JP2012237584A - Acoustic tube and acoustic property measuring apparatus - Google Patents
Acoustic tube and acoustic property measuring apparatus Download PDFInfo
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Abstract
Description
本発明は、吸音試験材の吸音率や音響インピーダンスを測定する際に用いる音響管と、この音響管を備えた音響特性測定装置に関する。 The present invention relates to an acoustic tube used when measuring a sound absorption coefficient and acoustic impedance of a sound absorption test material, and an acoustic characteristic measuring apparatus including the acoustic tube.
図６に示すように、音響特性測定装置に備えられる音響管１００は、管本体１０１の一端部に吸音試験材Ｗを保持する保持部１０２が設けられていると共に、管本体１０１の他端部に、前記保持部１０２に保持される吸音試験材Ｗへ向けて音波を発生する音源部１０３が設けられている。また、保持部１０２と音源部１０３との間の管壁（周方向の壁部）に、管軸方向に並んで２個以上のマイクロフォン１０４（コンデンサマイクロフォン）が設けられている（非特許文献１参照）。 As shown in FIG. 6, the acoustic tube 100 provided in the acoustic characteristic measuring apparatus is provided with a holding portion 102 that holds the sound absorption test material W at one end portion of the tube main body 101 and the other end portion of the tube main body 101. Further, a sound source unit 103 that generates a sound wave toward the sound absorption test material W held by the holding unit 102 is provided. In addition, two or more microphones 104 (condenser microphones) are provided on the tube wall (circumferential wall) between the holding unit 102 and the sound source unit 103 so as to be aligned in the tube axis direction (Non-Patent Document 1). reference).
音響特性測定装置は、音響管１００の保持部１０２に吸音試験材Ｗを保持させた状態で、音源部１０３により平面波である音波を発生させ、各マイクロフォン１０４で採取される音圧から２点間の複素音圧伝達関数を求め、この複素音圧伝達関数を用いて吸音試験材Ｗの吸音率や音響インピーダンスの計算を行うようにする。
なお、音響管の管中央部に遮音試験材を保持させ、且つ遮音試験材と音源部との間の管壁にもマイクロフォンを設ける構成として、吸音試験材の吸音率だけではなく、遮音試験材の遮音率を同時又は選択的に測定できるようにした音響特性測定装置も提案されている（特許文献１参照）。
The acoustic characteristic measuring device generates a sound wave that is a plane wave by the sound source unit 103 in a state where the sound absorption test material W is held by the holding unit 102 of the acoustic tube 100, and between two points from the sound pressure collected by each microphone 104. The complex sound pressure transfer function is obtained, and the sound absorption coefficient and acoustic impedance of the sound absorption test material W are calculated using this complex sound pressure transfer function.
Note that the sound insulation test material is held not only in the sound absorption coefficient of the sound absorption test material, but also in the tube wall between the sound insulation test material and the sound source part. There has also been proposed an acoustic characteristic measuring apparatus that can simultaneously or selectively measure the sound insulation rate (see Patent Document 1).
従来から用いられている音響管を利用した音響特性測定装置によって測定できる最大（上限）周波数は、５ｋＨｚ（最高でも６．４ｋＨｚ）までであった。なぜなら、最大周波数を高く設定しようとすれば、音響管の管径を細くし、しかも２箇所以上設けるマイクロフォンの設置間隔も狭くする必要がある。例えば、最大周波数を１０ｋＨｚ以上に設定する場合を想定すると、音響管の管径（内径）は１９ｍｍ未満としなければならず、またマイクロフォン間隔（中心間距離）は１５ｍｍ未満としなければならない。 The maximum (upper limit) frequency that can be measured by an acoustic characteristic measuring apparatus using a conventionally used acoustic tube is up to 5 kHz (up to 6.4 kHz). This is because if the maximum frequency is to be set high, it is necessary to reduce the tube diameter of the acoustic tube and also to reduce the interval between microphones provided at two or more locations. For example, assuming that the maximum frequency is set to 10 kHz or more, the tube diameter (inner diameter) of the acoustic tube must be less than 19 mm, and the microphone interval (center-to-center distance) must be less than 15 mm.
