JP2004354769A

JP2004354769A - Active silencer

Info

Publication number: JP2004354769A
Application number: JP2003153369A
Authority: JP
Inventors: Akihiko Ebato; 明彦江波戸; Hajime Kudo; 肇工藤; Yoshiyuki Sato; 義之佐藤
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2003-05-29
Filing date: 2003-05-29
Publication date: 2004-12-16
Anticipated expiration: 2023-05-29
Also published as: JP4110043B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active silencer capable of deadening entire area noise of a three-dimensional space at a real time even to a face sound source of an amplitude and phase characteristics indicating non-correlation distribution without measuring sound pressure and the phase of a noise source E and without using an error microphone. <P>SOLUTION: The active silencer comprises a ventilation duct 30 arranged to oppose the inlet to the noise source E, a sound pressure detection microphone 40 arranged in the inside of the ventilation duct 30, n-pieces of speaker 50 arranged at an outlet side of the ventilation duct 30, a fixing coefficient calculator determined by a distance between the speakers, a fluctuation coefficient calculator 101 for calculating a fluctuation coefficient on the basis of a distance between the ventilation duct 30 and the speaker 50 and the sound pressure from a sound pressure detection microphone 40, and an amplitude and phase calculator 103 for driving the speakers 50 so as to minimize acoustic power of radiation sound from the outlet of the ventilation duct 30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば、騒音源等の低減対象音発生源から発生した騒音を低減するための能動消音装置に関し、特に振幅・位相特性が無相関分布を呈する面音源や、開口部からの放射音に好適なものに関する。
【０００２】
【従来の技術】
振幅・位相特性が無相関分布を呈する面音源に対する３次元空間の能動消音方法として、複数のマイクとスピーカ（付加音源）を使い、局所的に消音するものは知られている。しかしながら、発生源から全域を消音するものは知られていない。なお、面音源がダクト開口部で観測できるケースにおいては、ダクト内部に仕切り板を挿入し、各仕切内部で音が平面波になるように仕切り間隔を調整することで音源分布を点音源群に変換することで、能動制御可能としたものがある。
【０００３】
【特許文献１】
特開２００２−３０３１１４号公報
【０００４】
【特許文献２】
特開平６−１５３９２０号公報
【０００５】
【発明が解決しようとする課題】
上述した能動消音方法であると次のような問題があった。すなわち、空間全域の消音を行うためには、各仕切部毎の音圧、位相計測が必要な上に、これに基づきエラーマイク（適応制御で用いる制御マイク）を用いて、このマイク位置の最適化を図る計算が必要となる。つまり、全域消音を導くための最適評価関数にあたる音響パワーはマイク位置（音圧最小点）の関数になるからである。
【０００６】
そこで本発明は、低減対象音源の音圧や位相計測をすることなく、かつ、エラーマイクを使用することなく、振幅・位相特性が無相関分布を呈する面音源に対してもリアルタイムで３次元空間の全域消音を行うことができる能動消音装置を提供することを目的としている。
【０００７】
【課題を解決するための手段】
上記課題を解決し目的を達成するために、本発明の能動消音装置は次のように構成されている。
【０００８】
（１）低減対象音源から発せられた低減対象音を低減する能動消音装置において、前記低減対象音源にその入口をそれぞれ対向させて配置された複数の通気ダクトと、前記通気ダクト内部にそれぞれ配置された音圧検出用マイクと、前記通気ダクト出口側に配置された複数の付加音源と、前記付加音源同士の距離で決まる固定係数算出部と、前記通気ダクトと前記付加音源との距離及び前記音圧検出用マイクからの音圧に基づいて変動係数を算出する変動係数算出部と、前記固定係数及び前記変動係数に基づいて、前記通気ダクト出口からの放射音の音響パワーを最小とするように前記付加音源を駆動する振幅・位相算出部とを備えていることを特徴とする。
【０００９】
（２）上記（１）に記載された能動消音装置であって、前記通気ダクト及び前記音圧検出用マイクの数をＭ、前記付加音源の数をＮ、ｉ番目とｊ番目の付加音源間の距離をｒ_ＳｉＳｊ、ｊ番目の騒音源とｉ番目の付加音源間の距離をｒ_ＰｊＳｉ、純虚数をｖ、角周波数をω、空気密度をρ、波数をｋ、ｉ番目の音圧検出用マイクからｉ番目の通気ダクト出口までの伝達関数をＣｉ、ｉ番目の付加音源の出力特性をＧｉ、マトリクスＡの要素をａ_ｉｊ、ベクトルｂの要素をｂ’_ｉ、前記音圧検出用マイク出力信号に伝達関数Ｃｉ／Ｇｉを乗じた信号をＸｊ、前記付加音源の最適振幅をｑ _{ｓ，ｏｐｔ}としたときに、
【数２】

