JP5876311B2 - Sound absorption coefficient measuring device, sound absorption coefficient measuring method, and sound absorption coefficient measuring program - Google Patents

Description

  The present invention relates to a sound absorption coefficient measuring device, a sound absorption coefficient measuring method, and a sound absorption coefficient measurement program for measuring a sound absorption coefficient of a sample.

As a method for measuring the sound absorption coefficient of a sample, there is a “measurement method of reverberation chamber method sound absorption coefficient” (JIS A 1409: 1998).
The reverberation chamber method sound absorption rate is determined by measuring the reverberation time with and without the sample in the reverberation chamber, and calculating the sound absorption force of the sample from the reverberation time and the volume of the reverberation chamber. The value divided by the horizontal translucent area is the sound absorption coefficient.

By the way, in the measurement of the reverberation chamber method sound absorption coefficient, when the sample area is small, the sound absorption coefficient tends to be measured to be large, and this is particularly noticeable in a material having a high sound absorption coefficient. This phenomenon is known as the “area effect” because the inflow of energy is large at the periphery of the sample due to the difference in sound pressure between the floor surface and the sound absorbing surface, and therefore the sound absorbing force of the sample increases.
By the way, in facilities using sound absorbing materials such as gymnasiums and arenas over a large area, the influence of “area effect” tends to be reduced. When the room acoustic design of such facilities is performed using the reverberation room method sound absorption coefficient that has the effect of “area effect”, the sound absorption force will be excessively estimated, and the predicted value and construction time for the room reverberation time will be estimated. There is a possibility that deviation will occur in the actual measured value later (see, for example, Non-Patent Document 1).

As a result, it is pointed out that the sound absorbing power is insufficient after construction, and there is a possibility that additional construction of the sound absorbing material or the like will occur.
Also proposed are a method for simulating the flow of acoustic energy from the periphery of the sound absorbing material (see Non-Patent Document 2, for example), a method for easily calculating the sound absorption rate of the sound absorbing material at the site where the sound absorbing material is installed, and the like. (For example, refer to Patent Document 1).

JP 2009-236664 A

Koji Oguchi, “Sound absorption characteristics and reverberation time of materials”, Acoustic Technology, Japan Acoustic Materials Association, June 30, 2004, 33 (2), 2-7 Yasuhi Kawai, “Area effect in sound absorption coefficient of reverberation room”, Acoustical Society of Japan, Acoustical Society of Japan, May 1, 2007, 63 (5), 268-274

In Non-Patent Document 2, it is possible to grasp the phenomenon by simulating the flow of acoustic energy from the sound absorbing material periphery, but when designing room acoustics for a facility that uses the sound absorbing material in a large area. However, the calculation of how much sound absorption rate is expected has not been achieved.
Moreover, in the method of calculating the sound absorption coefficient of the sound absorbing material described in Patent Document 1, since the sound absorption coefficient is calculated in an actual site, the sound absorption coefficient without the influence of the “area effect” is predicted. It is difficult to do.
Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and even when it is used for acoustic design of a facility that uses a sound absorbing material in a large area, the accuracy of acoustic design is reduced. An object of the present invention is to provide a sound absorption coefficient measurement device, a sound absorption coefficient measurement method, and a sound absorption coefficient measurement program capable of obtaining a sound absorption coefficient that suppresses noise.

  According to a first aspect of the present invention, there is provided a sound absorption coefficient measuring apparatus comprising: a first measuring device for measuring an acoustic intensity level at a measurement point set at an end position of a sound absorbing material installed in a reverberation chamber; The sound intensity calculation unit for calculating the sound intensity at the end position of the sound absorbing material from the sound intensity level measured by the measuring device, and the sound pressure level in the reverberation chamber at the time of vacancy and when the sound absorbing material is installed, respectively Based on the second measuring device to be measured and the sound pressure level measured by the second measuring device at the time of vacancy and when the sound absorbing material is installed, the acoustic power in the reverberation chamber at the time of vacancy and when the sound absorbing material is installed is calculated. A first acoustic power calculation unit that calculates these differences as acoustic power absorbed by the entire sound absorbing material, and acoustic energy that flows from the sound absorbing material peripheral portion to the sound absorbing material side based on the sound intensity. An inflow acoustic energy prediction unit that predicts the inflow acoustic energy as the inflow acoustic energy, and a second acoustic power that calculates, as the inflow acoustic energy removal acoustic power, the acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material The calculation unit and the equivalent sound absorption area of the entire sound absorbing material are divided by the ratio of the inflow acoustic energy and the inflow sound energy removal sound power to obtain an equivalent sound absorption area corresponding to the inflow sound energy removal sound power, and the inflow And a sound absorption coefficient calculating unit that calculates a value obtained by dividing an equivalent sound absorption area corresponding to acoustic power from which sound energy is removed by the sample area of the sound absorbing material, as a sound absorption coefficient of the sound absorbing material.