しかし、このように管径の細い音響管の管壁に対し、しかも狭い間隔でマイクロフォンを保持させることは困難を伴う。その結果、５ｋＨｚを超えるような高周波数域での吸音率やインピーダンスは測定することができなかったのが実情である。勿論、特許文献１で開示された音響特性測定装置でも、このような高周波数域の測定を可能とするものではない。 However, it is difficult to hold the microphone at a narrow interval with respect to the tube wall of the acoustic tube having a small tube diameter. As a result, the actual condition is that the sound absorption coefficient and impedance in a high frequency range exceeding 5 kHz could not be measured. Of course, even the acoustic characteristic measuring device disclosed in Patent Document 1 does not enable measurement in such a high frequency range.
本発明は、上記事情に鑑みてなされたものであって、５ｋＨｚを超えるような高周波数域での吸音率や音響インピーダンス測定を行えるようにした音響管及び音響特性測定装置を提供することを目的とする。 The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an acoustic tube and an acoustic characteristic measuring apparatus capable of measuring sound absorption coefficient and acoustic impedance in a high frequency range exceeding 5 kHz. And
前記目的を達成するために、本発明は次の手段を講じた。
即ち、本発明は、管本体の一端部に吸音試験材を保持する保持部が設けられていると共に管本体の他端部に前記保持部に保持される吸音試験材へ向けて音波を発生する音源部が設けられ、且つ前記保持部と音源部との間の管壁に管軸方向に並んで２個以上の集音部が設けられた音響管において、前記集音部は、前記管本体の管壁を貫通する通孔と、この通孔の管壁外面側の開口周部を拡径するように設けられた凹部と、この凹部に埋め込まれたＭＥＭＳマイクロフォンとを有しており、前記管本体の管壁内面とＭＥＭＳマイクロフォンとの間を連通する通孔の長さが、当該通孔内で前記音源部から発せられる音波の共鳴を起こす長さよりも短くなるように設定されていることを特徴とする。
In order to achieve the above object, the present invention has taken the following measures.
That is, according to the present invention, a holding portion for holding the sound absorbing test material is provided at one end of the tube main body, and a sound wave is generated toward the sound absorbing test material held by the holding portion at the other end of the tube main body. An acoustic tube provided with a sound source unit and provided with two or more sound collection units arranged in a tube axis direction on a tube wall between the holding unit and the sound source unit, wherein the sound collection unit is the tube body A through-hole penetrating the tube wall, a recess provided to expand the diameter of the opening peripheral portion of the through-hole on the tube wall outer surface, and a MEMS microphone embedded in the recess, The length of the through hole communicating between the tube wall inner surface of the tube main body and the MEMS microphone is set to be shorter than the length causing the resonance of the sound wave emitted from the sound source section in the through hole. It is characterized by.
具体的には、前記管壁内面とＭＥＭＳマイクロフォンとの間を連通する通孔の長さが、次式を満たすＬbよりも短い寸法とされたものとするのがよい。
ｆ＝ｃ／４Ｌb
但し、ｆ：音源部から発せられる音波の最大周波数
ｃ：音速
すなわち、管壁内面とＭＥＭＳマイクロフォンとの間を連通する通孔の長さをＬとおくとき、
Ｌ＜Ｌb
の関係が得られるようにする。
Specifically, the length of the hole for communicating between said tube wall inner surface and the MEMS microphone, preferably set to those shorter dimension than L b which satisfy the following equation.
f = c / 4L b
Where f: maximum frequency of sound wave emitted from the sound source
c: sound velocity That is, when the length of the through hole communicating between the inner surface of the tube wall and the MEMS microphone is set to L,
L <L b
So that the relationship can be obtained.