を満たすものであることを特徴とする。
【００１０】
（３）上記（１）に記載された能動消音装置であって、前記付加音源の数は、前記通気ダクトの数と同じであり、前記付加音源は前記通気ダクトの出口外側に配置され、かつ、その音は通気ダクト外部に向けて放射するものであることを特徴とする。
【００１１】
【発明の実施の形態】
図１は本発明の一実施の形態に係る能動消音装置１０を示す図である。能動消音装置１０は、騒音源Ｅから発生した騒音に付加音を干渉させることで受音空間Ｌにおける音圧レベルを低減しようとするものである。能動消音装置１０は、騒音源Ｅ付近に設置された音響フィルタユニット２０と、この音響フィルタユニット２０の各部を制御する制御部１００とを備えている。なお、図中Ｅは騒音源（低減対象音源）、Ｐは仮想騒音源を示している。
【００１２】
音響フィルタユニット２０は、マトリクス状に配置されたＭ個の通気ダクト３０と、これら通気ダクト３０の内部であってそれぞれの騒音源Ｅ側に配置されたＭ個の音圧検出用マイク４０と、通気ダクト３０の受音空間Ｌ側に配置され付加音を発生するＮ個のスピーカ５０とを備えている。なお、Ｎは２以上Ｍ以下に設定されている。
【００１３】
通気ダクト３０は、その断面寸法（長辺）が騒音源Ｅからの騒音の半波長未満、また、その奥行き寸法（音の進行方向）が騒音の半波長以上となるように設定されている。なお、このように設定されていると、通気ダクト３０に入射した騒音は振幅・位相が無相関の放射特性をもった騒音源Ｅからの騒音は、通気ダクト３０内部で平面波伝播し、各通気ダクト３０の出口では点音源の放射として近似することが可能になる。また、音圧検出用マイク４０の出力後段には、後述するように時間ずれの補正を行うフィルタが設けられている。
【００１４】
制御部１００は、各通気ダクト３０と各スピーカ５０との距離及びＭ個の音圧検出用マイク４０からの各音圧レベルに基づいて変動係数を算出する変動係数算出部１０１と、Ｎ個のスピーカ５０同士の距離で決まる固定係数を記憶する固定係数記憶部１０２と、固定係数と変動係数とに基づいてスピーカ５０による付加音の振幅・位相を算出する振幅・位相算出部１０３とを備えている。振幅・位相算出部１０３では、変動係数算出部１０１の計算をリアルタイムで処理することにより各通気ダクト３０から放射した音の音響パワーを最小とするような演算が行われる。
【００１５】
このように構成された能動消音装置１０では、次のようにして消音が行われる。すなわち、騒音源Ｅからの騒音は音響フィルタユニット２０の各通気ダクト３０内に入る。各通気ダクト３０内に配置された音圧検出用マイク４０で検出された音圧信号は、変動係数算出部１０１に入力される。変動係数算出部１０１では、変動係数ｂが算出され、振幅・位相算出部１０３に入力される。一方、固定係数記憶部１０２から固定係数Ａが振幅・位相算出部１０３に入力される。
【００１６】
振幅・位相算出部１０３では、変動係数ｂ及び固定係数Ａに基づいて、各通気ダクト３０から放射する放射音を最小とするようなスピーカ５０からの付加音の振幅及び位相を算出し、算出結果に基づいて付加音を発生させる。
【００１７】
次に、能動消音装置１０における付加音の算出方法を説明する。ここで、ｉ番目とｊ番目のスピーカ５０間の距離をｒ_ＳｉＳｊ、ｊ番目の仮想騒音源Ｐとｉ番目のスピーカ５０間の距離をｒ_ＰｊＳｉ、純虚数をｖ、角周波数をω、空気密度をρ、波数をｋ、ｉ番目の音圧検出用マイク４０からｉ番目の通気ダクト３０出口までの伝達関数をＣｉ、ｉ番目の付加音源の出力特性をＧｉ、マトリクスＡの要素をａ_ｉｊ、ベクトルｂの要素をｂ’_ｉ、音圧検出用マイク４０の出力信号に伝達関数Ｃｉ／Ｇｉを乗じた信号をＸｊ、スピーカ５０の最適振幅をｑ _{ｓ，ｏｐｔ}とする。
【００１８】
付加音の振幅・位相は通気ダクト３０への入射の仕方や騒音源Ｅ自体の特性に影響され、必ずしもＭ個全て一致しているとは限らないものの、この音響フィルタユニット２０により、騒音源特性は複素振幅の異なるＭ個の仮想騒音源Ｐによる離散点音源群に変換される。
【００１９】
Ｍ個の仮想騒音源Ｐからの騒音とＮ個のスピーカ５０からの付加音からなる全音響パワーＰ_ｗｔを次のように示すことができる。なお、ｑ _Ｓはスピーカ５０の複素振幅（体積速度）ベクトル、ｑ _ｐは仮想騒音源Ｐの複素振幅（体積速度）ベクトル，ｂ，ｃも同様に複素ベクトル、Ａ，Ｄはマトリクスを示している。さらに、Ｒｅは複素実部、Ｈは共役転置を示している。
【００２０】

