 11, and 12) arranged in the longitudinal direction with prescribed spacing and calculates a difference signal extracted from the output signals of the two microphone cells (10 and 12), the difference signal extracted from the output signals of the two microphone cells (11 and 12), and the difference signal between both difference signals and takes out a frequency signal higher than a prescribed frequency with a high-pass filter 16. A frequency signal lower than the frequency is taken out from the difference signal extracted from the output signals of the two microphone cells (10 and 12) with a low-pass filter 18. Phases in the vicinities of the band boundaries of the output signals of the filters (16 and 18) are matched, and corrected output signals are obtained with an equalizer circuit 20. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、音源に対する指向性の向上を図った超指向性マイクロフォン装置に関し、具体的には、小型で、全帯域に渡ってより鋭い指向性を有し、音質を重視した自然な音を収音するビデオカメラ等に使われて好適である。
【０００２】
【従来の技術】
従来より、超指向性マイクロフォン装置として、図５に示すような構造のものが広く知られている。特性の揃った二つの単一指向性マイクロフォン（１次音圧傾度型マイクロフォン）１および２を前後方向に所定の間隔を隔てて配置し、マイクロフォン１の出力信号を反転回路３で反転させた反転信号と、マイクロフォン２の出力信号をミックス回路４でミックス処理することによって両信号の差分信号を抽出する。
【０００３】
この差分信号は、横方向から入射する音に関しては同位相・同振幅信号の差成分となるため理論的にはゼロとなり、前方向から入射する音に関しては前方に配置されたマイクロフォン１と後方に配置されたマイクロフォン２の間隔を伝播する時間差分の位相差に応じた差成分が得られる（マイクロフォン間隔が音の波長の１／２に相当する時に最大出力が得られる）。
【０００４】
尚、後方向から入射する音に関しては単一指向性マイクロフォンの指向特性上からそれぞれのマイクロフォン出力の信号成分がゼロであるためその差成分もゼロである。イコライザ５は、差分信号の周波数特性をフラットに補正するのが目的の回路である。
従って、マイクロフォン１と２の差分信号を周波数補正したマイクロフォン出力は前方向に鋭い指向性を有するマイクロフォン装置（２次音圧傾度型マイクロフォン）として機能する。
【０００５】
また、特許文献１の技術は、音源に対して集音面を同一方向に向け、且つ指向性の主軸と直交する方向に所定の距離を隔てて配された、少なくとも３個の単一指向性マイクロフォン素子と、各マイクロフォン素子からの出力信号を加算する加算器とを備え、鋭い指向性を得るマイクロフォン装置を提案している。
【０００６】
【特許文献１】
国際公開第９６／２５０１８号パンフレット
【０００７】
【発明が解決しようとする課題】
上述の従来の技術を用いた２次音圧傾度型マイクロフォンは、周囲の雑音をカットして正面の目的音を収音し易くするため、望遠マイクロフォンとしての効果を得ることができる。
この２次音圧傾度型マイクロフォンと一般的なステレオマイクロフォン（またはモノラルマイクロフォン）を組み合わせ、両信号のミックス比を連続的に可変させればズームマイクロフォンとして機能することは一般に知られている。
これは、例えば民生用ビデオカメラのズームレンズと連動させることによって映像と音声が一緒にズームしているような効果を得ることができ、このような処理を行なった２次音圧傾度型マイクロフォンには、原理的に下記の課題が発生する。
【０００８】
（１）高域の帯域が狭くなる。
（２）低域感度が不足する。
（３）低域信号のＳ／Ｎが悪い。
【０００９】