このような構成の音響管を備えることにより、吸音率及び／又は音響インピーダンスが測定可能な音響特性測定装置を構成することができる。 By providing the acoustic tube having such a configuration, it is possible to configure an acoustic characteristic measuring device capable of measuring the sound absorption coefficient and / or the acoustic impedance.
本発明に係る音響管及び音響特性測定装置では、５ｋＨｚを超えるような高周波数域での吸音率やインピーダンス測定を行うことができる。 With the acoustic tube and the acoustic characteristic measuring device according to the present invention, it is possible to measure the sound absorption coefficient and impedance in a high frequency range exceeding 5 kHz.
以下、本発明の実施の形態を、図面に基づき説明する。
図１は、本発明に係る音響特性測定装置３を示したものである。
音響特性測定装置３は、本発明に係る音響管１と、この音響管１から得られたデータ（音圧データ）の分析を行う演算部２とを有する。
音響管１は、管本体５の一端部に吸音試験材Ｗを保持する保持部６が設けられている。また、管本体５の他端部には、保持部６に保持される吸音試験材Ｗへ向けて音波を発生する音源部７が設けられている。保持部６と音源部７との間の管壁に、管軸方向に並んで２個以上（図例では２個）の集音部８が設けられている。
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an acoustic characteristic measuring apparatus 3 according to the present invention.
The acoustic characteristic measurement device 3 includes the acoustic tube 1 according to the present invention and a calculation unit 2 that analyzes data (sound pressure data) obtained from the acoustic tube 1.
The acoustic tube 1 is provided with a holding portion 6 for holding the sound absorption test material W at one end portion of the tube body 5. In addition, a sound source unit 7 that generates sound waves toward the sound absorption test material W held by the holding unit 6 is provided at the other end of the tube body 5. Two or more (two in the illustrated example) sound collecting portions 8 are provided on the tube wall between the holding portion 6 and the sound source portion 7 along the tube axis direction.
管本体５は、金属やプラスチックなどで形成されるか又は管壁内面が気密性を確保するために被覆処理されたストレート管（直管）であって、保持部６は、吸音試験材Ｗを周隙間無く嵌め入れて、振動を生じさせない状態に保持できるように管本体５の管端で開口する構造となっている。
音響管１（管本体５）の内径ｄは、５ｋＨｚを超えるような高周波数域での吸音率や音響インピーダンスの測定を可能にするため、８ｍｍ≦ｄ≦１９ｍｍの範囲で形成されている。また、集音部８はマイクロフォンを設置する部分であるが、５ｋＨｚを超えるような高周波数域での吸音率やインピーダンスの測定を可能にするという同じ理由から、この集音部８の相互間隔（マイクロフォンの中心間距離）Ｓは、７ｍｍ≦Ｓ≦１５ｍｍの範囲としてある。
The tube body 5 is a straight tube (straight tube) formed of metal, plastic, or the like so that the inner surface of the tube wall is coated to ensure airtightness. The tube body 5 is open at the end of the tube body 5 so that it can be fitted without a circumferential gap and kept in a state that does not generate vibration.
The inner diameter d of the acoustic tube 1 (tube body 5) is formed in a range of 8 mm ≦ d ≦ 19 mm in order to enable measurement of the sound absorption coefficient and acoustic impedance in a high frequency range exceeding 5 kHz. The sound collecting unit 8 is a part where a microphone is installed, but for the same reason that the sound absorption coefficient and impedance can be measured in a high frequency range exceeding 5 kHz, the mutual interval between the sound collecting units 8 ( The center-to-center distance (S) of the microphone is in the range of 7 mm ≦ S ≦ 15 mm.
