JP2004116503A

JP2004116503A - Duct with acoustic impedance adjusting mechanism, and electronic silencing system applying the same

Info

Publication number: JP2004116503A
Application number: JP2002316853A
Authority: JP
Inventors: Naoki Kino; 木野　直樹; Susumu Tanaka; 田中　進
Original assignee: Shizuoka Prefecture
Current assignee: Shizuoka Prefecture
Priority date: 2002-09-25
Filing date: 2002-09-25
Publication date: 2004-04-15
Anticipated expiration: 2022-09-25
Also published as: JP4171824B2

Abstract

<P>PROBLEM TO BE SOLVED: To adjust acoustic impedance in a frequency band that is required to be silenced. <P>SOLUTION: In a duct with sound impedance adjusting mechanism installed in an exhaust duct DC connected to a noise sound source NS at one end, and an electronic silencing system applying this duct, the duct is bent in a middle part, a projecting portion D3 is provided on a bent part AG, and a mechanism capable of adjusting the length of the projecting portion D3 is provided. In a direction from an upstream side to a down stream side of exhaust flow in the exhaust duct DC, a noise detecting microphone OM is installed in a position downstream to the bent part AG, and a secondary sound source SS is installed in a position downstream to the noise detecting microphone OM in the exhaust duct DC, and an error detecting microphone EM is installed downstream in a position to the secondary sound source SS in the exhaust duct DC. Sound waves received by the noise detecting microphone OM and the error detecting microphone EM are processed by an adaptive digital filter computing device F1, and generated from the secondary sound sours SS as sound waves for silencing. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】この発明は、消音したい周波数帯域の音響インピーダンスを、消音し易いように調節する機構を具備する音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムに関する。
【０００２】
【従来の技術】図１は、一般的なダクト並びに電子消音システムの構成を概略的に示しており、消音用の音波を発生する二次音源を挟んで騒音検出マイクと誤差検出マイクとを排気ダクトに沿って配置したものである。このシステムは、ダクト内の騒音と逆相の音波をダクト内に放音し、騒音を打ち消すようにしたものである。同図において、排気ダクトＤＣの一端に騒音源ＮＳが配置されており、排気ダクトＤＣ内の排気の流れの上流から下流へ向かって、騒音検出マイクＯＭ、二次音源ＳＳ、誤差検出マイクＥＭがこの順に配置され、騒音検出マイクＯＭ並びに誤差検出マイクＥＭの出力信号は適応型ディジタルフィルター演算装置Ｆ１で処理された後、二次音源ＳＳへ与えられる。
【０００３】適応型ディジタルフィルター演算装置Ｆ１においては、騒音検出マイクＯＭで受信した音波を表すアナログ信号は、ディジタル信号へ変換されてから、適応型ディジタルフィルター演算装置Ｆ１によって処理された後、アナログ信号へ変換され、二次音源ＳＳへ与えられて消音用の音波として排気ダクトＤＣ内へ放音される。
【０００４】適応型ディジタルフィルター演算装置Ｆ１は誤差検出マイクＥＭからのアナログ出力信号をディジタル変換した信号をエラー信号として受け取る。適応型ディジタルフィルター演算装置Ｆ１は、エラー信号が最小になるように、ディジタルフィルターの係数を決定する。