原理的に、前後に配置するマイクロフォンの間隔によって確保し得る高域の帯域が制限される（確保できる高域の帯域は、マイクロフォン間隔が通過する音の波長の１／２に相当する周波数までである）。間隔を狭めれば高域の帯域は拡がるが、逆に低域感度が確保できなくなる。低域感度を確保するためにマイクロフォン間隔を広げると高域の帯域がますます狭くなる。
【００１０】
現実的には、この処理を行なった２次音圧傾度型マイクロフォンは、その鋭い指向性と引き換えに、確保できる周波数帯域が高域・低域共に不足したものとなり、音質的には満足いくものとはなり難い。
特に、前記のようなズームマイクロフォンとして機能させる場合、組合せるステレオマイクロフォン（またはモノラルマイクロフォン）側の周波数帯域はかなり広く確保できているために、特性をステレオマイクロフォン側（ワイド側）から２次音圧傾度型マイクロフォン側（テレ側）に変化させた時の音質差が際立ち、大きな違和感を与えるという問題がある。
【００１１】
また、より強いズーム感を得るためには、テレ側の特性を受け持っている超指向性マイクロフォン装置の指向性を更に鋭くする必要があるが、そのために音圧傾度の次数を更に上げるような処理を行なうと低域感度が益々不足し実用になり難いという課題がある。
【００１２】
また、特許文献１のマイクロフォン装置は、その主目的を音声認識装置の音声入力手段に置いているため、中音域でのみ鋭い指向性が得られるものである。対象方向からの人間の声のみを効率的に取り込む目的にはよいが、低域から高域までのすべての帯域の音を収音目的とするような一般的な用途には、周辺雑音の中音域成分のみがカットされた極めて不自然な音となり不向きである。
【００１３】
本発明は、上述の実情を考慮してなされたものであって、単一指向性マイクロフォンセルの前後方向配置を３個に増やし、中高域の指向性を更にアップさせると同時に低域の感度も改善する、または中低域のＳ／Ｎを同等に確保した上で高域の帯域を広げることができる、音質を重視した自然な音の収音用に、小型で、全帯域に渡ってより指向性の鋭い超指向性マイクロフォン装置を提供することを目的とする。
【００１４】
【課題を解決するための手段】
上記の課題を解決するために、本発明の請求項１の超指向性マイクロフォン装置は、３個の単一指向性マイクロフォンセルを前後方向に所定の間隔を隔てて配置（配置順に、第１マイクロフォンセル、第２マイクロフォンセル、第３マイクロフォンセルとする）し、第１マイクロフォンセルと第２マイクロフォンセルの出力信号から抽出した差分信号と、第２マイクロフォンセルと第３マイクロフォンセルの出力信号から抽出した差分信号とから、これらの両差分信号間の差分信号を抽出して、所定の周波数より高い周波数信号を第１フィルタ（ＨＰＦ：高域通過フィルタ）で取り出す。
また、第１マイクロフォンセルと第３マイクロフォンセルの出力信号から抽出した差分信号から、所定の周波数より低い周波数信号を第２フィルタ（ＬＰＦ：低域通過フィルタ）で取り出す。
これらの第１フィルタと第２フィルタの出力信号の帯域境界付近の位相を合わせて、その合成出力信号の周波数特性をイコライザ回路でフラット化して、鋭い指向性を実現する出力信号を得る。
【００１５】
以上の構成により、高域側の指向特性を更に鋭くしつつ低域感度を改善したり、中低域感度を劣化させること無く高域側帯域を広げる（しかも広げた帯域の指向性は非常に鋭いものとなる）ことが可能となる。
【００１６】
【発明の実施の形態】
以下、図面を参照して本発明に係る超指向性マイクロフォン装置の好適な実施形態について説明する。
図１は、本発明に係る超指向性マイクロフォン装置の実施形態の構成を示すブロック図であり、図１（Ａ）は３個の単一指向性マイクロフォンセルの配置を示し、図１（Ｂ）は全体の構成を示している。
図１（Ａ）に示すように、本実施形態では、特性の揃った３個の単一指向性マイクロフォンセル（第１マイクロフォンセル１０、第２マイクロフォンセル１１、第３マイクロフォンセル１２）が前後方向に等間隔で指向性の主軸が同一方向を向くように直列に配置されている。
【００１７】
図１（Ｂ）に示すように、本実施形態は、第１マイクロフォンセル１０と第２マイクロフォンセル１１の出力信号の差分信号を抽出する第１差分回路１３、第２マイクロフォンセル１１と第３マイクロフォンセル１２の出力信号の差分信号を抽出する第２差分回路１４、第１差分回路１３と第２差分回路１４の出力信号同士の差分信号を抽出する第３差分回路１５、第３差分回路１５の出力信号から所定の周波数より高い周波数帯域信号を抽出する第１フィルタ（ＨＰＦ：高域通過フィルタ）１６、第１マイクロフォンセル１０と第３マイクロフォンセル１２の出力信号の差分信号を抽出する第４差分回路１７、第４差分回路１７の出力信号から所定の周波数より低い周波数帯域信号を抽出する第２フィルタ（ＬＰＦ：低域通過フィルタ）１８、第２フィルタ１８からの出力信号の位相を第１フィルタ１６からの出力信号の位相に合わせた信号と第１フィルタ１６の出力信号を加算する加算回路１９、加算回路１９の出力信号の周波数特性を補正するイコライザ回路（ＥＱ）２０とから構成される。