なお、音源部７は、言うまでもなく５ｋＨｚを超えるような高周波数域（例えば１０ｋＨｚ）の音波を発生可能とされたものである。この音源部７は、前記したように管本体５が細く形成されていることに伴い、スピーカ１０を管本体５の外部に配置させてあり、このスピーカ１０に連結させたホース１１を介して、スピーカ１０からの音波を管本体５内へ導かせるようにしてある。 Needless to say, the sound source unit 7 can generate sound waves in a high frequency range (for example, 10 kHz) exceeding 5 kHz. As described above, the sound source unit 7 has the speaker 10 disposed outside the tube body 5 with the tube body 5 being formed thin, and via the hose 11 connected to the speaker 10, Sound waves from the speaker 10 are guided into the tube body 5.
図２に示すように、集音部８は、管本体５の管壁を貫通する通孔１５と、この通孔１５の管壁外面側の開口周部を拡径するように設けられた凹部１６と、この凹部１６に埋め込まれたＭＥＭＳマイクロフォン１７とを有している。
ＭＥＭＳマイクロフォン１７は、一辺が約４ｍｍ、厚さが約１ｍｍの角片状の小型マイクロフォンであって、管本体５の管内へ向けられる面の中央部に、内蔵するダイヤフラム部へ音圧を導くための小孔１８が設けられている。ＭＥＭＳマイクロフォン１７は、半導体製造技術の応用により製造される微小マイクロフォンであり、小型で耐熱性に優れた微小電気機械素子である。
As shown in FIG. 2, the sound collection unit 8 includes a through hole 15 penetrating the tube wall of the tube body 5 and a recess provided to expand the diameter of the opening peripheral portion of the through hole 15 on the tube wall outer surface side. 16 and a MEMS microphone 17 embedded in the recess 16.
The MEMS microphone 17 is a small, square-shaped microphone having a side of about 4 mm and a thickness of about 1 mm. The MEMS microphone 17 guides the sound pressure to the built-in diaphragm at the center of the surface of the tube body 5 facing the tube. A small hole 18 is provided. The MEMS microphone 17 is a micro microphone manufactured by application of semiconductor manufacturing technology, and is a micro electro mechanical element that is small and excellent in heat resistance.
このようなＭＥＭＳマイクロフォン１７の埋め込みを可能にするように、凹部１６の開口形状（円形又は角形）や開口寸法ｂが設定されており、またＭＥＭＳマイクロフォン１７の小孔１８と合致するように、凹部１６の中央部に通孔１５が配置されるようになっている。また、この凹部１６の深さは、管本体５の管壁厚さと通孔１５の長さＬ（管本体５の管壁内面とＭＥＭＳマイクロフォン１７との間の距離）とによって支配されるものであり、この通孔１５の長さＬは、後述のように設定する。 The opening shape (circular or square) and the opening dimension b of the recess 16 are set so that the MEMS microphone 17 can be embedded, and the recess is formed so as to match the small hole 18 of the MEMS microphone 17. A through hole 15 is arranged at the center of 16. The depth of the recess 16 is governed by the tube wall thickness of the tube body 5 and the length L of the through hole 15 (the distance between the tube wall inner surface of the tube body 5 and the MEMS microphone 17). Yes, the length L of the through hole 15 is set as described later.
なお、ＪＩＳ Ａ １４０５−２によれば、マイクロフォンは音響管の管壁内面と同じ高さとなるように取り付けるものとされている。しかし、本出願人は、管本体５の管壁内面とＭＥＭＳマイクロフォン１７との間に通孔１５を設けても、通孔１５の長さを、通孔１５内で音波の共鳴が起こる長さよりも短くなるように設定しておけば、ＭＥＭＳマイクロフォン１７による音圧の測定値に悪影響が出ないことを知見し、本願発明に想到するに至っている。 According to JIS A 1405-2, the microphone is attached so as to be the same height as the inner surface of the tube wall of the acoustic tube. However, even if the present applicant provides the through hole 15 between the tube wall inner surface of the tube main body 5 and the MEMS microphone 17, the length of the through hole 15 is set to be longer than the length at which acoustic resonance occurs in the through hole 15. If it is set to be shorter, the measurement value of the sound pressure by the MEMS microphone 17 will not be adversely affected, and the present invention has been conceived.