The sound absorption coefficient measuring apparatus according to claim 2 is the sound absorption coefficient measuring apparatus according to claim 1, wherein the sound absorbing material is a rectangle, and the measurement point is set at a central portion of each side of the rectangle. It is characterized by.
A sound absorption coefficient measuring apparatus according to a third aspect is the sound absorption coefficient measuring apparatus according to the second aspect, wherein the measurement points are further set at each corner of the sound absorbing material.
According to a fourth aspect of the present invention, there is provided the sound absorption coefficient measuring apparatus according to the third aspect, wherein the first measuring instrument has a direction of 45 degrees with respect to the angle at each measurement point set at each of the angles. And measuring the sound intensity level in the three directions, that is, the direction orthogonal to the side at the position of the end of each of the two sides forming the corner, the measurement point is at each corner of the sound absorbing material. On the other hand, three points are set.

  The sound absorption coefficient measurement apparatus according to claim 5 is the sound absorption coefficient measurement apparatus according to any one of claims 1 to 4, wherein the first measuring device includes a microphone, and the sound absorption material is measured from the surface of the sound absorption material. The microphone is arranged so that a vertical distance to the upper end of the microphone is a position of “10 mm + diameter of the microphone”.

In the sound absorption coefficient measuring method according to claim 6 of the present invention, the sound intensity level of the measurement point including the central four points of each side of the rectangular sound absorbing material installed in the reverberation chamber is measured and measured. The sound intensity at the end position of the sound absorbing material is calculated from the sound intensity level, and based on the sound intensity, the sound energy flowing from the sound absorbing material peripheral portion to the sound absorbing material side is predicted as the inflow sound energy, Measure the sound pressure level in the reverberation room when the room and the sound absorbing material are installed, and calculate the acoustic power in the reverberation room when the sound room is empty and when the sound absorbing material is installed based on the measured sound pressure levels . The difference is defined as the acoustic power absorbed by the entire sound absorbing material, and the acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material is defined as the inflow acoustic energy. The equivalent sound absorption area equivalent to the inflow sound energy removal sound power obtained by dividing the equivalent sound absorption area of the entire sound absorbing material by the ratio of the inflow sound energy and the inflow sound energy removal sound power. Is obtained by dividing the value by the sample area of the sound-absorbing material as the sound-absorbing rate of the sound-absorbing material.

The sound absorption coefficient measurement method according to claim 7 is the sound absorption coefficient measurement method according to claim 6, wherein the inflow acoustic energy is a measurement of the sound intensity, a length of the sound absorbing material, and a preset sound intensity level. It is characterized by the product of height.
Furthermore, a sound absorption coefficient measurement program according to claim 8 of the present invention is an acoustic intensity of a measurement point including four central portions of each side of a rectangular sound absorbing material installed in a reverberation chamber , measured by a sound absorption coefficient measuring device. Obtaining a city level , calculating the sound intensity at the end position of the sound absorbing material from the sound intensity level, and acoustic energy flowing from the sound absorbing material peripheral portion to the sound absorbing material side based on the sound intensity And calculating the sound pressure level in the reverberation chamber at the time of vacancy and when the sound absorbing material is measured, which is measured by the sound absorption coefficient measuring device, and based on the respective sound pressure levels. Calculate the acoustic power in the reverberation room when the room and the sound absorbing material are installed, and calculate the difference between them as the acoustic power absorbed by the entire sound absorbing material. Calculating the acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material as the inflow acoustic energy removing acoustic power, and calculating the equivalent sound absorption area of the entire sound absorbing material as the inflow acoustic energy and the A value obtained by dividing an equivalent sound absorption area equivalent to the inflow sound energy removal acoustic power obtained by proportionality with the ratio of the inflow sound energy removal sound power and further divided by the sample area of the sound absorption material is calculated as the sound absorption rate of the sound absorption material. And a step.

  According to the present invention, the sound power absorbed by the entire sound absorbing material is calculated from the difference between the acoustic power in the room at the time of vacancy and when the sound absorbing material is installed, and the sound intensity of the sound absorbing material is calculated. The acoustic energy flowing into the sound absorbing material from the periphery is predicted as the inflowing acoustic energy, and the inflowing acoustic energy is subtracted from the acoustic power absorbed by the entire sound absorbing material to calculate the acoustic power from which the inflowing acoustic energy is removed. Since the sound absorption coefficient of the sound absorbing material is calculated based on the sound absorption coefficient, the calculated sound absorption coefficient is a sound absorption coefficient that is not affected by the inflow acoustic energy that causes the “area effect”. Therefore, it is possible to easily obtain a sound absorption coefficient in which the influence of the “area effect” is suppressed, and by using the sound absorption coefficient calculated in this way, it is possible to improve the accuracy of acoustic design.

