JP4876287B2 - Measuring method of acoustic impedance and sound absorption coefficient - Google Patents

Description

  The present invention relates to measurement of acoustic impedance and sound absorption coefficient of various samples such as building materials.

  Conventional methods for measuring the sound absorption coefficient and acoustic impedance of a material include a method using a reverberation chamber, a method using an acoustic tube, and a method of measuring on-site in consideration of precise installation conditions between a sound source speaker, a microphone, and a sample. . Hereinafter, conventional methods for measuring sound absorption coefficient and acoustic impedance of materials will be described.

  As a method of using the reverberation chamber, JIS A 1409 and ISO 354 define a method of measuring the reverberation chamber method sound absorption coefficient. This is a method for obtaining the sound absorption rate of a sample by using the Sabine reverberation equation from the reverberation time of the reverberation chamber without the measurement sample and the reverberation time of the reverberation chamber with the measurement sample.

  Further, Patent Document 1 uses the electroacoustic equipment to improve the above measurement method.

FIG. 3 shows one method for measuring the acoustic impedance of a material using an acoustic tube. Install the sample on one side of the acoustic tube and the sound source speaker on the other side. Furthermore, a movable microphone (probe microphone) is installed at the center of the tube. The acoustic impedance of the material is obtained by moving the microphone and measuring the pattern of the standing wave near the material surface, that is, the position where the first P _min occurs.

  FIG. 4 shows a method of measuring the acoustic impedance of a material using an acoustic tube, as described above. Different from the above method, the type of microphone and the installation method are different, and the acoustic impedance of the sample surface is obtained from the transfer function between two points measured by two fixed microphones.

  5 and 6 show a method for measuring the acoustic impedance of a material in the field. The appropriate positional relationship between the sound source / sample / microphone and the type of the sound source are obtained, and the acoustic impedance of the material is obtained based on the conditions.

Patent Document 2 discloses a transfer function between two points measured by two fixed microphones and a plurality of random noises emitted from a speaker or the like when the sound level is insufficient, or when the sound level is insufficient. From this, the acoustic impedance of the sample surface is obtained.
Japanese Patent Laid-Open No. 10-260077 Japanese Patent Laid-Open No. 2003-083805

  The method shown in FIGS. 3 and 4 can determine the sound absorption coefficient of the sample, but cannot determine the acoustic impedance. Furthermore, a large-scale facility such as a reverberation room or a sample of about 10 square meters is necessary, and it is difficult to realize a complete diffuse sound field that is a setting condition of the reverberation room for measurement.

  In the case of the method shown in FIGS. 3 and 4, there is a problem in that the object to be measured is limited to a small sample, and the measured acoustic impedance is different from the characteristics of a sample constructed on the site with a large size.

  The methods shown in FIGS. 5 and 6 are greatly affected by setting conditions such as the characteristics of the sound source and the positional relationship of the sound source / sample / microphone, and the setting and control thereof are complicated. Also, with this method, it is difficult to obtain the material characteristics at a low frequency in a general room.

  In particular, the measurement result is not stable with a material having a low sound absorption coefficient, and it is difficult to perform a proper measurement.

  In the method shown in Patent Document 2, even if a plurality of random noises emitted from a speaker or the like are used when the level of sound existing on the spot is small, an acoustic impedance and a sound absorption coefficient corresponding to the sample cannot be obtained. Or a measurement result changes for every measurement.

  The present invention is intended to solve the problems of the conventional measurement method, and does not require special equipment or large-scale equipment, and can provide stable acoustic impedance and sound absorption coefficient of the material in the construction state. The object is to measure easily and accurately.