ｑ _Ｓ ^Ｔ＝（ｑ_Ｓ１ｑ_Ｓ２ … ｑ_Ｓｎ）〜（５）
ｂ ^Ｔ＝（ｂ_１ｂ_２ … ｂ_ｎ）〜（６）
ｃ ^Ｔ＝（ｃ_１ｃ_２ … ｃ_ｎ）〜（７）
なお、式（４）の第１項は付加音源だけ単独で鳴らしたときの音響パワー、第４項は騒音源だけ単独で鳴らしたときの音響パワー、第２項及び第３項は仮想騒音源Ｐと付加音源５０間の干渉により生ずる音響パワーに相当する。
【００２１】
また、マトリクスＡの要素ａ_ｉｊ、ベクトルｂ，ｃの要素ｂ_ｉ，ｃ_ｉ及びマトリクスＤの要素ｄ_ｉｊは次式のように記述できる。
【００２２】
【数３】

【００２３】
したがって、これらの式（８）〜（１１）を通気ダクト３０の出口放射音に適用すると、この放射音響パワーを最小とするスピーカ５０の最適振幅は次式のように求まる。
【００２４】
ｑ _{ｓ，ｏｐｔ}＝−Ａ ^−１ｂ〜（１２）
ここで、ベクトルｂの要素ｂｉは次のようにして求められる。
【００２５】
【数４】

【００２６】
一方、仮想騒音源ｑ _ｐの複素振幅自体は一般的には計測できないことから、このままではスピーカ５０の最適振幅を求めることができない。このため、全音響パワーＰ_ｗｔは仮想騒音源ｑ _ｐの複素振幅に対するスピーカ５０の複素振幅比の関数でも表現できることに着目し、適応制御のエラーマイクをこの受音空間Ｌに配し、このエラーマイクで検出される騒音源Ｅからの騒音とスピーカ５０からの付加音との合成音圧を最小にすることで、仮想騒音源ｑ _ｐの複素振幅に対するスピーカ５０の複素振幅比を求め、全音響パワーの最小化を図ることが考えられる。
【００２７】
しかしながら、この方法ではエラーマイクを最適配置して、はじめて音響パワーが最小になるものであることから、エラーマイクで検出される合成音圧が最小になっても、必ずしも、全音響パワーＰ_ｗｔが最小になるとは限らない。したがって、騒音源位置の同定を含めてエンジニアリングが必要になる。
【００２８】
例えば、通気ダクト３０の出口での複素振幅が仮想騒音源ｑ _ｐの複素振幅に相当することから、Ｍ個すべての特性を事前に調査し、これを入力条件にして、エラーマイクの最適配置を計算で求めることになる。このため、このエラーマイクの配置も、Ｍ個すべての音源調査結果で決めることになり、非効率的で、かつ、拡張性に欠けるという問題を生じてしまう。
【００２９】
そこで、本能動消音装置１０では仮想騒音源ｑ _ｐの複素振幅を計測する代わりに、Ｍ個の音圧検出用マイク４０を予め通気ダクト３０内部に搭載し、リアルタイムで計測している。なお、騒音が通気ダクト３０内部を伝播して通気ダクト３０出口から外部に放射されるまでの時間と、音圧検出用マイク４０で通気ダクト３０内部の騒音を検出し、スピーカ５０で放射するまでの時間が一致しなければ、通気ダクト３０出口で仮想騒音源Ｐからの騒音（通気ダクト放射音）とスピーカ５０からの付加音（スピーカ放射音）とを干渉させることができず消音を行うことができない。このため、この時間ずれの補正を行うために、図２に示すようにｉ番目のマイクから通気ダクト出口までの伝達関数をＣｉとし、スピーカ特性をＧｉとした場合のＣｉ／Ｇｉの伝達関数を音圧検出用マイク４０出力後段に設けフィルタリング処理を行っている。このフィルタリング処理された値をＸｉとすると、次式となる。
【００３０】
【数５】