【００１８】
上記のように構成した超指向性マイクロフォン装置では、まず、同じ間隔ｄを隔てて前後方向に配置された第１マイクロフォンセル１０と第２マイクロフォンセル１１間、および第２マイクロフォンセル１１と第３マイクロフォンセル１２間で従来行なわれてきた２次音圧傾度型マイクロフォン処理（差分信号抽出処理）を行なう。
本実施形態では、図１（Ｃ）に示すように、各差分回路（１３，１４，１５，１７）は、前方に配置されている側のマイクロフォンセルの出力信号（信号ａ）に位相を反転させる位相反転回路３１を入れ、後方に配置されている側のマイクロフォンセルの出力信号（信号ｂ）とミックス処理するミックス回路３２を入れて差分信号ｃ（２次音圧傾度型信号）を抽出する。
【００１９】
更に、それぞれ第１差分回路１３と第２差分回路１４で抽出された差分信号（２次音圧傾度型信号）同士の差分信号を第３差分回路１５で抽出する。この第３差分回路１５からの出力信号は、４次音圧傾度相当の鋭い指向性を有する信号（Ｓ１）となり、従来の２次音圧傾度型よりも更に鋭い指向性を実現できる（図２参照）。
【００２０】
しかし、イコライザ処理を加える前の２次音圧傾度型の周波数特性が最大出力周波数ｆに向かって６ｄＢ／ｏｃｔの傾斜であるのに対し、上述の処理を加えた４次音圧傾度相当の周波数特性は最大出力周波数ｆに向かって１２ｄＢ／ｏｃｔの傾斜になるため低域の感度は非常に低くなってしまい、そのままでの実用は難しい。そこで、低域感度を次のようにして確保する。
【００２１】
本実施形態において、第１マイクロフォンセル１０と第３マイクロフォンセル１２の間隔が２ｄであるから、第１マイクロフォンセル１０と第３マイクロフォンセル１２間の差分信号を第４差分回路１７で抽出することによって、最大出力周波数をｆ／２とした２次音圧傾度型の出力信号（Ｓ２）を得ることができる。
この出力信号は、ｆ／２以下の周波数帯域では、マイクロフォンセル間隔がｄの時の２次音圧傾度型信号に比べて６ｄＢ高い感度を有する。
【００２２】
更に、ｆ／２より低い所定の周波数ｆ０をカットオフ周波数とする第１フィルタ１６（ＨＰＦ：高域通過フィルタ）に４次音圧傾度相当信号（Ｓ１）を通し、同じくｆ０をカットオフ周波数とする第２フィルタ１８（ＬＰＦ：低域通過フィルタ）に２次音圧傾度型信号（Ｓ２）を通して、加算回路１９でミックス処理することによって、ｆ０より高い周波数帯域では４次音圧傾度相当の非常に高い指向性を備え、且つ、ｆ０より低い周波数帯域では２次音圧傾度相当の指向性ながら低域感度が高い出力信号を得ることができる。
【００２３】
この加算回路１９は、図１（Ｄ）に示すように、第２フィルタ１８からの出力信号（信号ｅ）の位相を第１フィルタ１６の出力信号（信号ｆ）の位相に合わせた信号を出力する移相回路４１、移相回路４１からの出力信号と信号ｆとをミックスした信号ｇを出力するミックス回路４２から構成される。
【００２４】
最終的に、加算回路１９からの出力信号をイコライザ回路２０にて周波数特性全体のフラット化が行なわれ、中高域指向性に優れ、中低域Ｓ／Ｎの良好な出力信号を実現できる。
【００２５】
また、本実施形態のマイクロフォンセルの間隔をｄ／２に設定した場合、マイクロフォンセルの間隔が１／２になることによって、４次音圧傾度相当信号（Ｓ１）の高域側の帯域は２倍となるが、帯域が伸びた分、低域感度は益々低くなるが、２次音圧傾度型の出力信号（Ｓ２）としては、マイクロフォンセル間隔ｄの現状２次音圧傾度型の出力信号そのままを得る。
【００２６】
従って、本実施形態の出力信号は、現状同等の中低域特性を保持した上で、高域は４次音圧傾度相当の鋭い指向性を実現し、且つ帯域を２倍に拡大した出力信号を得ることが可能となる。
【００２７】
＜実施例１＞
まず、実施例１としてマイクロフォンセルの間隔ｄを３４ｍｍに設定した場合について説明する。
一対のマイクロフォンセル間で差分信号抽出処理を行なった後の正面方向入力音信号の周波数特性は、次の式１で表すことができる。
【００２８】
Ｅｏ＝Ｅ√｛（１−ｃｏｓα）^２＋ｓｉｎ^２α｝ … 式１
ここで α＝（２πｆｄ）／ｃ
ｃ≒３４０［ｍ／ｓ］：（音速）
ｆ：周波数［Ｈｚ］
ｄ：マイクロフォンセル間隔［ｍ］
Ｅ：マイクロフォン出力レベル
Ｅｏ：差分信号レベル
【００２９】
この式１に、ｄ＝３４ｍｍを適用すると、差分信号の周波数特性は図３の曲線ａになる。この差分信号同士で更に差分信号を取った４次音圧傾度相当信号（Ｓ１）の周波数特性は、図３の曲線ｂとなる。
また、マイクロフォンセル間隔が２ｄ＝６８ｍｍとなる第１マイクロフォンセル１０と第３マイクロフォンセル１２間の差分信号（Ｓ２）の周波数特性は、図３の曲線ｃとなる。
図３の曲線ａと曲線ｂの最大出力が得られる周波数は、５ｋＨｚであり、１．６５ｋＨｚより高い周波数帯域においては、曲線ｂの方が高い感度を得ることができることを示している。
【００３０】
一方、図３の曲線ｃの最大出力が得られる周波数は、２．５ｋＨｚであるが、それより低い周波数帯域では常に曲線ａより６ｄＢ高い感度が得られることを示している。