  In particular, when the sound absorbing material is rectangular, the sound absorption rate having a certain degree of accuracy can be calculated by measuring the sound intensity level using the central part of the four sides of the sound absorbing material as a measurement point. The sound intensity level can be calculated by measuring the sound intensity level with the angle of the sound-absorbing material having more remarkable incident direction as the measurement point, and as a result, the accuracy of the sound absorption rate can be improved. Can be improved.

  The first measuring device is a microphone, and is arranged so that the vertical distance from the surface of the sound absorbing material to the upper end of the microphone is a position of “10 mm + radius of the microphone”. Since the first measuring instrument can be easily arranged in the vicinity of a position where the sound intensity level is remarkably high and the sound intensity level in the vicinity of the position where the sound intensity level is remarkably high can be measured, more accurate sound can be obtained. Intensity can be calculated.

It is a lineblock diagram showing an example of a sound absorption coefficient measuring device in one embodiment of the present invention. It is explanatory drawing which shows the detail of the probe for a measurement. It is a figure which shows the function structure of an arithmetic processing unit. It is a flowchart which shows an example of the process sequence of a sound absorption coefficient calculation process. It is a figure showing the measurement point of the sound intensity level LIe. It is a figure for demonstrating the arrangement position of the probe for a measurement. It is a figure for demonstrating the arrangement position of the probe for a measurement. It is an example of the calculation data accompanying the measurement result of sound intensity level LIe, and calculation of sound intensity Ie. It is an example of the calculation data accompanying the measurement result of sound intensity level LIe, and calculation of sound intensity Ie. It is an example of the calculation data accompanying calculation of the acoustic power Pa which the whole sound-absorbing material absorbs. It is an example of the calculation data accompanying calculation of the sound absorption coefficient (alpha) c which is not influenced by the inflow acoustic energy to a sound-absorbing material. It is an example of the calculation data accompanying calculation of the sound absorption coefficient (alpha) c which is not influenced by the inflow acoustic energy to a sound-absorbing material. It is the graph which compared the sound absorption coefficient (alpha) c which is not influenced by inflow acoustic energy, and the reverberation room method sound absorption coefficient (alpha).

Embodiments of the present invention will be described below with reference to the drawings.
<Configuration of Sound Absorption Rate Measuring Device 20>
FIG. 1 is a configuration diagram illustrating an example of a sound absorption coefficient measuring device 20 according to an embodiment of the present invention.
In FIG. 1, 1 is a sound absorbing material as a sample, 2 is a measurement probe as a first measuring device, 3 is a speaker, 4 is a microphone as a second measuring device, 5 is a frequency analyzer, and 6 is a personal computer. An arithmetic processing unit 10 constituted by a reverberation chamber for measuring sound absorption coefficient.
The sound absorbing material 1 is, for example, glass wool having a rectangular shape with a density of 32 kg / m ³ and a thickness of 50 mm. The material and specifications of the sound absorbing material 1 are not limited to this.
The measurement probe 2 is an acoustic intensity probe that conforms to IEC 61043.
Here, the sound intensity is the energy of sound that passes through a unit area per unit time, and is specifically a time-averaged product of sound pressure and particle velocity of air.

For example, as shown in FIG. 2, the measurement probe 2 is configured by providing a spacer 12 between two microphones 11a and 11b having the same characteristics. The microphones 11 a and 11 b are omnidirectional microphones, and output a signal (for example, a voltage signal) corresponding to the measured sound intensity to the frequency analyzer 5.
As the microphones 11a and 11b, those of a general 1/2 inch (diameter 12.7 mm) can be applied. The measurement probe 2 is preferably arranged at a position for measuring the acoustic intensity level LIe at a position of about 10 mm, which is a height from the sample surface at which the acoustic intensity level LIe is significantly increased. It is desirable to arrange so that the distance to the surface is “10 mm + the diameter of the microphone”.
By arranging in this way, the distance between the lower end of the microphone and the sample surface is set to 10 mm, and a desirable height can be almost ensured.

The value of “10 mm” described above is obtained when the sound intensity level LIe is measured at a plurality of points (for example, 16 points) with the vertical distance between the sample surface and the measurement probe being 10 mm and 100 mm. (A sample area is 16.52 m < ² > calculated from the relational expression with the chamber volume prescribed | regulated, for example by JISA1409), and is a numerical value obtained as a value which the acoustic intensity level LIe becomes remarkably high. Even when the acoustic intensity level LIe is measured at an arbitrary point with the distance in the vertical direction between the surface of the sample and the measurement probe being 100 mm to 400 mm at an interval of 100 mm, “10 mm”. An approximate position was obtained as a value at which the sound intensity level LIe was significantly increased.