【００３１】
ここで、ｊ番目の仮想騒音源Ｐとｉ番目のスピーカ５０間の距離ｒ_ＰｊＳｉは音響フィルタユニット２０を設計した時点で決まることから事前に計算可能である。従来は、騒音源Ｅの位置に関しても調査しなければ知ることはできない。マトリクスＡの要素にあたるスピーカ５０の距離も同様であり、予め各通気ダクト３０（音源の位置）がわかっていることから、設計段階でスピーカ５０を設ける位置も見積もれ、事前に付加音源間距離も把握できる。このようにして、逆行列計算を行い、スピーカ５０からの付加音の最適振幅・位相を求めることが可能となる。
【００３２】
上述したように、本実施の形態に係る能動消音装置１０によれば、騒音源Ｅにおける騒音の音圧や位相計測をすることなく、かつ、エラーマイクを使用することなく、振幅・位相特性が無相関分布を呈する面音源に対してもリアルタイムで３次元空間の全域消音を行うことが可能となる。
【００３３】
次に、通気ダクト３０とスピーカ５０との数が一致し、かつ、スピーカ５０を通気ダクト３０出口外側に設置するとともに、放射面の向きを外向きに設置した場合について説明する。
【００３４】
前述の全音響パワー理論で扱うスピーカ５０は点音源であることが条件とされているが、点音源自体は音の進行方向が音源まわりで全て一様な無指向性音源である。しかしながら、一般的なスピーカ５０は何らかの指向性を有しており、付加音の進行方向は周囲均一ではない。仮にスピーカ５０を通気ダクト３０出口外側に設置しても、放射面の向きが通気ダクト３０に対向させた場合は、その音の一部は通気ダクト３０内部にも進入し、共鳴や音圧検出用マイク４０が検知しハウリングの原因にもなる。そこで、これらを防止するために、スピーカ５０の放射面は通気ダクト３０の出口に対して外向きに設置することが好ましい。
【００３５】
また、スピーカ５０の個数に関しては、全音響パワーを最小するためには必ずしも、仮想騒音源Ｐの数と一致される必要はないものの、同じ個数、すなわち通気ダクト３０毎に１個のスピーカ５０を設置することにすれば、途中で低減対象である騒音源Ｅの規模が変わったことに伴い、通気ダクト３０の数を増設して音響フィルタユニット２０を拡張しても、はじめからスピーカ５０の個数の最適計算もしなくて済み、設計上の手間が省けるというメリットがある。
【００３６】
なお、仮にＭ個のスピーカ５０のうち、結果的に不要なスピーカ５０があっても、この場合は自動的にこのスピーカ５０からの付加音の振幅は小さくなることから、能動消音装置１０における振幅・位相算出部１０３におけるアルゴリズムを変えることなく、消音が可能である。
【００３７】
なお、本発明は上記実施形態そのままに限定されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより、種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。さらに、異なる実施形態にわたる構成要素を適宜組み合わせてもよい。
【００３８】
【発明の効果】
本発明によれば、低減対象音源の音圧や位相計測をすることなく、かつ、エラーマイクを使用することなく、振幅・位相特性が無相関分布を呈する面音源に対してもリアルタイムで３次元空間の全域消音を行うことが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る能動消音装置の構成を示す図。
【図２】同能動消音装置に組み込まれた音響フィルタユニットを示す要部正面図。
【図３】同能動消音装置による消音原理を示す説明図。
【符号の説明】
１０…能動消音装置、２０…音響フィルタユニット、３０…通気ダクト、４０…音圧検出用マイク、５０…スピーカ、１００…制御部、１０１…変動係数算出部、１０２…固定係数記憶部、１０３…振幅・位相算出部。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active silencer for reducing noise generated from a sound source to be reduced, such as a noise source, and particularly relates to a surface sound source whose amplitude and phase characteristics exhibit an uncorrelated distribution, and a sound radiated from an opening. It relates to what is suitable for.
[0002]
[Prior art]
As an active noise reduction method in a three-dimensional space for a surface sound source whose amplitude and phase characteristics exhibit an uncorrelated distribution, a method in which a plurality of microphones and speakers (additional sound sources) are used to locally mute the sound is known. However, there is no known device that silences the entire area from the source. In the case where the surface sound source can be observed at the duct opening, the sound source distribution is converted to a point sound source group by inserting a partition plate inside the duct and adjusting the partition interval so that the sound becomes a plane wave inside each partition. In some cases, active control is possible.
[0003]
[Patent Document 1]
JP-A-2002-303114
[Patent Document 2]
JP-A-6-153920
[Problems to be solved by the invention]