【００３１】
従って、本実施例１で第１フィルタ１６と第２フィルタ１８のカットオフ周波数ｆ０を１．６５ｋＨｚ付近に設定すれば、全帯域に渡って従来技術による周波数特性ａよりも高い感度が確保できることになる。
また、ｆ０よりも高い周波数帯域においては、従来技術によるよりも更に鋭い指向特性が得られる。
【００３２】
＜実施例２＞
次に、実施例２としてマイクロフォンセル間隔ｄを１７ｍｍに設定した場合について説明する。
上述の式１にｄ＝１７ｍｍを適用すると、差分信号の周波数特性は図４の曲線ａとなり、この差分信号同士で更に差分信号を取った４次音圧傾度相当信号（Ｓ１）の周波数特性は、図４の曲線ｂとなる。
また、マイクロフォンセル間隔が２ｄ＝３４ｍｍとなる第１マイクロフォンセル１０と第３マイクロフォンセル１２間の差分信号（Ｓ２）の周波数特性は図４の曲線ｃとなる。
【００３３】
図４の曲線ａと曲線ｂの最大出力が得られる周波数は１０ｋＨｚであり、３．３５ｋＨｚより高い周波数帯域においては曲線ｂの方が高い感度を得ることができることを示している。
一方、図４の曲線ｃの最大出力が得られる周波数は５ｋＨｚであり、これは従来技術による２次音圧傾度型の特性そのものである。
【００３４】
従って、本実施例２の第１フィルタ１６と第２フィルタ１８のカットオフ周波数ｆ０を５ｋＨｚ付近に設定すれば、５ｋＨｚ以下の帯域で従来特性を維持したままで高域側帯域を１０ｋＨｚまで伸ばすことが可能となる。
また、伸びた高域側の指向性は４次音圧傾度相当の非常に鋭いものとなる。
【００３５】
【発明の効果】
以上説明したように本発明によると、高域側の指向特性を更に鋭くしつつ低域感度を改善したり、中低域感度を劣化させること無く高域側帯域を広げる（しかも広げた帯域の指向性は非常に鋭いものとなる）ことが可能となる。
【図面の簡単な説明】
【図１】本発明に係る超指向性マイクロフォン装置の実施形態の構成を示すブロック図であり、（Ａ）は３個の単一指向性マイクロフォンセルの配置を示し、（Ｂ）は全体の構成を示すブロック図である。
【図２】本発明の実施形態を説明する指向特性図である。
【図３】実施例１を説明する周波数特性図である。
【図４】実施例２を説明する周波数特性図である。
【図５】従来の指向性マイクロフォン装置の構成を示すブロック図である。
【符号の説明】
１，２…マイクロフォン、３…反転回路、４…ミックス回路、５…イコライザ、１０…第１マイクロフォンセル、１１…第２マイクロフォンセル、１２…第３マイクロフォンセル、１３…第１差分回路、１４…第２差分回路、１５…第３差分回路、１６…第１フィルタ（ＨＰＦ：高域通過フィルタ）、１７…第４差分回路、１８…第２フィルタ（ＬＰＦ：低域通過フィルタ）、１９…加算回路、２０…イコライザ回路、３１…位相反転回路、３２，４２…ミックス回路、４１…移相回路。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a super-directional microphone device that improves directivity with respect to a sound source, and specifically, is small in size, has sharp directivity over the entire band, and collects natural sound with emphasis on sound quality. It is suitable for use in video cameras that make sound.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a superdirective microphone device having a structure as shown in FIG. 5 has been widely known. Two unidirectional microphones (primary sound pressure gradient type microphones) 1 and 2 having uniform characteristics are arranged at a predetermined interval in the front-rear direction, and the output signal of the microphone 1 is inverted by an inversion circuit 3. The signal and the output signal of the microphone 2 are mixed by a mixing circuit 4 to extract a difference signal between the two signals.