【０００５】排気ダクト内においては、ダクトの構造やダクト内温度によって音響インピーダンスの大きい周波数帯域、並びに小さい周波数帯域が生じる。消音したい周波数帯域の音響インピーダンスが小さい周波数帯域においては、二次音源ＳＳにアナログ信号を入力しても、二次音源ＳＳからの音波が排気ダクト内に放音され難い状態であるから、所望の消音効果を得ることはできないうえ、制御が不安定になる等の不都合が生じる。
【０００６】また、設計段階では、排気ダクト内の温度変化や騒音源を有する機器等の内部のダクト構造が把握出来ないため、騒音検出マイクＯＭ、二次音源ＳＳ、誤差検出マイクＥＭの取り付け位置を特定することができず、現場での測定によって設置位置を決定しなければならなかった。
【０００７】しかしながら、実際の現場では、騒音検出マイクＯＭ、二次音源ＳＳ、誤差検出マイクＥＭの取り付け位置の変更だけでは成果が得られず、排気ダクトの長さを調整して音響インピーダンスを調節する必要が生じる場合もあるが、騒音源となる機器、排気ダクトの屋外への排気口の設置場所が変えられないため、施工した排気ダクトの長さを施工した範囲内の伸縮のみで調整することは、困難であり、消音したい周波数帯域の音響インピーダンスを調節する問題の解決が急がれていた。
【０００８】
【発明が解決しようとする課題】この発明は上記の種々の課題を解決するために成されたもので、この発明は、消音したい周波数帯域の音響インピーダンスを調節する機構を付加することにより消音効果を向上させることができる音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムを提供することを目的とする。
【０００９】
【課題を解決するための手段】上記の目的を達成するために、この発明は、一端が騒音源を有する機器等に接続された排気ダクトに、前記騒音源から排気の流れの方向に折り曲げ部並びに突出部、騒音検出マイク、二次音源、誤差検出マイクがこの順に設置され、前記騒音検出マイク並びに前記誤差検出マイクの受信した音波を処理して前記二次音源から消音用の音波を発生させる電子消音システムであって、途中が折り曲げられた個所に設置された突出部の長さが調節可能な機構により、排気ダクトの音響インピーダンスを調節する機能を備えることを特徴とする音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムを提供する。
【００１０】この発明の電子消音システムは、一つの実施の形態においては、一端が騒音源を有する機器等に接続され、途中が折り曲げられていて、この折り曲げられた個所に長さが調節可能な突出部が設けられた排気ダクトに設置される電子消音システムであって、前記折り曲げられた個所の下流側に設置された騒音検出マイクと、前記排気ダクトの、前記騒音検出マイクに対して下流側の位置に設置された二次音源と、前記排気ダクトの、前記二次音源に対して下流側の位置に設置された誤差検出マイクと、前記騒音検出マイク並びに前記誤差検出マイクが受信した音波を処理して、前記二次音源から消音用の音波を発生させる適応型ディジタルフィルター演算装置と、を具備する。
【００１１】前記長さが調節可能な突出部は、前記排気ダクト内温度が一定の場合、並びに温度変化が少ない場合は、手動による長さ調節機構を備えればよいが、前記排気ダクト内温度が大きく変わる場合は、温度変化に応じた自動による長さ調節機構を備えてもよい。また、前記突出部は騒音源から折り曲げ部方向の延長上でも、開口端から折り曲げ部方向の延長上でも効果のある方向に設置すればよい。
【００１２】前記長さが調節可能な突出部によって、消音したい周波数帯域の音響インピーダンスが改善され、前記排気ダクトの、前記二次音源から消音したい周波数帯域の音波を発生させ易くする。
【００１３】
【発明の実施の形態】以下、この発明の一つの実施の形態を図２を参照して説明し、この発明の一つの応用例を図３〜図７を参照して説明する。なお、図２〜図７において、図１に示す構成要素と同じ又は同様の構成要素には同一の参照符号を付すことにする。
【００１４】まず、この発明の一つの実施の形態について、図２を参照しながら説明する。
【００１５】図２において、一端が騒音源ＮＳに接続された排気ダクトＤＣは、途中の個所で任意の角度（図２においては９０度）に折り曲げられ、折り曲げ個所を挟んで第１のダクト部Ｄ１と第２のダクト部Ｄ２と突出部Ｄ３から成る。排気ダクトＤＣの折り曲げ角度としては、図２においては９０度（直角に折り曲げた場合）としたが、更に深い角度や、更に緩い角度であっても良い。突出部Ｄ３の突出方向は、図２においては、騒音源ＮＳから折り曲げ部ＡＧ方向の延長としたが、開口端ＫＯから折り曲げ部ＡＧ方向の延長であっても良い。排気ダクトＤＣの途中を折り曲げて、突出部Ｄ３の長さを調節することによって、ダクト内の音響インピーダンスを変化させることができる。この発明は、ダクトの長さが変化することにより、ダクト内の音響インピーダンスが変化するという性質を利用する。
【００１６】排気ダクトＤＣの折り曲げ個所に、図２に示すように、突出部Ｄ３が設けられる。排気ダクトＤＣ内の排気の流れの上流から下流へ向かって折り曲げ部ＡＧ並びに突出部Ｄ３、騒音検出マイクＯＭ、二次音源ＳＳ、誤差検出マイクＥＭがこの順に配置され、騒音検出マイクＯＭ並びに誤差検出マイクＥＭの出力信号は適応型ディジタルフィルター演算装置Ｆ１で処理された後、二次音源ＳＳへ与えられる。
【００１７】突出部Ｄ３の長さを調節する方法は、二次音源ＳＳから、排気ダクトＤＣ内へ広帯域音を放音し、その時の誤差検出マイクＥＭの信号の周波数特性を観測し、消音したい帯域の音圧レベルが出来るだけ高くなるように、突出部Ｄ３の長さを変化させて、最適な長さに設定する。
【００１８】また、排気ダクトＤＣ内温度が大きく変化する場合には、温度変化を検出して、突出部Ｄ３の長さを自動制御する機構を備えることにより、温度変化に追従した最適な音響インピーダンスを得ることが出来る。