The above-described active noise reduction method has the following problems. In other words, in order to mute the entire space, sound pressure and phase must be measured for each partition, and based on this, an error microphone (control microphone used for adaptive control) is used to optimize the position of this microphone. It is necessary to make calculations to achieve this. That is, the acoustic power, which is the optimal evaluation function for leading the whole-area silencing, is a function of the microphone position (sound pressure minimum point).
[0006]
Therefore, the present invention provides a real-time three-dimensional space for a surface sound source whose amplitude and phase characteristics show an uncorrelated distribution without measuring the sound pressure and phase of the sound source to be reduced and without using an error microphone. It is an object of the present invention to provide an active silencer capable of performing silencing in all areas.
[0007]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the active noise reduction device of the present invention is configured as follows.
[0008]
(1) In an active silencer for reducing a sound to be reduced emitted from a sound source to be reduced, a plurality of ventilation ducts whose entrances are respectively opposed to the sound source to be reduced are arranged, and each of the ventilation ducts is arranged inside the ventilation duct. A sound pressure detection microphone, a plurality of additional sound sources arranged on the outlet side of the ventilation duct, a fixed coefficient calculating unit determined by a distance between the additional sound sources, a distance between the ventilation duct and the additional sound source, and the sound. A variation coefficient calculation unit that calculates a variation coefficient based on the sound pressure from the pressure detection microphone, and based on the fixed coefficient and the variation coefficient, to minimize the sound power of the sound radiated from the vent duct outlet. And an amplitude / phase calculator for driving the additional sound source.
[0009]
(2) The active noise reduction device according to (1), wherein the number of the ventilation ducts and the sound pressure detection microphones is M, the number of the additional sound sources is N, and the number of the i-th and j-th additional sound sources is between distance r _{SiSj of, j-th} of the noise source and the i-th distance r _PjSi between the additional sound _source, the pure imaginary v, the angular frequency ω, the air density ρ, for the wave number k, out of the i-th sound pressure The transfer function from the microphone to the outlet of the i-th ventilation duct is Ci, the output characteristic of the i-th additional sound source is Gi, the elements of the matrix A are a _ij , the elements of the vector b are b ' _i , and the microphone output for sound pressure detection. the signal multiplied by the transfer function Ci / Gi to signal Xj, the optimum amplitude of the additional sound source is taken as q _{s, opt,}
(Equation 2)