In the present embodiment, the sound absorbing material 1 installed in the reverberation chamber 10 is measured by the measurement probe 2 at a plurality of measurement points set as shown in FIG.
The speaker 3 generates broadband noise. The speaker 3 is disposed at a corner in the reverberation room 10 or the like.
The microphone 4 is for measuring the sound pressure level in the reverberation room 10 and is disposed, for example, by being attached to a microphone stand or suspended from the ceiling. At this time, the distance between the microphone 4 and the wall of the reverberation room is 1.0 m or more, and the distance between the microphones is ½ or more of the wavelength of the sound of the lowest center frequency to be measured. In the present embodiment, when the sound absorbing material 1 is installed in the reverberation chamber 10 by the microphone 4, that is, the sound pressure level when the sound absorbing material is installed, and when the sound absorbing material 1 is not installed in the reverberation chamber 10, that is, in the empty room. Measure the sound pressure level.

The speaker 3 is a speaker having an omnidirectional radiation pattern, for example, and is disposed at a position defined in JIS A 1409, for example, at two locations separated by at least 3 m or more.
Although one speaker 3 and one microphone 4 are arranged in FIG. 1, a plurality of speakers 3 and microphones 4 are actually arranged.
The frequency analyzer 5 is a device having an acoustic intensity calculation function, which receives the output signals of the microphones 11a and 11b from the measurement probe 2, and based on these, the acoustic intensity for each 1/3 octave band center frequency. The city level LIe (dB) is calculated and stored in the built-in memory.

The frequency analyzer 5 is a device that can measure the sound pressure level (dB), and receives the output signal of each microphone 4, and based on these, the sound pressure level Lp (dB) for each center frequency of each band. Is calculated and stored in the built-in memory.
The arithmetic processing unit 6 inputs the sound intensity level LIe (dB) and the sound pressure level Lp (dB) for each center frequency of each band calculated by the frequency analyzer 5, and the sound flowing into the sound absorbing material 1 based on these. A sound absorption coefficient αc that is not affected by energy is calculated.

FIG. 3 is a diagram illustrating a main functional configuration of the arithmetic processing device 6.
As shown in FIG. 3, the arithmetic processing unit 6 includes an acoustic intensity calculation unit 6a, a first acoustic power calculation unit 6b, an inflow acoustic energy prediction unit 6c, a second acoustic power calculation unit 6d, and a sound absorption unit. A rate calculation unit 6e.
The sound intensity calculation unit 6a calculates the sound intensity Ie at the end position of the sound absorbing material based on the sound intensity level LIe at each measurement point.
The first acoustic power calculation unit 6b calculates the acoustic power Pa absorbed by the entire sound absorbing material from the sound pressure level Lp when the room is empty and when the sound absorbing material is installed.
The inflow acoustic energy predicting unit 6c predicts acoustic energy (inflow acoustic energy) Ee flowing from the sound absorbing material peripheral portion to the sound absorbing material 1 side based on the sound intensity Ie.

The second acoustic power calculation unit 6d calculates the acoustic energy flowing into the sound absorbing material 1 from the difference between the acoustic power Pa absorbed by the entire sound absorbing material and the acoustic energy Ee flowing into the sound absorbing material 1 from the sound absorbing material peripheral portion. Is calculated (acoustic energy-removed acoustic power) Pc.
The sound absorption coefficient calculating unit 6e calculates the sound absorption coefficient αc from which the influence of the acoustic energy flowing into the sound absorbing material 1 is removed based on the acoustic power Pc from which the acoustic energy flowing into the sound absorbing material 1 is removed.

FIG. 4 is a flowchart illustrating an example of a processing procedure of a sound absorption coefficient calculation process for calculating the sound absorption coefficient αc, which is executed by the arithmetic processing device 6.
In the arithmetic processing unit 6, first, as an initial process (step S 1), the sound absorbing material measured according to the sample area S (m ² ), which is a horizontal translucent area of the sound absorbing material 1 as a sample, and JIS A 1409. Information necessary for calculating the sound absorption coefficient αc, such as the entire equivalent sound absorption area A (m ² ), is input.

Next, the process proceeds to step S2, and the sound intensity level LIe (dB) at each measurement point measured at the time of installing the sound absorbing material from the frequency analyzer 5 and the sound pressure level by each microphone 4 at the time of vacancy and at the time of installing the sound absorbing material. Lp (dB) is read.
Next, the process proceeds to step S3, and the sound intensity Ie (W / m ² ) when the sound absorbing material is installed is calculated.