【００１９】突出部Ｄ３の長さは、騒音源を有する機器の内部ダクト長と排気ダクト長を合わせた全長と温度変化に対して、調節された結果、二次音源ＳＳからの消音したい帯域の信号が排気ダクトＤＣ内へ放音され易くなり、確実に消音効果を得ることが可能になるばかりでなく、制御も安定になる。
【００２０】次に、この発明の一つの応用例について、図３〜図７を参照しながら説明する。
【００２１】工場内にある電機装置の排気ダクトシステムに公知の電子消音システムを設置した応用例を図３に示す。騒音源ＮＳから放出される排気騒音を消音したいが、消音したい周波数帯域の音響インピーダンスが小さい場合、消音出来ないことがある。
【００２２】二次音源ＳＳから放音された広帯域音を監視マイクＥＭで観測した周波数特性を図５に示す。図５に示す発明前のダクトのデータから、６０ヘルツ付近の信号レベルが低い、つまり、音響インピーダンスが小さいことが読み取れる。
【００２３】実際に騒音源ＮＳの電機装置を稼動し、公知の電子消音システムを動作させた結果、開口端ＫＯで測定した周波数特性を図６に示すが、消音を希望する騒音レベルが大きい６０ヘルツ付近では、消音効果が得られていないことがわかる。
【００２４】そこで、この発明に係る電子消音システムを工場内にある電機装置の排気ダクトシステムに設置した応用例を図４に示す。
【００２５】二次音源ＳＳから広帯域音を放音し、監視マイクＥＭで周波数特性を観測しながら、突出部Ｄ３の長さを調節し、消音したい帯域である６０ヘルツ付近の音響インピーダンスを大きくとった結果の周波数特性を図５に示す。
【００２６】図５に示す発明後のダクトのデータから、６０ヘルツ付近の信号レベルが、発明前のダクトのデータより約２０デシベル高い、つまり、音響インピーダンスが大きくなったことが読み取れる。
【００２７】実際に騒音源ＮＳの電機装置を稼動し、この発明に係る電子消音システムを動作させた結果、開口端ＫＯで測定した周波数特性を図７に示すが、消音を希望した騒音レベルが大きい６０ヘルツ付近でも、約３０デシベルの消音効果が得られたことがわかる。
【００２８】このように、この発明の応用例の電子消音装置によれば、排気ダクトＤＣの途中が折り曲げられた個所ＡＧに設置された突出部Ｄ３の長さを調節することにより、排気ダクトＤＣの音響インピーダンスを調節することが可能となり、消音したい周波数帯域の音響インピーダンスを大きくすることで、排気ダクトＤＣの二次音源ＳＳから、消音したい周波数帯域の音波が排気ダクト内に放音し易くなり、確実に消音したい帯域の消音効果を得ることができる。
【００２９】
【発明の効果】以上、この発明に係る音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムの一つの実施の形態並びに一つの応用例を説明したところから明らかなとおり、この発明によって、二次音源から放音できない周波数帯域は実質的になくなり、確実に消音したい帯域の消音効果を得ることが可能になるばかりでなく、制御も安定になるという格別の効果を得る。また、この発明は、工場内に設置した電機装置からの屋外排気ダクトシステム等のように、電機装置や屋外排気口の場所を変えられないような場合でも、音響インピーダンスを調節する必要がある場合について、最適な方法であり、工場にダクトを施工する場合に生じるダクトの曲がり部分を利用して、適用すれば格別の効果を得る。
【図面の簡単な説明】
【図１】公知のダクト並びに電子消音システムの構成を概略的に示す図である。
【図２】この発明に係る音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムの一つの実施形態の構成を概略的に示す図である。
【図３】公知のダクト並びに電子消音システムによる工場内排気ダクトシステムの応用例を示す図である。
【図４】この発明に係る音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムによる工場内排気ダクトシステムの応用例を示す図である。
【図５】工場内排気ダクトシステムで、二次音源から放音された広帯域音を監視マイクで収音した時の周波数特性について、公知のダクト並びに電子消音システムと、この発明に係る音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムとでの比較を示す図である。
【図６】工場内排気ダクトシステムで、公知のダクト並びに電子消音システムを動作させた時、ダクトの開口端で観測される消音効果を示す図である。
【図７】工場内排気ダクトシステムで、この発明に係る音響インピーダンス調節機構付きダクト並びにこれを適用した電子消音システムを動作させた時、ダクトの開口端で観測される消音効果を示す図である。
【符号の説明】
ＮＳ　騒音源
ＯＭ　騒音検出マイク
ＳＳ　二次音源
ＥＭ　誤差検出マイク
Ｆ１　適応型ディジタルフィルター演算装置
ＫＯ　開口端
ＤＣ　排気ダクト
ＡＧ　折り曲げ部
Ｄ１　騒音源から折り曲げ部までのダクト
Ｄ２　折り曲げ部から開口端までのダクト
Ｄ３　折り曲げ部に設けられた突出部[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duct with an acoustic impedance adjusting mechanism having a mechanism for adjusting the acoustic impedance of a frequency band to be silenced so that the sound can be easily silenced, and an electronic silencing system using the duct.