Is satisfied.
[0010]
(3) The active noise reduction device according to (1), wherein the number of the additional sound sources is the same as the number of the ventilation ducts, and the additional sound source is disposed outside an outlet of the ventilation duct. The sound is radiated toward the outside of the ventilation duct.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an active silencer 10 according to one embodiment of the present invention. The active noise reduction device 10 attempts to reduce the sound pressure level in the sound receiving space L by causing the additional sound to interfere with the noise generated from the noise source E. The active noise reduction device 10 includes an acoustic filter unit 20 installed near the noise source E, and a control unit 100 that controls each unit of the acoustic filter unit 20. In the drawing, E indicates a noise source (a sound source to be reduced), and P indicates a virtual noise source.
[0012]
The acoustic filter unit 20 includes: M ventilation ducts 30 arranged in a matrix; M sound pressure detection microphones 40 arranged inside the ventilation ducts 30 and on the respective noise source E sides; And N speakers 50 arranged on the sound receiving space L side of the ventilation duct 30 to generate additional sound. Note that N is set to 2 or more and M or less.
[0013]
The ventilation duct 30 is set so that its cross-sectional dimension (long side) is less than half the wavelength of the noise from the noise source E, and its depth dimension (the traveling direction of the sound) is not less than half the wavelength of the noise. When set in this way, noise from the noise source E having a radiation characteristic whose amplitude and phase are uncorrelated is transmitted by a plane wave inside the ventilation duct 30, At the exit of the duct 30, it can be approximated as a point source radiation. Further, a filter for correcting a time lag is provided at a stage subsequent to the output of the sound pressure detection microphone 40 as described later.
[0014]
The control unit 100 includes a variation coefficient calculation unit 101 that calculates a variation coefficient based on the distance between each ventilation duct 30 and each speaker 50 and each sound pressure level from the M sound pressure detection microphones 40; A fixed coefficient storage unit 102 that stores a fixed coefficient determined by a distance between the speakers 50, and an amplitude / phase calculation unit 103 that calculates the amplitude / phase of the additional sound by the speaker 50 based on the fixed coefficient and the variation coefficient. I have. The amplitude / phase calculation unit 103 performs a calculation to minimize the sound power of the sound radiated from each ventilation duct 30 by processing the calculation of the variation coefficient calculation unit 101 in real time.
[0015]
In the active silencer 10 configured as described above, silencing is performed as follows. That is, the noise from the noise source E enters each ventilation duct 30 of the acoustic filter unit 20. The sound pressure signal detected by the sound pressure detection microphone 40 arranged in each ventilation duct 30 is input to the variation coefficient calculation unit 101. The variation coefficient calculator 101 calculates a variation coefficient b and inputs the variation coefficient b to the amplitude / phase calculator 103. On the other hand, the fixed coefficient A is input from the fixed coefficient storage unit 102 to the amplitude / phase calculation unit 103.
[0016]
The amplitude / phase calculation unit 103 calculates the amplitude and phase of the additional sound from the speaker 50 so as to minimize the sound radiated from each ventilation duct 30 based on the variation coefficient b and the fixed coefficient A , and calculates the calculation result. The additional sound is generated based on.
[0017]
Next, a method of calculating the additional sound in the active silencer 10 will be described. Here, the distance between the i-th and j-th speakers 50 is r _SiSj , the distance between the j-th virtual noise source P and the i-th speaker 50 is r _PjSi , the pure imaginary number is v, the angular frequency is ω, and the air density is , The wave number k, the transfer function from the i-th sound pressure detecting microphone 40 to the outlet of the i-th ventilation duct 30 is Ci, the output characteristic of the i-th additional sound source is Gi, the elements of the matrix A are a _ij , element b _'i of the vector b, and the signal multiplied by the transfer function Ci / Gi output signal of the sound pressure Deyo microphone 40 Xj, optimal amplitude q _s speaker _50, and _opt.
[0018]
The amplitude and phase of the additional sound are affected by the manner of incidence on the ventilation duct 30 and the characteristics of the noise source E itself, and although not all M coincide with each other, the noise source characteristic is obtained by the acoustic filter unit 20. Are converted into a group of discrete point sound sources by M virtual noise sources P having different complex amplitudes.
[0019]
The total sound power P _wt consisting of the noise from the M virtual noise sources P and the additional sounds from the N speakers 50 can be expressed as follows. Incidentally, _{q S} is the complex amplitude (volume velocity) vector of the speaker 50, the _{q p} complex amplitude (volume velocity) vector of the virtual noise source P, b, c are likewise complex vectors, A, D denotes a matrix . Further, Re indicates a complex real part and H indicates a conjugate transpose.
[0020]