Specifically, first, the average value LIeav of the sound intensity level LIe is calculated based on the sound intensity level LIe at each measurement point measured when the sound absorbing material is installed. For example, based on the sound intensity levels LIe1 to LIen at n measurement points M1 to Mn, the average value LIeav of the sound intensity levels is calculated from the following equation (1). Here, LIeav is an energy average value of LIe as shown in the following formula (1), but may be an arithmetic average value when there is little deviation between the sound intensity levels LIe (dB) at the measurement points.
LIeav
= 10 * log ₁₀ (10 ^{LIen / 10} +10 ^{LIe (n−1) / 10} +... +10 ^{LIen1 / 10} )
...... (1)

The sound intensity at the end position of the sound absorbing material 1 is the energy of sound per unit area and unit time flowing from the sound absorbing material peripheral portion, and the sound intensity level is the sound intensity and the reference sound intensity. It is a logarithmic display of the ratio to Citi. The sound intensity Ie (W / m ² ) at the time of installing the sound absorbing material is calculated from the relational expression shown in the following expression (2).
LIeav = 10 * log ₁₀ (Ie / I ₀ ) (2)
Incidentally, (2) _{I 0} in the formula is a sound intensity of the _reference, which is ^{I 0 = 10 -12 (W /} m 2).

Next, in the process of step S4, the room acoustic power P1 when the room is empty and the room acoustic power P2 when the sound absorbing material is installed are calculated.
Specifically, the room average sound pressure level Lpav is calculated based on the sound pressure levels measured by the plurality of microphones 4. For example, when n microphones 4 are installed and the arrangement positions thereof are M1 to Mn, the room average sound pressure level Lpav is based on the sound pressure levels Lp1 to Lpn at the n measurement points M1 to Mn when the room is empty. Is calculated from the following equation (3).

The room average sound pressure level Lpav is an energy average value of the sound pressure level Lp as shown in the following equation (3), but when the deviation between the sound pressure levels Lp (dB) at the measurement point is small, the arithmetic average It may be a value.
Lpav
= 10 * log ₁₀ (10 ^{Lpn / 10} +10 ^{Lp (n−1) / 10} +... +10 ^{Lp1 / 10} )
...... (3)

Here, the acoustic power level Lw in the room can be considered to be equal to the average sound pressure level Lpav in the room, as shown in the following equation (4). The indoor sound power level Lw (dB) can be expressed by the relational expression shown in the following expression (5).
Lw = Lpav (4)
Lw = 10 * log ₁₀ (P / P ₀ ) (5)
In the equation (5), P is the indoor acoustic power (W), P ₀ is the reference acoustic power (W), and P ₀ = 10 ⁻¹² (W).

Therefore, the indoor acoustic power P (W) can be calculated from the equation (5). That is, it is possible to calculate the acoustic power P1 (W) when the room is empty.
The acoustic power (W) is the energy of sound radiated by the sound source in the room per unit time, and the acoustic power level (dB) is a logarithmic display of the ratio between the acoustic power and the reference acoustic power.

In the same procedure, the room average sound pressure level Lpav is calculated from the equation (3) based on the sound pressure levels Lp1 to Lpn at the n measurement points M1 to Mn when the sound absorbing material is installed. Furthermore, the indoor acoustic power P2 (W) when the sound absorbing material is installed is calculated from the equation (5).
Thus, if the acoustic power P1 at the time of vacancy and the acoustic power P2 at the time of installing the sound absorbing material are calculated, the process proceeds to step S5, and the acoustic power Pa absorbed by the entire sound absorbing material is calculated from the following equation (6). .
Pa = P1-P2 (6)

Next, the process proceeds to step S6, and the acoustic energy Ee flowing from the sound absorbing material peripheral portion to the sound absorbing material side is calculated from the following equation (7).
Ee = Ie × H × L (7)
In the equation (7), Ie is the sound intensity (W / m ² ) at the time of installing the sound absorbing material calculated in the process of step S2. H is the measurement height, and L is the sample peripheral length which is the sum of the lengths of the four sides around the sound absorbing material 1 as the sample.
The measurement height H is the distance between the center of the microphone that measures the sound intensity level LIe and the sample surface.
That is, in the equation (7), the sound intensity passing through the wall-like region along the periphery of the sound absorbing material 1 as a sample, defined by “H × L”, is moved from the sound absorbing material peripheral portion to the sound absorbing material side. The acoustic energy Ee that flows in is used.