[0003]
This difference signal is theoretically zero for a sound incident from the lateral direction because it is a difference component between the same phase and the same amplitude signal. For a sound incident from the front direction, the microphone 1 arranged in front and the microphone 1 arranged rearward A difference component corresponding to the phase difference of the time difference propagating in the interval between the arranged microphones 2 is obtained (the maximum output is obtained when the microphone interval corresponds to half the wavelength of the sound).
[0004]
In addition, regarding the sound incident from the rear direction, the signal component of each microphone output is zero because of the directivity characteristics of the unidirectional microphone, so that the difference component thereof is also zero. The equalizer 5 is a circuit whose purpose is to correct the frequency characteristics of the difference signal flat.
Accordingly, the microphone output obtained by frequency-correcting the difference signal between the microphones 1 and 2 functions as a microphone device (secondary sound pressure gradient type microphone) having sharp directivity in the forward direction.
[0005]
In addition, the technique disclosed in Patent Document 1 discloses that at least three unidirectional light sources are arranged at a predetermined distance in a direction orthogonal to a main axis of directivity, with a sound collection surface oriented in the same direction with respect to a sound source. A microphone device that includes a microphone element and an adder that adds output signals from the microphone elements and obtains sharp directivity has been proposed.
[0006]
[Patent Document 1]
WO 96/25018 pamphlet [0007]
[Problems to be solved by the invention]
The secondary sound pressure gradient type microphone using the above-described conventional technology can obtain the effect as a telephoto microphone because the surrounding noise is cut to easily collect the target sound in front.
It is generally known that the secondary sound pressure gradient type microphone is combined with a general stereo microphone (or monaural microphone) and functions as a zoom microphone if the mix ratio of both signals is continuously varied.
For example, it is possible to obtain an effect that video and audio are zoomed together by linking with a zoom lens of a consumer video camera, and a secondary sound pressure gradient type microphone that performs such processing can be obtained. In principle, the following problems occur.
[0008]
(1) The high frequency band becomes narrow.
(2) Low sensitivity is insufficient.
(3) The S / N of the low-frequency signal is poor.
[0009]
In principle, the high-frequency band that can be secured is limited by the spacing between the microphones arranged before and after (the high-frequency bandwidth that can be secured is up to a frequency corresponding to half the wavelength of the sound passing through the microphone spacing). is there). If the interval is narrowed, the high frequency band is widened, but low frequency sensitivity cannot be ensured. Increasing the microphone spacing to ensure low-frequency sensitivity will further narrow the high-frequency band.
[0010]
Realistically, the secondary sound pressure gradient type microphone that has performed this processing has insufficient frequency bands for both high and low frequencies in exchange for its sharp directivity, and is satisfactory in sound quality. It is hard to be.
In particular, when functioning as a zoom microphone as described above, since the frequency band on the side of the stereo microphone (or monaural microphone) to be combined can be assured considerably wide, the characteristic is changed from the stereo microphone side (wide side) to the secondary sound pressure. There is a problem that a difference in sound quality when changing to the gradient microphone side (tele side) stands out, giving a great sense of discomfort.
[0011]
Also, in order to obtain a stronger zoom feeling, it is necessary to further sharpen the directivity of the super-directional microphone device that is responsible for the characteristics on the telephoto side. In this case, there is a problem that the low-frequency sensitivity is increasingly insufficient and it is difficult to be practical.
[0012]
Further, the microphone device disclosed in Patent Literature 1 has its main purpose in the voice input means of the voice recognition device, and thus can obtain sharp directivity only in the middle sound range. It is good for efficiently capturing only human voices from the target direction, but for general use where sound in all bands from low to high is to be collected, there is no This is an extremely unnatural sound with only the treble component cut off, and is not suitable.