すなわち、通孔１５内で音波の共鳴が起こるときの通孔１５の長さをＬbとおいたとき、この長さＬbにより決定される最大周波数ｆは、次式のように示すことができる。
ｆ＝ｃ／４Ｌb (1)
但し、ｆ：音源部から発せられる音波の最大周波数
ｃ：音速
従って、実際に採用する通孔１５の長さＬは、式(１)で算出されるＬbよりも短い寸法（Ｌ＜Ｌb）とすればよいことになる。
That is, when the length of the through hole 15 when in the through hole 15 resonance wave occurs put the L b, the maximum frequency f which is determined by the length L b can be shown as: .
f = c / 4L b (1)
Where f: maximum frequency of sound wave emitted from the sound source
c: speed of sound
Therefore, the length L of the through-hole 15 that is actually adopted may be a dimension (L <L b ) that is shorter than L b calculated by the equation (1).
Ｌ＜Ｌbとする代わりに、式(１)のｆを、実際に測定しようとする上限周波数より高い周波数に設定してもよい。例えば、上限周波数を１０ｋＨｚとする場合には、最大周波数ｆを２０ｋＨｚなどとおいてＬbを求め、このＬbに基づいて通孔１５の長さＬを決定するようにするとよい。
なお、ＭＥＭＳマイクロフォン１７を管本体５の管壁内面と同じ高さになるように取り付けたと仮定すると（即ち、Ｌ＝０）、凹部１６の内周面とＭＥＭＳマイクロフォン１７の外周部との周隙間を完全に密封することが困難となることから、この周隙間を介した音漏れが起こるおそれがある。このような音漏れが起こると正確な測定ができないため、この点で、通孔１５を設けること（即ち、通孔１５の長さＬを所定長さ以上にすること）は必要と言える。
L <Instead of the L b, f on the equation (1) may be set to a frequency higher than the upper limit frequency to be actually measured. For example, when the upper limit frequency is 10 kHz, the maximum frequency f is set to 20 kHz or the like, L b is obtained, and the length L of the through hole 15 is determined based on this L b .
Assuming that the MEMS microphone 17 is attached so as to have the same height as the inner surface of the tube wall of the tube body 5 (that is, L = 0), the circumferential gap between the inner peripheral surface of the recess 16 and the outer peripheral portion of the MEMS microphone 17 Since it is difficult to completely seal the sound, there is a risk of sound leakage through the circumferential gap. Since accurate measurement cannot be performed when such sound leakage occurs, it can be said that it is necessary to provide the through-hole 15 at this point (that is, to make the length L of the through-hole 15 longer than a predetermined length).
具体例として、前記のように最大周波数ｆを２０ｋＨｚとおく場合は、Ｌbが４ｍｍより少し長い程度となる。そこで、長さＬの上限を４ｍｍとする。また、ＪＩＳ Ａ １４０５−２において音響管の管壁厚さは、音響信号による振動を生じず、且つ振動共振を生じないことの条件として管外径Ｄ（ｍｍ）の５％が推奨されている。そこで、長さＬ（ｍｍ）の下限も、音響管１（管本体５）の管外径Ｄの５％を採用するものとした。すなわち、通孔１５の長さＬは、次式、
０．０５Ｄ≦Ｌ≦４ｍｍ
で設定するものとした。
As a specific example, the case 20kHz far the maximum frequency f as, L b is the degree slightly longer than 4 mm. Therefore, the upper limit of the length L is 4 mm. In addition, in JIS A 1405-2, the tube wall thickness of the acoustic tube is recommended to be 5% of the tube outer diameter D (mm) as a condition that vibration due to an acoustic signal does not occur and vibration resonance does not occur. . Therefore, 5% of the outer diameter D of the acoustic tube 1 (tube body 5) is adopted as the lower limit of the length L (mm). That is, the length L of the through hole 15 is expressed by the following equation:
0.05D ≦ L ≦ 4mm
It was supposed to be set in
図３は、本発明に係る音響管１の第２実施形態と、この音響管１に対して演算部２が接続されて成る音響特性測定装置３を示している。
演算部２はＦＦＴ分析器などで構成されており、音響管１のマイクロフォンからの信号が入力される。演算部２では、ＪＩＳ Ａ 1４０５−２に規定された手法などに基づき、吸音試験材Ｗの吸音率や音響インピーダンスを算出可能となっている。なお、演算部２は、パソコンで構成することも可能であり、その場合、Ａ／Ｄ変換ボードとＦＦＴ分析ソフトが必要となる。
FIG. 3 shows a second embodiment of the acoustic tube 1 according to the present invention and an acoustic characteristic measuring device 3 in which a calculation unit 2 is connected to the acoustic tube 1.