Next, the process proceeds to step S7, and the acoustic power Pc from which the acoustic energy flowing from the sound absorbing material peripheral portion is removed is calculated from the following equation (8). In addition, Pa in (8) Formula is the acoustic power which the whole sound-absorbing material calculated from (6) Formula by the process of step S5 absorbs. Ee is the acoustic energy flowing into the sound absorbing material from the sound absorbing material peripheral portion calculated from the expression (7) in the process of step S6.
That is, the acoustic power obtained by removing the acoustic energy flowing from the sound absorbing material peripheral portion is obtained by removing the acoustic energy Ee flowing from the sound absorbing material peripheral portion from the sound power Pa absorbed by the entire sound absorbing material.
Pc = Pa-Ee (8)

Next, the process proceeds to step S8, and the sound absorption coefficient αc from which the influence of the acoustic energy flowing from the sound absorbing material peripheral portion is removed is calculated based on the acoustic power Pc obtained by removing the acoustic energy flowing from the sound absorbing material peripheral portion. calculate.
Specifically, first, based on the acoustic power Pc, the sound absorption force by the sound absorbing material 1 from which the influence of the acoustic energy flowing from the sound absorbing material peripheral portion is removed is calculated. That is, the equivalent sound absorption area A (m ² ) of the entire sound absorbing material 1 is expressed by the acoustic energy Ee flowing from the sound absorbing material peripheral part (the above equation (7)) and the acoustic power Pc (the above equation (8)) from which this is removed. The equivalent sound absorption area Ac divided by the ratio is obtained. That is, it calculates | requires from following Formula (9).
Ac = A × (Pc / (Pc + Ee)) (9)

Next, a value obtained by dividing the obtained equivalent sound absorption area Ac by the sample area S (m ² ), which is the horizontal shadow area of the sound absorbing material 1 as a sample, is calculated as the sound absorption coefficient αc. That is, it calculates | requires from following Formula (10).
αc = Ac / S (10)
Then, the sound absorption coefficient αc obtained by removing the influence of the acoustic energy flowing from the sound absorbing material peripheral portion is displayed. Then, the sound absorption coefficient calculation process ends.
In the sound absorption rate calculation process, each data is calculated for each center frequency of each band, and the sound absorption rate is calculated for each center frequency of each band.

<Overall operation during sound absorption measurement>
Next, the overall operation including the operation of the user and the operation of the sound absorption rate measuring device 20 when measuring the sound absorption rate will be described.
First, the user generates broadband noise from a plurality of speakers 3 in a state where the sound absorbing material 1 is not installed in the reverberation chamber 10, and measures this with n microphones 4. Then, by calculating with the frequency analyzer 5, the sound pressure levels Lp 1 to Lpn at the measurement points M 1 to Mn where the microphones 4 are arranged are calculated and stored in the built-in memory of the frequency analyzer 5.

Next, the sound absorbing material 1 is disposed in the reverberation chamber 10, and in this state, broadband noise is generated from the plurality of speakers 3, and this is measured by n microphones 4, and each measurement point M1 is measured by the frequency analyzer 5. Sound pressure levels Lp <b> 1 to Lpn at ˜Mn are calculated and stored in the built-in memory of the frequency analyzer 5.
In addition, as shown in FIG. 2, the reflective board | plate material 1a for avoiding the incidence | injection of the sound from the side surface of the sound-absorbing material 1 is provided in the perimeter of the side surface of the said sound-absorbing material 1. As shown in FIG.

Next, the sound intensity level is measured at a measurement point set in advance for the sound absorbing material 1 using the measurement probe 2.
For example, as shown in FIG. 5, 16 measurement points in the sound absorbing material 1 are set along the edge of the sound absorbing material 1.
That is, for each side of the rectangular sound-absorbing material 1, a total of four locations are set, one at each central portion, and a total of twelve are set, three at each corner.
Here, it is predicted that the corner portion of the sound-absorbing material 1 has more remarkable diversity in the incident direction of sound compared to the central portion of the side. For this reason, the sound intensity level αc is calculated with higher accuracy by measuring the sound intensity level at each of the corner portions at three locations.

In FIG. 5, the measurement point at the center of a certain side is No1, and each measurement point is No2,.
The measurement probe 2 is arranged so as to be in a direction perpendicular to the side at each measurement point set in this way. For example, as shown in FIG. 6, the relative position between the sound absorbing material 1 and the measurement probe 2 is kept constant by fixing the measurement probe 2 to a support base or the like.

  And in the measurement point of No.1, No5, No9, No13 in the center part of each edge | side of the sound-absorbing material 1, as shown in FIG. 2, the center part of the spacer 12 in the longitudinal direction of the measurement probe 2 is seen from above. It arrange | positions so that the edge part of the sound-absorbing material 1 may become the same position, and arrange | positions so that the longitudinal direction of the probe 2 for a measurement and the side of the sound-absorbing material 1 may orthogonally cross. That is, the microphones 11 a and 11 b are arranged so that one is located on the sound absorbing material 1 side and the other is located on the outside of the sound absorbing material 1 with the end portion of the sound absorbing material 1 interposed therebetween.