[0013]
The present invention has been made in consideration of the above-described circumstances, and the number of unidirectional microphone cells has been increased to three in the front-rear direction, thereby further improving the directivity in the middle and high ranges and simultaneously improving the sensitivity in the low range. Improves or expands the high frequency band while securing the S / N of the middle and low frequency range. It is an object of the present invention to provide a super-directional microphone device having sharp directivity.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a super directional microphone device according to claim 1 of the present invention arranges three unidirectional microphone cells at predetermined intervals in the front-rear direction (in the arrangement order, the first microphone). Cell, a second microphone cell, and a third microphone cell), a differential signal extracted from the output signals of the first and second microphone cells, and an output signal of the second and third microphone cells. A difference signal between these two difference signals is extracted from the difference signal, and a frequency signal higher than a predetermined frequency is extracted by a first filter (HPF: high-pass filter).
Further, a frequency signal lower than a predetermined frequency is extracted by a second filter (LPF: low-pass filter) from a difference signal extracted from output signals of the first microphone cell and the third microphone cell.
The output signals of the first filter and the second filter are matched in phase near the band boundary, and the frequency characteristics of the combined output signal are flattened by an equalizer circuit to obtain an output signal realizing sharp directivity.
[0015]
With the above configuration, the low-pass sensitivity is improved while sharpening the directional characteristics on the high-pass side, and the high-pass band is expanded without deteriorating the mid-low-pass sensitivity (and the directivity of the widened band is very high). Sharp).
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of a super-directional microphone device according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an embodiment of a super-directional microphone device according to the present invention. FIG. 1A shows an arrangement of three unidirectional microphone cells, and FIG. Indicates the entire configuration.
As shown in FIG. 1A, in the present embodiment, three unidirectional microphone cells (first microphone cell 10, second microphone cell 11, and third microphone cell 12) having uniform characteristics are arranged in the front-rear direction. Are arranged in series at equal intervals so that the main axes of directivity face the same direction.
[0017]
As shown in FIG. 1B, in the present embodiment, a first difference circuit 13 that extracts a difference signal between output signals of a first microphone cell 10 and a second microphone cell 11, a second microphone cell 11, and a third microphone A second difference circuit 14 for extracting a difference signal of the output signal of the cell 12, a third difference circuit 15 for extracting a difference signal between the output signals of the first difference circuit 13 and the second difference circuit 14, and a third difference circuit 15 A first filter (HPF: high-pass filter) 16 for extracting a frequency band signal higher than a predetermined frequency from the output signal, and a fourth difference for extracting a difference signal between the output signals of the first microphone cell 10 and the third microphone cell 12 A second filter (LPF: low-pass filter) 1 for extracting a frequency band signal lower than a predetermined frequency from an output signal of the circuit 17 and the fourth difference circuit 17 An addition circuit 19 for adding a signal obtained by matching the phase of the output signal from the second filter 18 with the phase of the output signal from the first filter 16 and the output signal of the first filter 16, and the frequency characteristic of the output signal of the addition circuit 19 And an equalizer circuit (EQ) 20 that corrects
[0018]
In the super-directional microphone device configured as described above, first, between the first microphone cell 10 and the second microphone cell 11 and the second microphone cell 11 and the third microphone arranged in the front-rear direction at the same interval d. The secondary sound pressure gradient type microphone processing (difference signal extraction processing) conventionally performed between the cells 12 is performed.
In the present embodiment, as shown in FIG. 1C, each of the difference circuits (13, 14, 15, 17) inverts the phase of the output signal (signal a) of the microphone cell disposed on the front side. A phase inverting circuit 31 is provided, and an output signal (signal b) of the microphone cell disposed on the rear side is provided with a mix circuit 32 for performing mixing processing, thereby extracting a difference signal c (secondary sound pressure gradient type signal). .
[0019]
Further, a third difference circuit 15 extracts a difference signal between the difference signals (secondary sound pressure gradient type signals) extracted by the first difference circuit 13 and the second difference circuit 14, respectively. The output signal from the third difference circuit 15 is a signal (S1) having a sharp directivity equivalent to the fourth sound pressure gradient, and can realize a sharper directivity than the conventional secondary sound pressure gradient type (FIG. 2). reference).
[0020]
However, while the frequency characteristic of the secondary sound pressure gradient type before the equalizer processing is applied has a slope of 6 dB / oct toward the maximum output frequency f, the frequency corresponding to the fourth sound pressure gradient subjected to the above processing is applied. Since the characteristics have a slope of 12 dB / oct toward the maximum output frequency f, the sensitivity in the low frequency range is extremely low, and practical use as it is is difficult. Therefore, low-frequency sensitivity is ensured as follows.