[0002]
2. Description of the Related Art FIG. 1 schematically shows the structure of a general duct and an electronic noise reduction system, in which a noise detection microphone and an error detection microphone are exhausted with a secondary sound source for generating sound for noise reduction interposed therebetween. It is arranged along the duct. In this system, a sound wave having the opposite phase to the noise in the duct is emitted into the duct to cancel the noise. In the figure, a noise source NS is disposed at one end of an exhaust duct DC, and a noise detection microphone OM, a secondary sound source SS, and an error detection microphone EM are arranged from upstream to downstream of the flow of exhaust gas in the exhaust duct DC. The output signals of the noise detection microphone OM and the error detection microphone EM are arranged in this order, processed by the adaptive digital filter operation device F1, and then supplied to the secondary sound source SS.
In the adaptive digital filter operation device F1, an analog signal representing a sound wave received by the noise detection microphone OM is converted into a digital signal, processed by the adaptive digital filter operation device F1, and then converted into an analog signal. The sound is supplied to the secondary sound source SS and is emitted into the exhaust duct DC as sound waves for silencing.
The adaptive digital filter operation device F1 receives a signal obtained by digitally converting an analog output signal from the error detection microphone EM as an error signal. The adaptive digital filter operation device F1 determines the coefficients of the digital filter so that the error signal is minimized.
In the exhaust duct, a frequency band having a large acoustic impedance and a frequency band having a small acoustic impedance are generated depending on the structure of the duct and the temperature in the duct. In a frequency band where the acoustic impedance of the frequency band to be silenced is small, even if an analog signal is input to the secondary sound source SS, sound waves from the secondary sound source SS are hard to be emitted into the exhaust duct. In addition to the silencing effect, there are disadvantages such as unstable control.
At the design stage, since the temperature change in the exhaust duct and the internal duct structure of equipment having a noise source cannot be grasped, the mounting positions of the noise detecting microphone OM, the secondary sound source SS, and the error detecting microphone EM are not provided. Could not be specified, and the installation position had to be determined by on-site measurement.
[0007] However, in an actual site, a change in the position of the noise detection microphone OM, the secondary sound source SS, and the error detection microphone EM alone does not produce any result, and the acoustic impedance is adjusted by adjusting the length of the exhaust duct. Although it may be necessary to adjust the length of the constructed exhaust duct only by expansion and contraction within the constructed range, it is not possible to change the installation location of the equipment that becomes the noise source and the exhaust outlet to the outside of the exhaust duct. This is difficult, and the problem of adjusting the acoustic impedance in the frequency band to be silenced has been urgently required.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned various problems, and the present invention provides a noise reduction effect by adding a mechanism for adjusting the acoustic impedance of a frequency band to be reduced. It is an object of the present invention to provide a duct with an acoustic impedance adjusting mechanism capable of improving the noise reduction and an electronic silencing system to which the duct is applied.
[0009]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an exhaust duct having one end connected to a device having a noise source or the like. In addition, a protrusion, a noise detection microphone, a secondary sound source, and an error detection microphone are installed in this order, and a sound wave received by the noise detection microphone and the error detection microphone is processed to generate a sound-absorbing sound wave from the secondary sound source. An electronic silencing system with an acoustic impedance adjustment mechanism that has a function to adjust the acoustic impedance of the exhaust duct by a mechanism that can adjust the length of the protruding part installed at the part where it was bent in the middle Provided are a duct and an electronic silencing system to which the duct is applied.