Technical means for achieving the object are as follows (1) to (2).
(1) In the vicinity of the object to be measured, two far / near microphones are installed at a predetermined distance, and the sound absorption coefficient of the above material is obtained from a sound source that ensures diffusivity in the two far / near microphones. When the sound pressure level is less than 0.2, the sound pressure level at the near microphone position is 85 dB or more. When the sound pressure level is from 0.2 to less than 0.6, the sound pressure level at the near microphone position is 75 dB or more. A sound having a pressure level of 65 dB or more is incident, a transfer function of the sound pressure between far and near microphones is measured, for example, and the acoustic impedance and sound absorption coefficient of the object to be measured are calculated based on the measured values. Measuring method of impedance and sound absorption coefficient.

(2) When a sound pressure-particle velocity sensor is installed in the vicinity of the object to be measured, and the sound absorption coefficient of the above material is less than 0.2 from a sound source that ensures diffusibility in this sound pressure-particle velocity sensor. When the sound pressure level at the sensor position is 70 dB or more, 0.2 or more and less than 0.6, the sound pressure level at the sensor position is 65 dB or more, and when it is 0.6 or more, the sound pressure level at the sensor position is 55 dB or more. For example, a transfer function between the sound pressure and the particle velocity is measured, and the acoustic impedance and sound absorption coefficient of the object to be measured are calculated based on the measured values.

  The present invention uses an acoustic tube by means of the above features (1) and (2) more easily than when a reverberation chamber is used, including materials with low acoustic absorption and sound absorption coefficient such as building materials. Unlike the case, the difference in each measurement can be stably and accurately measured with the sound absorption coefficient within 0.0015 in the on-site construction state.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the following examples.

1. An example of an embodiment of a method for measuring acoustic impedance of various samples such as building materials according to the feature (1) is shown in FIG. Two far / near microphones 2a and 2b are installed in the vicinity of the DUT 1 at a predetermined distance, and the two far / near microphones are placed at the near microphone position from a sound source that ensures diffusivity. The sound pressure transfer function between the far microphone 1a and the near microphone 1b is measured by a frequency analyzer 3 equipped with a transfer function calculation function, and a sound wave with a sound pressure level of 65 dB or more is entered. The acoustic impedance is calculated from Equation 1, and the sound absorption coefficient is calculated from Equation 2.

ただし、Z_EA(□)：被測定物の表面の音響インピーダンス、H_abEA(□)：二本の遠・近マイクロホン間の伝達関数、□：空気密度、c：空気中の音速、k：波長定数、j：虚数単位、l:二本の遠・近マイクロホン間の距離、d：被測定物表面近マイクロホン間の距離、とする。

Where Z _EA (□): acoustic impedance of the surface of the object to be measured, _HabEA (□): transfer function between two far and near microphones, □: air density, c: speed of sound in air, k: wavelength Constant, j: imaginary unit, l: distance between two far and near microphones, d: distance between microphones near the surface of the object to be measured.

ただし、□_EA(□)：被測定物の吸音率、Z_EA(□)：被測定物の表面の音響インピーダンス、□：空気密度、c：空気中の音速、である。

Where □ _EA (□): sound absorption coefficient of the object to be measured, Z _EA (□): acoustic impedance of the surface of the object to be measured, □: air density, c: speed of sound in the air.

  As a result, a rough sound absorption coefficient can be obtained.

Subsequently, when the above-described rough sound absorption coefficient in the frequency range in which the acoustic impedance or sound absorption coefficient is to be calculated is less than 0.6, when the sound absorption level is less than 0.2, the sound pressure level at the near microphone position is 85 dB or more, 0.2 When the value is less than 0.6, sound waves are output from the sound source so that the sound pressure level at the near microphone position is 75 dB or more. These sound pressure levels are obtained based on experiments performed in the following procedure.

1) First, GW50 is measured as a reference value for evaluating the amount of change for each measurement, and the obtained sound absorption coefficient (hereinafter referred to as Ref.) Is compared with the sound absorption coefficient obtained by measurement under the following six conditions.
Ref. _C1 , Ref. _C2 : Continuously measure with the sound source and measurement points of Ref.
Ref. _R1 , Ref. _R2 : Move the receiving point once and place it again at the same point as Ref.
Ref. _2.5 , Ref. _5.0 : Measure by moving the sound receiving point from the center of the sample by 2.5 and 5.0 [mm] in the long side direction, respectively.