The calculation unit 2 is configured by an FFT analyzer or the like, and receives a signal from the microphone of the acoustic tube 1. The calculation unit 2 can calculate the sound absorption rate and acoustic impedance of the sound absorption test material W based on the method defined in JIS A 1405-2. The calculation unit 2 can also be configured by a personal computer, and in that case, an A / D conversion board and FFT analysis software are required.
以下、本発明に係る音響管１を用いて、ＪＩＳ Ａ １４０５−２に基づき、吸音試験材Ｗの音響インピーダンスを測定した実施例を示す。
使用した音響管は、長さ１５８ｍｍ、内径１６ｍｍ、マイクロフォン中心間距離１５ｍｍ、通孔１５の長さ３．５ｍｍである。
図３は、吸音試験材Ｗを「深さ１０ｍｍの剛壁」とした場合であり、音響インピーダンスを１０ｋＨｚまで測定した結果を示している。
Hereinafter, the Example which measured the acoustic impedance of the sound-absorption test material W based on JISA1405-2 using the acoustic tube 1 which concerns on this invention is shown.
The acoustic tube used has a length of 158 mm, an inner diameter of 16 mm, a microphone center distance of 15 mm, and a length of the through hole 15 of 3.5 mm.
FIG. 3 shows a case where the sound absorption test material W is “a rigid wall having a depth of 10 mm” and the acoustic impedance is measured up to 10 kHz.
この図３においては、伝達マトリックス法による理論値を実線で示し、本発明に係る音響管１を用いて１０ｋＨｚまでの音響インピーダンスを測定した結果を一点鎖線で示し、従来の５ｋＨｚ用音響管（内径３３ｍｍ）を用いて５ｋＨｚまでの音響インピーダンスを測定した結果を破線で示している。また、記号Ｚは音響インピーダンスであり、ρｃは空気の特性インピーダンス（４０８ｋｇ／ｍ2ｓｅｃ）である。 In FIG. 3, the theoretical value by the transfer matrix method is shown by a solid line, and the result of measuring the acoustic impedance up to 10 kHz using the acoustic tube 1 according to the present invention is shown by a one-dot chain line. The results of measuring the acoustic impedance up to 5 kHz using (33 mm) are shown by broken lines. Symbol Z is an acoustic impedance, and ρc is a characteristic impedance of air (408 kg / m 2 sec).
図３から明らかなように、本発明に係る音響管１では、１０ｋＨｚまでの周波数域において理論値と略一致していることが判る。これは音響管１を細くすると共にＭＥＭＳマイクロフォン１７の相互間隔を狭くし、そのうえで管本体５の管壁内面とＭＥＭＳマイクロフォン１７との間に設ける通孔１５を共鳴の起こらない長さＬとしていることにより、５ｋＨｚ以上の高周波数域であっても、音響管１の管軸方向のみに平面波を発生できているためと考察される。 As is clear from FIG. 3, it can be seen that the acoustic tube 1 according to the present invention substantially matches the theoretical value in the frequency range up to 10 kHz. That is, the acoustic tube 1 is made narrow and the mutual interval between the MEMS microphones 17 is narrowed, and the through-hole 15 provided between the tube wall inner surface of the tube main body 5 and the MEMS microphone 17 has a length L that does not cause resonance. Therefore, it is considered that plane waves can be generated only in the tube axis direction of the acoustic tube 1 even in a high frequency range of 5 kHz or more.