_{^{_{_{q S T = (q S1 q}}}} S2 ... q Sn) ~ (5)
^{_{_{b T = (b 1 b 2}}} ... b n) ~ (6)
^{_{_{c T = (c 1 c 2}}} ... c n) ~ (7)
The first term of the equation (4) is the sound power when only the additional sound source sounds alone, the fourth term is the sound power when only the noise source sounds alone, and the second and third terms are virtual noise sources. This corresponds to sound power generated by interference between P and the additional sound source 50.
[0021]
Also elements _{a ij} of the matrix A, the elements _{d ij} of the vector b, the elements of c _b i, _{c i} and matrix D can be described as follows.
[0022]
[Equation 3]

[0023]
Therefore, when these equations (8) to (11) are applied to the sound radiated from the outlet of the ventilation duct 30, the optimum amplitude of the speaker 50 that minimizes the radiated sound power is obtained as follows.
[0024]
_{^{q s, opt = - A -1}} b ~ (12)
Here, the element bi of the vector b is obtained as follows.
[0025]
(Equation 4)

[0026]
On the other hand, can not be measured is the complex amplitude itself generally virtual noise source q _p, it is impossible to obtain the optimum amplitude of the speaker 50 in this state. Therefore, the total sound power P _wt is focused on can be expressed in function of the complex amplitude ratio of the loudspeaker 50 for the complex amplitude of the virtual sound sources q _p, arranged error microphone adaptive control to the sound receiving space L, the error the synthesis sound pressure of the addition sound from the noise and speaker 50 from noise source E that is detected by the microphone to minimize obtains a complex amplitude ratio of the loudspeaker 50 for the complex amplitude of the virtual sound sources q _p, all the acoustic It is conceivable to minimize the power.
[0027]
However, in this method, the sound power is minimized only after the error microphone is optimally arranged. Therefore, even when the synthesized sound pressure detected by the error microphone is minimized, the total sound power P _wt is not necessarily reduced. It is not always the minimum. Therefore, engineering including identification of the noise source position is required.
[0028]
For example, since the complex amplitude at the outlet of the ventilation duct 30 corresponds to the complex amplitude of the virtual sound sources q _p, investigated beforehand all M properties, and this input condition, the optimal placement of the error microphone It will be calculated. For this reason, the arrangement of the error microphones is also determined based on the sound source investigation results of all M sound sources, which causes a problem of inefficiency and lack of expandability.
[0029]
Therefore, instead of measuring the complex amplitude of the active silencer device 10, the virtual noise source q _p, equipped with the M sound pressure Deyo microphone 40 in advance ventilation ducts 30 therein, are measured in real time. The time required for the noise to propagate through the inside of the ventilation duct 30 and be radiated from the outlet of the ventilation duct 30 to the outside, and the time until the noise inside the ventilation duct 30 is detected by the sound pressure detection microphone 40 and radiated by the speaker 50 If the times do not coincide, the noise from the virtual noise source P (radiation sound from the ventilation duct) and the additional sound from the speaker 50 (radiation sound from the speaker) cannot interfere with each other at the exit of the ventilation duct 30, and the sound is muted. Can not. Therefore, in order to correct this time lag, as shown in FIG. 2, the transfer function from the i-th microphone to the outlet of the ventilation duct is Ci, and the transfer function of Ci / Gi when the speaker characteristic is Gi is shown in FIG. A filtering process is performed after the output of the microphone 40 for sound pressure detection. Assuming that the filtered value is Xi, the following equation is obtained.
[0030]
(Equation 5)