  Of the measurement points set at the corners of the sound-absorbing material 1, the measurement points set at the ends of each side, that is, No2, No4, No6, No8, No10, No12, No14, No16, are shown in FIG. As shown in a), when viewed from above, the end of the side where the measurement point is set and the center of the spacer 12 in the longitudinal direction of the measurement probe 2 are in the same position, and the end of the measurement probe 2 However, it arrange | positions so that it may become the same position as the edge part of the other edge | side which makes a corner with the edge | side where the said measurement point was set.

  Further, at the measurement points set at the corners of the sound-absorbing material 1, that is, No3, No7, No11, and No15, as shown in FIG. The two sides forming the corner of the sound absorbing material 1 and the straight line connecting the central portions of the microphones 11a and 11b in the short direction of the measurement probe 2 and the central portion of the spacer 12 in the longitudinal direction of the probe 2 It arrange | positions so that the angle | corner may become 45 degree | times.

Further, the measurement probe 2 is desirably arranged at a position where the acoustic intensity level LIe can be measured at a height of about 10 mm, which is a height from the sample surface where the acoustic intensity level LIe is remarkably high. It is arranged so that the vertical distance to the upper end of is 10 mm + the diameter of the microphone.
Note that, here, a case where measurement is performed while the measurement probe 2 is sequentially moved to each measurement point when measuring the sound pressure level will be described, but the present invention is not limited to this. For example, the measurement may be performed by installing a plurality of measurement probes 2 having the same performance at each measurement point.

When measurement is performed using the measurement probe 2, first, for example, the measurement probe 2 is arranged at the measurement point No1.
Subsequently, broadband noise is generated from the plurality of speakers 3. This is measured with the measurement probe 2, the output signal of the measurement probe 2 is analyzed with the frequency analyzer 5, the sound intensity level LIe (dB) for each center frequency of each band is calculated, and the calculation result is the frequency. The data is stored in a memory built in the analyzer 5.

Next, the measurement probe 2 is moved to the measurement point No2. Then, in the same procedure, the frequency analyzer 5 calculates the sound intensity level LIe (dB) for each frequency and stores it in a predetermined memory. This process is performed for all measurement points, and the sound intensity level LIe (dB) at each measurement point is obtained.
Thus, the measurement operation by the user is completed.

Next, the user causes the arithmetic processing unit 6 to execute the sound absorption coefficient calculation process shown in FIG.
That is, first, the sample area S (m ² ) of the sound absorbing material 1 as a sample and the equivalent sound absorbing area A (m ² ) of the entire sound absorbing material measured in accordance with JIS A 1409 are input (step S1).
In the arithmetic processing unit 6, when these input signals are input, the frequency analyzer 5 subsequently receives the sound intensity level LIe (dB) at each measurement point of the sound absorbing material 1, the vacant room and the sound absorbing material installation time. The sound pressure level Lp (dB) at the measurement points M1 to Mn is read (step S2).

  Then, arithmetic processing is performed in accordance with the processing procedure shown in the flowchart of FIG. 4 to calculate the sound intensity Ie (step S3), to calculate the acoustic power Pa absorbed by the entire sound absorbing material 1 (steps S4 and S5), and around the sound absorbing material The acoustic energy Ee flowing from the part is calculated (step S6), the acoustic power Pc from which the influence of the acoustic energy flowing from the peripheral part of the sound absorbing material is removed is calculated (step S7), and sound absorption is performed based on the acoustic power Pc. The sound absorption coefficient αc is calculated by removing the influence of the acoustic energy flowing from the periphery of the material. Thereby, the sound absorption coefficient calculation process is completed.

Here, as described above, the sound power Pa absorbed by the entire sound absorbing material 1 is calculated from the difference between the sound powers P1 and P2 radiated in the reverberation chamber 10 at the time of vacancy and when the sound absorbing material is installed, and The acoustic energy Ee flowing from the sound absorbing material peripheral portion is calculated, and the acoustic energy Ee flowing from the sound absorbing material peripheral portion is subtracted from the acoustic power Pa absorbed by the entire sound absorbing material 1 to obtain the acoustic energy flowing from the sound absorbing material peripheral portion. The removed sound power Pc is calculated, and the sound absorption coefficient αc is calculated based on the sound power Pc from which the sound energy flowing from the sound absorbing material peripheral portion is removed.
Therefore, the calculated sound absorption coefficient αc is a sound absorption coefficient from which the influence of acoustic energy flowing from the sound absorbing material peripheral portion is removed.