[0010] In one embodiment of the electronic silencing system of the present invention, one end is connected to a device having a noise source or the like, the middle is bent, and the length can be adjusted at the bent portion. An electronic silencing system installed in an exhaust duct provided with a protruding portion, wherein a noise detection microphone installed downstream of the bent portion, and a downstream side of the noise detection microphone of the exhaust duct. The secondary sound source installed at the position of, the exhaust duct, an error detection microphone installed at a position downstream with respect to the secondary sound source, the noise detection microphone and the sound wave received by the error detection microphone An adaptive digital filter operation device for performing processing to generate sound waves for silencing from the secondary sound source.
When the temperature inside the exhaust duct is constant and when the temperature change is small, the projecting portion whose length can be adjusted may be provided with a manual length adjusting mechanism. If the temperature changes greatly, an automatic length adjustment mechanism according to the temperature change may be provided. Further, the projecting portion may be installed in a direction that is effective even when extending from the noise source in the direction of the bent portion or in extending from the opening end in the direction of the bent portion.
The adjustable length protruding portion improves the acoustic impedance in a frequency band to be silenced, and makes it easier for the exhaust duct to generate sound waves in the frequency band to be silenced from the secondary sound source.
[0013]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. 2, and one application example of the present invention will be described with reference to FIGS. 2 to 7, the same or similar components as those shown in FIG. 1 are denoted by the same reference numerals.
First, one embodiment of the present invention will be described with reference to FIG.
In FIG. 2, an exhaust duct DC, one end of which is connected to the noise source NS, is bent at an arbitrary angle (90 degrees in FIG. 2) at an intermediate position, and the first duct portion is sandwiched between the bent portions. D1, a second duct portion D2, and a projecting portion D3. The bending angle of the exhaust duct DC is 90 degrees in FIG. 2 (when bent at a right angle), but may be a deeper angle or a gentler angle. In FIG. 2, the projecting direction of the projecting portion D3 extends from the noise source NS in the direction of the bent portion AG, but may extend from the open end KO in the direction of the bent portion AG. The acoustic impedance in the duct can be changed by bending the middle of the exhaust duct DC and adjusting the length of the protrusion D3. The present invention utilizes the property that the acoustic impedance in the duct changes as the length of the duct changes.
As shown in FIG. 2, a protruding portion D3 is provided at a bent portion of the exhaust duct DC. The bent part AG and the protruding part D3, the noise detection microphone OM, the secondary sound source SS, and the error detection microphone EM are arranged in this order from the upstream to the downstream of the flow of the exhaust gas in the exhaust duct DC, and the noise detection microphone OM and the error detection are arranged. The output signal of the microphone EM is processed by the adaptive digital filter operation device F1, and then supplied to the secondary sound source SS.
A method of adjusting the length of the protruding portion D3 is to emit a broadband sound from the secondary sound source SS into the exhaust duct DC, observe the frequency characteristics of the signal of the error detection microphone EM at that time, and mute the sound. The length of the protruding portion D3 is changed to an optimum length so that the sound pressure level of the band becomes as high as possible.
When the temperature inside the exhaust duct DC changes greatly, a mechanism for detecting the temperature change and automatically controlling the length of the protruding portion D3 is provided, so that the optimum acoustic impedance following the temperature change is provided. Can be obtained.
The length of the protruding portion D3 is adjusted with respect to the total length including the length of the internal duct and the length of the exhaust duct and the temperature change of the equipment having the noise source, and as a result, the length of the band where the sound from the secondary sound source SS is desired to be suppressed The signal is easily emitted into the exhaust duct DC, so that not only can the sound deadening effect be reliably obtained, but also the control becomes stable.
Next, one application example of the present invention will be described with reference to FIGS.
FIG. 3 shows an application example in which a known electronic silencing system is installed in an exhaust duct system of an electric machine in a factory. Although it is desired to muffle the exhaust noise emitted from the noise source NS, if the acoustic impedance of the frequency band to be muffled is small, the muffler may not be able to be muffled.
FIG. 5 shows the frequency characteristics of the broadband sound emitted from the secondary sound source SS observed by the monitoring microphone EM. From the data of the duct before invention shown in FIG. 5, it can be read that the signal level around 60 Hz is low, that is, the acoustic impedance is small.
FIG. 6 shows the frequency characteristics measured at the open end KO as a result of actually operating the electrical equipment of the noise source NS and operating the known electronic noise reduction system. It can be seen that the noise reduction effect is not obtained near Hertz.