[0031]
Here, the distance r _PjSi between the j-th virtual noise source P and the i-th speaker 50 can be calculated in advance because it is determined when the acoustic filter unit 20 is designed. Conventionally, the position of the noise source E cannot be known without investigation. The same applies to the distance of the speaker 50, which is an element of the matrix A. Since the positions of the ventilation ducts 30 (the positions of the sound sources) are known in advance, the positions at which the speakers 50 are provided at the design stage can be estimated, and the distance between the additional sound sources can be grasped in advance. it can. In this way, it is possible to perform the inverse matrix calculation and obtain the optimum amplitude and phase of the additional sound from the speaker 50.
[0032]
As described above, according to the active noise reduction device 10 according to the present embodiment, the amplitude and phase characteristics can be reduced without measuring the sound pressure and phase of the noise at the noise source E and without using an error microphone. It is also possible to perform real-time silencing in a three-dimensional space even for a surface sound source having an uncorrelated distribution.
[0033]
Next, a case will be described in which the numbers of the ventilation ducts 30 and the speakers 50 are the same, and the speakers 50 are installed outside the exit of the ventilation duct 30 and the direction of the radiation surface is outward.
[0034]
The speaker 50 used in the above-described all-sound power theory is required to be a point sound source, but the point sound source itself is an omnidirectional sound source in which the traveling direction of the sound is all uniform around the sound source. However, the general speaker 50 has some directivity, and the traveling direction of the additional sound is not uniform in the surroundings. Even if the speaker 50 is installed outside the exit of the ventilation duct 30, if the direction of the radiation surface is opposed to the ventilation duct 30, a part of the sound also enters the inside of the ventilation duct 30, and the resonance and the sound pressure are detected. The microphone 40 detects the signal and causes howling. Therefore, in order to prevent these, it is preferable that the radiating surface of the speaker 50 is installed outward with respect to the outlet of the ventilation duct 30.
[0035]
Although the number of speakers 50 does not necessarily need to be equal to the number of virtual noise sources P in order to minimize the total acoustic power, the same number, that is, one speaker 50 for each ventilation duct 30 is used. If the noise source E to be reduced is changed on the way, even if the number of ventilation ducts 30 is increased and the acoustic filter unit 20 is expanded, the number of the speakers 50 will be reduced from the beginning. There is a merit that it is not necessary to perform the optimal calculation of, and the trouble of designing can be saved.
[0036]
Even if there is an unnecessary speaker 50 among the M speakers 50, the amplitude of the additional sound from the speaker 50 is automatically reduced in this case. -The sound can be muted without changing the algorithm in the phase calculation unit 103.
[0037]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.
[0038]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, without measuring the sound pressure and phase of the sound source to be reduced, and without using an error microphone, even in the case of a surface sound source whose amplitude and phase characteristics show an uncorrelated distribution, it is possible to perform three-dimensional processing in real time. It is possible to mute the whole area of the space.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an active silencer according to one embodiment of the present invention.
FIG. 2 is an essential part front view showing an acoustic filter unit incorporated in the active silencer.
FIG. 3 is an explanatory view showing a principle of silencing by the active silencer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Active silencer, 20 ... Acoustic filter unit, 30 ... Ventilation duct, 40 ... Microphone for sound pressure detection, 50 ... Speaker, 100 ... Control part, 101 ... Variation coefficient calculation part, 102 ... Fixed coefficient storage part, 103 ... Amplitude / phase calculation unit.

Claims

In an active silencer that reduces a sound to be reduced emitted from a sound source to be reduced,
A plurality of ventilation ducts arranged with their entrances facing the sound source to be reduced,
Sound pressure detection microphones respectively arranged inside the ventilation duct,
A plurality of additional sound sources arranged on the vent duct outlet side,
A fixed coefficient calculation unit determined by the distance between the additional sound sources,
A variation coefficient calculation unit that calculates a variation coefficient based on the distance between the ventilation duct and the additional sound source and the sound pressure from the sound pressure detection microphone,
And an amplitude / phase calculation unit that drives the additional sound source based on the fixed coefficient and the variation coefficient so as to minimize the sound power of the sound radiated from the ventilation duct outlet. Silencer.

The number of the ventilation duct and the sound pressure detecting microphone is M, the number of the additional sound sources is N, the distance between the i-th and j-th additional sound sources is _rSiSj , and the distance between the j-th noise source and the i-th additional sound source is _Is the distance of r _PjSi , the pure imaginary number is v, the angular frequency is ω, the air density is ρ, the wave number is k, the transfer function from the i-th sound pressure detection microphone to the i-th vent duct outlet is Ci, and the i-th Gi is the output characteristic of the additional sound source, a _{ij is} the element of the matrix A, b ' _{i is} the element of the vector b, Xj is the signal obtained by multiplying the microphone output signal for sound pressure detection by the transfer function Ci / Gi, When the optimal amplitude is q _{s, opt} ,

The active noise reduction device according to claim 1, wherein the active noise reduction device satisfies the following.

The number of the additional sound sources is the same as the number of the ventilation ducts,
2. The active noise reduction device according to claim 1, wherein the additional sound source is disposed outside an outlet of the ventilation duct, and the sound radiates toward the outside of the ventilation duct. 3.