これに対し、従来の５ｋＨｚ用音響管では、５ｋＨｚまでは理論値と略一致しているものの、５ｋＨｚを超えると理論値と全く合わなくなっていることが判る。これは５ｋＨｚ用音響管の内径が３３ｍｍであるために、５ｋＨｚを超えた高周波数域では平面波が成立しておらず、またマイクロフォン間隔が長い設定のままであることが原因しているからと考察される。 On the other hand, in the conventional acoustic tube for 5 kHz, it is understood that the theoretical value up to 5 kHz substantially coincides with the theoretical value, but when it exceeds 5 kHz, it does not match the theoretical value at all. This is considered to be because the inner diameter of the acoustic tube for 5 kHz is 33 mm, so that a plane wave is not established in a high frequency region exceeding 5 kHz, and the microphone interval is still set to be long. Is done.
図４は、吸音試験材Ｗを厚み１２ｍｍのフェルト材として、図３と同じ音響管１を用い同条件で音響インピーダンスを１０ｋＨｚまで測定した結果を示している。
図４において、本発明に係る音響管１を用いて１０ｋＨｚまでの音響インピーダンスを測定した結果を実線で示し、従来の５ｋＨｚ用音響管（内径３３ｍｍ）を用いて５ｋＨｚまでの音響インピーダンスを測定した結果を破線で示す。
FIG. 4 shows the result of measuring the acoustic impedance up to 10 kHz under the same conditions using the same acoustic tube 1 as in FIG. 3 using the sound absorption test material W as a felt material having a thickness of 12 mm.
In FIG. 4, the result of measuring the acoustic impedance up to 10 kHz using the acoustic tube 1 according to the present invention is shown by a solid line, and the result of measuring the acoustic impedance up to 5 kHz using the conventional acoustic tube for 5 kHz (inner diameter 33 mm). Is indicated by a broken line.
図４から明らかなように、本発明に係る音響管１では、５ｋＨｚまでの周波数域で従来の音響管とほぼ一致する結果が得られているうえ、５ｋＨｚを超える高周波数域でも、音響インピーダンスを正しく測定できていることが確認できる。
なお、測定下限周波数は、ＪＩＳ Ａ 1４０５−２と同じくマイクロフォン間隔と分析システムの精度に依存する。一般的な指針として、マイクロフォン間隔は波長の５％を上回る必要があり、通常の場合、測定下限周波数は測定上限周波数×０．１程度である。
As is apparent from FIG. 4, the acoustic tube 1 according to the present invention has obtained a result that substantially matches the conventional acoustic tube in the frequency range up to 5 kHz, and has the acoustic impedance even in the high frequency region exceeding 5 kHz. It can be confirmed that the measurement is correct.
Note that the measurement lower limit frequency depends on the microphone interval and the accuracy of the analysis system, as in JIS A 1405-2. As a general guideline, the microphone interval needs to exceed 5% of the wavelength. In a normal case, the measurement lower limit frequency is about the measurement upper limit frequency × 0.1.
ところで、今回開示された実施形態はすべての点で例示であって制限的なものではないと考えられるべきである。特に、今回開示された実施形態において、明示的に開示されていない事項、例えば、動作条件や測定条件、各種パラメータ、構成物の寸法、重量、体積などは、当業者が通常実施する範囲を逸脱するものではなく、通常の当業者であれば、容易に想定することが可能な値を採用している。 By the way, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, such as operating conditions and measurement conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that is normally implemented by those skilled in the art. Instead, values that can be easily assumed by those skilled in the art are employed.