[0021]
In the present embodiment, since the distance between the first microphone cell 10 and the third microphone cell 12 is 2d, the difference signal between the first microphone cell 10 and the third microphone cell 12 is extracted by the fourth difference circuit 17. Thus, a secondary sound pressure gradient type output signal (S2) having a maximum output frequency of f / 2 can be obtained.
This output signal has a sensitivity 6 dB higher in the frequency band of f / 2 or less than the secondary sound pressure gradient signal when the microphone cell interval is d.
[0022]
Further, a fourth-order sound pressure gradient equivalent signal (S1) is passed through a first filter 16 (HPF: high-pass filter) having a predetermined frequency f0 lower than f / 2 as a cutoff frequency, and f0 is also set as a cutoff frequency. The second sound pressure gradient type signal (S2) is passed through a second filter 18 (LPF: low-pass filter) to be mixed by an adder circuit 19, so that in a frequency band higher than f0, an extremely high frequency sound pressure gradient corresponding to the fourth sound pressure gradient is obtained. In a frequency band lower than f0, it is possible to obtain an output signal with high low-frequency sensitivity while having directivity corresponding to the secondary sound pressure gradient.
[0023]
The adder circuit 19 outputs a signal in which the phase of the output signal (signal e) from the second filter 18 matches the phase of the output signal (signal f) of the first filter 16 as shown in FIG. And a mix circuit 42 that outputs a signal g obtained by mixing the output signal from the phase shift circuit 41 and the signal f.
[0024]
Finally, the output signal from the adder circuit 19 is flattened in the entire frequency characteristics by the equalizer circuit 20, so that an output signal that is excellent in directivity in the middle and high ranges and has a good S / N in the middle and low ranges can be realized.
[0025]
Further, when the interval between the microphone cells of the present embodiment is set to d / 2, the interval between the microphone cells becomes によって, so that the band on the high frequency side of the fourth-order sound pressure gradient equivalent signal (S1) becomes 2 Although the low frequency sensitivity becomes lower as much as the band is extended, the secondary sound pressure gradient type output signal (S2) is the current secondary sound pressure gradient type output signal with the microphone cell interval d. Get it as is.
[0026]
Therefore, the output signal of this embodiment realizes a sharp directivity equivalent to the fourth-order sound pressure gradient in the high frequency range while maintaining the same mid-low frequency characteristics as it is currently, and an output signal in which the band is doubled. Can be obtained.
[0027]
<Example 1>
First, a case where the distance d between the microphone cells is set to 34 mm will be described as a first embodiment.
The frequency characteristic of the front-direction input sound signal after performing the difference signal extraction processing between the pair of microphone cells can be expressed by the following equation 1.
[0028]
Eo = E {(1−cos α) ² + sin ² α} Equation 1
Where α = (2πfd) / c
c ≒ 340 [m / s]: (Sound speed)
f: Frequency [Hz]
d: Microphone cell interval [m]
E: microphone output level Eo: differential signal level
When d = 34 mm is applied to the equation 1, the frequency characteristic of the difference signal becomes a curve a in FIG. The frequency characteristic of the fourth-order sound pressure gradient equivalent signal (S1) obtained by further taking a difference signal between the difference signals is a curve b in FIG.
Further, the frequency characteristic of the difference signal (S2) between the first microphone cell 10 and the third microphone cell 12 in which the microphone cell interval is 2d = 68 mm is a curve c in FIG.
The frequency at which the maximum output of the curves a and b in FIG. 3 is obtained is 5 kHz, and shows that the curve b can obtain higher sensitivity in a frequency band higher than 1.65 kHz.
[0030]
On the other hand, the frequency at which the maximum output of the curve c in FIG. 3 is obtained is 2.5 kHz, but shows that sensitivity 6 dB higher than that of the curve a is always obtained in a lower frequency band.
[0031]
Therefore, in the first embodiment, if the cutoff frequency f0 of the first filter 16 and the second filter 18 is set to around 1.65 kHz, a higher sensitivity than the frequency characteristic a according to the related art can be secured over the entire band. Become.
Further, in a frequency band higher than f0, a sharper directional characteristic can be obtained as compared with the related art.
[0032]
<Example 2>
Next, a case where the microphone cell interval d is set to 17 mm will be described as a second embodiment.
When d = 17 mm is applied to the above equation 1, the frequency characteristic of the differential signal becomes curve a in FIG. 4, and the frequency characteristic of the fourth-order sound pressure gradient equivalent signal (S1) obtained by further taking the differential signal between the differential signals is 4 becomes the curve b in FIG.