2) Calculate the root mean square of the difference between the sound absorption coefficient obtained under this measurement condition and Ref. For each 1 Oct. band. The result of the method of FIG. 1 is shown in FIG. In all frequency bands, the difference between Ref. _C1 and Ref. _C2 is 0.01 or less, and in the case of Ref. _R1 , Ref. _R2 , Ref. _2.5 and Ref. _5.0 , the difference from Ref is 0.02 or less. Even when the receiving point is moved, the difference in measurement results is small. In addition, the difference of the root mean square of each of the continuous measurement, Ref. _C1 and Ref. _C2 , was within 0.0015.

  3) Next, using the four samples with different sound absorption rates shown in Table 1, the relationship between the measured sound absorption rate and the sound pressure level at the near microphone position is clarified.

The sound pressure level at the near microphone position is increased by 11 steps in 5 dB steps from the sound pressure level shown in Table 2, and the sound pressure level at each step is set to L _{RP_N} (N = 1, 2, ..., 11) Represented by

The change in the sound absorption coefficient measured with respect to the sound pressure level is evaluated by calculating the root mean square D _rms (f _c , N) for each 1 Oct. band using the following equation ( ₃ ).

ただし、nは各bandごとのデータ数、f_{c_k}は中心周波数f_cのk番目の周波数、□( f_{c_k}, N) は音圧レベルL_{RP_N}で測定される、周波数f_{c_k}の吸音率である。

Here, n is the number of data for each band ', k-th frequency f _{c_k} center frequency _{f c, □ (f c_k,} N) is measured by the sound pressure level L _{RP_N,} is sound absorption rate frequency f _{c_k} .

FIG. 8 shows the obtained D _rms (f _c , N) for each sample. From FIG. 8, D _rms (f _c , N) does not change as the sound pressure level increases regardless of the sample and frequency. Further, the porous materials (GW50, GW100, RW25) do not change D _rms (f _c , N) at a lower sound pressure level as the frequency is higher. In CF, D _rms (f _c , N) does not change at approximately the same frequency. The higher the frequency, the higher the sound absorption rate of the porous material, and the CF does not change the sound absorption rate depending on the frequency. Therefore, it is considered that D _rms (f _c , N) does not change at a lower sound pressure level as the sound absorption rate is higher.

With reference to the above 2), the minimum value of the sound pressure level satisfying the following formula 4 is defined as “sound pressure level required for measurement” _LEA .

Fig. 9 shows the relationship between the sound absorption coefficient and _LEA . For each sample, the sound absorption coefficient is an arithmetic average value for each 1 Oct. band, and a straight line regressed by the least square method from the obtained results is also shown. This shows the relationship between the measured sound absorption coefficient and the sound pressure level at the near microphone position.

2. An example of an embodiment of an acoustic impedance measuring method for various samples such as building materials according to the feature (2) is shown in FIG. A sound pressure-particle velocity sensor 4 is installed in the vicinity of the object to be measured. The sound pressure-particle velocity sensor 4 has a sound pressure level that is 55 dB or more at the sensor 4 position from a sound source that ensures diffusibility. Then, the transfer function between the sound pressure and the particle velocity is measured by the frequency analyzer 5 equipped with a transfer function calculation function, and the acoustic impedance of the object to be measured is expressed by the following number based on the measured value. 5, the sound absorption coefficient is calculated according to Equation 2.

ただし、Z_EA(□)：被測定物の表面の音響インピーダンス、H_upEA(□)：音圧−粒子速度間の伝達関数、p(□)：音圧、u(□)：粒子速度、である。

Where Z _EA (□): acoustic impedance of the surface of the object to be measured, _HupEA (□): transfer function between sound pressure and particle velocity, p (□): sound pressure, u (□): particle velocity is there.