例えば、音響管１において、管本体５は円形管であることに限定されず角形管としてもよい。
また、図５に示されるように、音響管１は、管本体５に対して吸音試験材Ｗを保持する保持部６の背後を延長させて延長管部２０を形成し、この延長管部２０に可動式のピストン２１を設けた構成としてもよい。このピストン２１を管本体５の管軸方向に沿って位置変更させることで、保持部６に保持させる吸音試験材Ｗの「背後空気層長さ」を変更することができ、これによって試験条件を変えられる利点がある。
For example, in the acoustic tube 1, the tube body 5 is not limited to being a circular tube, and may be a square tube.
As shown in FIG. 5, the acoustic tube 1 is formed by extending the back of the holding portion 6 that holds the sound absorption test material W with respect to the tube body 5 to form an extension tube portion 20. Alternatively, a movable piston 21 may be provided. By changing the position of the piston 21 along the pipe axis direction of the pipe body 5, the “back air layer length” of the sound absorption test material W held by the holding portion 6 can be changed, and thereby the test conditions can be changed. There are advantages that can be changed.
１ 音響管
２ 演算部
３ 音響特性測定装置
５ 管本体
６ 保持部
７ 音源部
８ 集音部
１０ スピーカ
１１ ホース
１５ 通孔
１６ 凹部
１７ ＭＥＭＳマイクロフォン
１８ 小孔
２０ 延長管部
２１ ピストン
１００ 音響管
１０１ 管本体
１０２ 保持部
１０３ 音源部
１０４ マイクロフォン
Ｗ 吸音試験材
DESCRIPTION OF SYMBOLS 1 Acoustic tube 2 Calculation part 3 Acoustic characteristic measuring apparatus 5 Tube main body 6 Holding part 7 Sound source part 8 Sound collecting part 10 Speaker 11 Hose 15 Through-hole 16 Recess 17 MEMS microphone 18 Small hole 20 Extension pipe part 21 Piston 100 Acoustic pipe 101 Pipe Main body 102 Holding part 103 Sound source part 104 Microphone W Sound absorption test material
Claims (3)
前記集音部は、前記管本体の管壁を貫通する通孔と、この通孔の管壁外面側の開口周部を拡径するように設けられた凹部と、この凹部に埋め込まれたＭＥＭＳマイクロフォンとを有しており、
前記管本体の管壁内面とＭＥＭＳマイクロフォンとの間を連通する通孔の長さが、当該通孔内で前記音源部から発せられる音波の共鳴を起こす長さよりも短くなるように設定されている
ことを特徴とする音響管。 A holding part for holding the sound absorption test material is provided at one end of the tube main body and a sound source part for generating a sound wave toward the sound absorption test material held by the holding part is provided at the other end of the tube main body, And in the acoustic tube provided with two or more sound collecting units arranged in the tube axis direction on the tube wall between the holding unit and the sound source unit,
The sound collection unit includes a through hole penetrating the tube wall of the tube main body, a recess provided so as to expand an opening peripheral portion of the through hole on the tube wall outer surface side, and a MEMS embedded in the recess. A microphone,
The length of the through hole communicating between the tube wall inner surface of the tube main body and the MEMS microphone is set to be shorter than the length that causes the resonance of the sound wave emitted from the sound source unit in the through hole. An acoustic tube characterized by that.
ｆ＝ｃ／４Ｌb
但し、ｆ：音源部から発せられる音波の最大周波数
ｃ：音速
Acoustic tube according to claim 1, the length of the hole for communicating between said tube wall inner surface and the MEMS microphone, characterized in that there is a shorter dimension than L b which satisfy the following equation.
f = c / 4L b
Where f: maximum frequency of sound wave emitted from the sound source
c: speed of sound
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