In addition, the frequency characteristic of the difference signal (S2) between the first microphone cell 10 and the third microphone cell 12 where the microphone cell interval is 2d = 34 mm is a curve c in FIG.
[0033]
The frequency at which the maximum output of the curves a and b in FIG. 4 is obtained is 10 kHz, and the curve b shows that higher sensitivity can be obtained in a frequency band higher than 3.35 kHz.
On the other hand, the frequency at which the maximum output of the curve c in FIG. 4 is obtained is 5 kHz, which is the characteristic itself of the secondary sound pressure gradient type according to the prior art.
[0034]
Therefore, if the cutoff frequency f0 of the first filter 16 and the second filter 18 of the second embodiment is set to around 5 kHz, the high-frequency band can be extended to 10 kHz while maintaining the conventional characteristics in the band of 5 kHz or less. Becomes possible.
Also, the extended directivity on the high frequency side becomes very sharp, equivalent to the fourth sound pressure gradient.
[0035]
【The invention's effect】
As described above, according to the present invention, the low-pass sensitivity is improved while sharpening the directional characteristics on the high-pass side, or the high-pass band is expanded without deteriorating the middle-low-pass sensitivity (and the expanded The directivity can be very sharp).
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a super-directional microphone device according to the present invention, wherein (A) shows an arrangement of three unidirectional microphone cells, and (B) shows an overall configuration. FIG.
FIG. 2 is a directional characteristic diagram illustrating an embodiment of the present invention.
FIG. 3 is a frequency characteristic diagram for explaining the first embodiment;
FIG. 4 is a frequency characteristic diagram illustrating the second embodiment.
FIG. 5 is a block diagram showing a configuration of a conventional directional microphone device.
[Explanation of symbols]
1, 2,... Microphone 3, inverting circuit 4, mixing circuit 5, equalizer 10, first microphone cell 11, second microphone cell 12, third microphone cell 13, first difference circuit 14, Second difference circuit, 15: third difference circuit, 16: first filter (HPF: high-pass filter), 17: fourth difference circuit, 18: second filter (LPF: low-pass filter), 19: addition Circuit, 20: equalizer circuit, 31: phase inversion circuit, 32, 42: mix circuit, 41: phase shift circuit.

Claims

In a microphone device having unidirectional microphone cells arranged therein and having directivity in the forward direction, three unidirectional microphone cells are arranged at predetermined intervals in the front-rear direction (hereinafter, the first microphone is arranged in the order of arrangement). Cell, a second microphone cell, and a third microphone cell), a first difference circuit for extracting a difference signal between the output signals of the first microphone cell and the second microphone cell, the second microphone cell and the third microphone cell. A second differential circuit for extracting a differential signal of the output signal of the microphone cell; a third differential circuit for extracting a differential signal between the output signals of the first differential circuit and the second differential circuit; A first filter for extracting a frequency band signal higher than a predetermined frequency from an output signal; the first microphone cell and the third filter; A fourth difference circuit for extracting a difference signal of the output signal of the crophone cell, a second filter for extracting a frequency band signal lower than a predetermined frequency from the output signal of the fourth difference circuit, and an output signal of the first filter A super-directional microphone, comprising: an adder circuit for performing a mixing process by adjusting a phase near a band boundary of an output signal of the second filter, and an equalizer circuit for correcting a frequency characteristic of an output signal of the adder circuit. apparatus.

2. The super-directional microphone device according to claim 1, wherein each of the difference circuits includes a phase inversion circuit for inverting a phase of an output signal of a microphone cell on a front side and a phase inversion circuit on a rear side. A super directional microphone device comprising a mix circuit that mixes an output signal of a microphone cell and an output signal from the phase inversion circuit.

2. The superdirective microphone device according to claim 1, wherein the adding circuit outputs a signal in which a phase of an output signal from the second filter matches a phase of an output signal of the first filter, and A super directional microphone device comprising: a mix circuit that mixes an output signal from the phase shift circuit and an output signal from the first filter.

Three unidirectional microphone cells are arranged at predetermined intervals in the front-rear direction, two secondary sound pressure gradient signals of adjacent microphone cells are obtained, and 4 secondary sound pressure gradient signals are obtained from these secondary sound pressure gradient signals. The signal corresponding to the next sound pressure gradient is passed through a high-pass filter, the secondary sound pressure gradient signals of the first microphone cell and the last microphone cell are obtained and passed through a low-pass filter, and the output signals of these two filters are output. A super directional microphone device that performs an equalizer process for correcting a frequency characteristic by performing a mixing process by adjusting a phase near a band boundary.