  As a result, a rough sound absorption coefficient can be obtained.

Subsequently, when the above rough sound absorption coefficient in the frequency range in which the acoustic impedance or the sound absorption coefficient is to be calculated is less than 0.6, and further less than 0.2, the sound pressure level at the sensor position is 70 dB or more, 0.2 or more and 0. When the sound pressure level is less than 6, a sound wave is output from the sound source so that the sound pressure level at the sensor position is 65 dB or more. These sound pressure levels are obtained based on experiments performed in the following procedure.
This value is based on FIG. 13 obtained by the experiment of the same procedure as 1) to 2) of 1 above.

  In the present invention, as a means for ensuring the diffusibility at the sound receiving point, a plurality of sound sources and moving sound sources or any one of the sound sources is used in the room.

  In the present invention, the test signal may be any signal as long as the frequency to be obtained is included. However, when the measurement is to be performed efficiently, all frequencies are included if pink noise or white noise is used as the test signal.

  In the present invention, one or more measurements are performed or a real-time measurement device is used.

  The speed of material development is possible.

When a sound field is predicted by a computer simulation method, the sound can be accurately predicted by giving the measured sound absorption coefficient or acoustic impedance as the boundary condition of the room, and the sound of the entire room can be controlled.

It is apparatus arrangement explanatory drawing in the Example as described in the said characteristic (1) in this invention. It is apparatus arrangement explanatory drawing in the Example as described in the said characteristic (2) in this invention. It is a figure which shows the standing wave method of one acoustic tube method of a prior art. It is a figure which shows the microphone method of one acoustic tube method of a prior art. It is a figure which shows one reflection method 1 of a prior art. It is a figure which shows one reflection method 2 of a prior art. The graph which shows the comparison of the change of the sound absorption coefficient measured with respect to the sound pressure level between Ref. _C1 , Ref. _C2, Ref. _R1 , Ref. _R2 , Ref. _2.5 , Ref. _5.0 . D _rms (f _c, N) against the four materials with the graph showing the sound pressure level of the relationship in the near microphone position. The graph which shows the relationship between the sound pressure level required for a measurement, and a sound absorption coefficient. The graph which shows the relationship between the sound pressure level required for a measurement, and a sound absorption coefficient.

Explanation of symbols

Claims (2)

Two far / near microphones are installed in the vicinity of the object to be measured at a predetermined distance, and the sound absorption rate of the object to be measured is 0 from the sound source that ensures diffusivity in the two far / near microphones. When the sound pressure level at the near microphone position is 85 dB or more when the sound pressure level is less than 2, the sound pressure level at the near microphone position is 75 dB or more when the sound absorption rate of the object to be measured is 0.2 or more and less than 0.6. A sound wave is incident, and when the sound absorption coefficient of the object to be measured is 0.6 or more, a sound wave having a sound pressure level of 65 dB or more at the near microphone position is incident, and the transfer function of the sound pressure between the far and near microphones is measured. A method for measuring an acoustic impedance and a sound absorption coefficient, wherein the acoustic impedance and the sound absorption coefficient of an object to be measured are calculated based on a measured value. A sound pressure-particle velocity sensor is installed in the vicinity of the object to be measured. When the sound absorption coefficient of the object to be measured is less than 0.2 from the sound source that secures diffusibility in the sound pressure-particle velocity sensor, the sensor A sound wave having a sound pressure level of 70 dB or more is made incident, and a sound wave having a sound pressure level of 65 dB or more is made incident when the sound absorption rate of the object to be measured is 0.2 or more and less than 0.6. When the sound absorption coefficient of the measurement object is 0.6 or more, a sound wave having a sound pressure level of 55 dB or more is made incident on the sensor position, and the transfer function between the sound pressure and the particle velocity is measured. A method for measuring acoustic impedance and sound absorption coefficient, comprising calculating an acoustic impedance and a sound absorption coefficient.

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