FIG. 4 shows an application example in which the electronic silencing system according to the present invention is installed in an exhaust duct system of an electric machine in a factory.
Broadband sound is emitted from the secondary sound source SS, the length of the protruding portion D3 is adjusted while observing the frequency characteristics with the monitoring microphone EM, and the acoustic impedance around 60 Hz, which is the band to be silenced, is increased. FIG. 5 shows the frequency characteristics obtained as a result.
From the data of the duct after the invention shown in FIG. 5, it can be seen that the signal level near 60 Hz is higher than the data of the duct before the invention by about 20 dB, that is, the acoustic impedance is increased.
FIG. 7 shows the frequency characteristics measured at the open end KO as a result of actually operating the electrical equipment of the noise source NS and operating the electronic noise reduction system according to the present invention. It can be seen that a noise reduction effect of about 30 decibels was obtained even near a large 60 Hz.
As described above, according to the electronic silencer of the application example of the present invention, by adjusting the length of the protruding portion D3 installed at the point AG where the middle of the exhaust duct DC is bent, the exhaust duct DC can be adjusted. The sound impedance of the frequency band to be silenced can be easily emitted from the secondary sound source SS of the exhaust duct DC into the exhaust duct by increasing the acoustic impedance of the frequency band to be silenced. Thus, it is possible to surely obtain a silencing effect of a band to be silenced.
[0029]
As described above, one embodiment and one application example of the duct with the acoustic impedance adjusting mechanism according to the present invention and the electronic silencing system to which the duct is applied have been described. The frequency band in which sound cannot be emitted from the next sound source substantially disappears, so that not only the silencing effect of the band to be surely silenced can be obtained, but also a special effect that the control becomes stable. Further, the present invention is applicable to a case where it is necessary to adjust the acoustic impedance even in a case where the location of an electric device or an outdoor exhaust port cannot be changed, such as an outdoor exhaust duct system from an electric device installed in a factory. Is an optimal method, and a special effect can be obtained if the method is applied by using a bent portion of a duct generated when a duct is constructed in a factory.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of a known duct and an electronic silencing system.
FIG. 2 is a diagram schematically showing a configuration of one embodiment of a duct with an acoustic impedance adjusting mechanism according to the present invention and an electronic silencing system to which the duct is applied.
FIG. 3 is a diagram showing an application example of an exhaust duct system in a factory using a known duct and an electronic silencing system.
FIG. 4 is a diagram showing an application example of an exhaust duct system in a factory using a duct with an acoustic impedance adjusting mechanism according to the present invention and an electronic silencing system to which the duct is applied.
FIG. 5 is a diagram showing a known duct and an electronic noise reduction system according to the present invention, regarding a frequency characteristic when a broadband sound emitted from a secondary sound source is collected by a monitoring microphone in an exhaust duct system in a factory. It is a figure which shows the comparison with the duct with a mechanism, and the electronic silence system which applied this.
FIG. 6 is a diagram showing a noise reduction effect observed at an open end of a duct when a known duct and an electronic noise reduction system are operated in an exhaust duct system in a factory.
FIG. 7 is a diagram showing a sound deadening effect observed at the open end of the duct when the duct with the acoustic impedance adjusting mechanism according to the present invention and the electronic sound deadening system using the same are operated in the exhaust duct system in the factory. .
[Explanation of symbols]
NS Noise source OM Noise detection microphone SS Secondary sound source EM Error detection microphone F1 Adaptive digital filter arithmetic unit KO Open end DC Exhaust duct AG Bend D1 Duct D2 from noise source to bend D2 Duct D from bent to open end Projection provided on bent part

Claims

A duct with an acoustic impedance adjustment mechanism, one end of which is connected to a noise source, and which is bent in the middle, and which adjusts the acoustic impedance by adjusting the length of a protrusion provided at the bent portion.

One end is connected to a noise source, the middle is bent, and an electronic silencing system is installed in a duct that adjusts acoustic impedance by adjusting the length of a protrusion provided at the bent portion. A noise detection microphone installed at a position downstream of the bent portion of the duct, a secondary sound source installed at a position downstream of the duct with respect to the noise detection microphone, and the duct An error detection microphone installed at a downstream position with respect to the secondary sound source, processing the sound waves received by the noise detection microphone and the error detection microphone, and converting sound waves for muffling from the secondary sound source to An electronic silencing system using a duct with an acoustic impedance adjustment mechanism, comprising: an adaptive digital filter operation device for generating the noise.