As a result, since the sound absorption coefficient αc is a sound absorption coefficient that is not affected by the acoustic energy flowing from the sound absorbing material peripheral portion, which causes the area effect, the sound absorption material such as a gymnasium or an arena is used by using the sound absorption coefficient αc. By designing the acoustics of a facility used in a large area, the difference between the reverberation time predicted in the acoustic design based on the sound absorption coefficient αc and the reverberation time after facility construction can be suppressed, and the acoustic design is performed with high accuracy. be able to. Therefore, the sound absorption coefficient measuring device 20 can be used as a prediction tool for the sound absorption coefficient αc of the facility.
As a result, since it is less likely that the sound absorption force is excessively expected in the acoustic design stage, it is possible to control the shortage of the sound absorption force after the construction, and it is possible to suppress the occurrence of additional work of the sound absorbing material.

  In addition, as shown in FIG. 5, the sound intensity level measurement points are set not only at the central portion of each side of the rectangular sound absorbing material 1 but also at each corner. The intensity level is measured. Therefore, the sound intensity level is measured by measuring the sound intensity level in a plurality of directions at the corner portion of the sound-absorbing material 1 where the diversity of the sound incident direction is predicted to be more conspicuous than the side center portion. Can be detected more accurately, and as a result, a more accurate sound absorption coefficient αc can be calculated.

<Modification>
In the above embodiment, the sound intensity level LIe and the sound stored in each frequency analyzer 5 are measured after the sound intensity level LIe is measured using the measurement probe 2 and the sound pressure level Lp is measured using the microphone 4. Although the case where the pressure level Lp is read into the arithmetic processing unit 6 and the sound absorption rate calculation process is executed has been described, the present invention is not limited to this.
The result calculated in each frequency analyzer 5 can be configured to be stored on the arithmetic processing unit 6 side.

Further, every time the calculation of the sound intensity level LIe in the frequency analyzer 5 with respect to the output signal of the measurement probe 2 at each measurement point is completed, the calculation result is output to the arithmetic processing unit 6, and at all measurement points. It is good also as a structure which calculates the sound intensity Ie with the arithmetic processing unit 6 at the time of the sound intensity level LIe being input.
Similarly, every time the calculation of the sound pressure level Lp in the frequency analyzer 5 with respect to the output signal of each microphone 4 is completed, the calculation result is output to the arithmetic processing unit 6 and the sound pressure levels Lp corresponding to all the microphones 4 are output. It is also possible to have a configuration in which the sound power Pa is calculated in the arithmetic processing unit 6 and the sound absorption coefficient αc is calculated based on this.

Moreover, although the case where 16 points | pieces were set as a measurement point was demonstrated in the said embodiment, it does not restrict to this.
For example, only the central part of each side of the rectangular sound-absorbing material 1, that is, only four points of measurement points No1, No5, No9, and No13 in FIG. 5 may be measured. For example, in a room with a uniform sound pressure distribution, such as a reverberation room, variation in measurement results at each measurement point is small. In such a case, only four measurement points may be measured simply.
In this way, by setting the number of measurement points to four, the time required for measurement and the processing time required for calculating the sound absorption coefficient αc can be reduced accordingly.

Examples of the present invention will be described below. In addition, this invention is not limited to this Example.
As a sample, the sample area was obtained from the calculation formula for the chamber volume defined in JIS A 1409, 16.52 (m ² ) (sample peripheral length 16.36 m) (in JIS A 1409, the chamber volume was 250 m ³ In the case of larger than the above, the sound absorption coefficient αc was measured using the sound absorbing material 1 which is a required sample area determined by the calculation formula for the chamber volume.

The sound intensity is divided into two cases: when all 16 points shown in FIG. 5 are used as measurement points, and when only four central points (No1, No5, No9, No13) shown in FIG. 5 are used as measurement points. The city level was measured. However, in the measurement environment in which the main measurement was performed, measurement was performed at 15 measurement points because there was a position (No 3) where the installation of the measurement probe 2 was difficult.
As the measurement probe 2, the microphones 11a and 11b having a diameter of 1/2 inch (12.7 mm) were used.
In addition, the sound pressure level Lp was measured at the measurement points M1 to M5 using five microphones 4.

8 to 13 show data used for calculating the sound absorption coefficient αc of the sample and various data obtained in the calculation process for each 1/3 octave band center frequency.
FIG. 8 shows acoustic intensity levels LIe (dB) at 15 measurement points excluding No. 3 shown in FIG. 5, LIeav (dB), which is an average value of acoustic intensity levels LIe (dB), and acoustic intensity Ie ( W / m ² ) for each 1/3 octave band center frequency.

  From FIG. 8, the value of the measurement point (No2-No4, No6-No8, No10-No12, No14-No16) of the corner part of the sound-absorbing material 1 is the measurement point (No1, No5, It can be seen that the deviation between the measured values at the same 1/3 octave band center frequency is larger than the values of No9 and No13). That is, for example, when the 1/3 octave band center frequency is 100 Hz, the sound intensity level LIE (dB) is “81.9” at the measurement points (No 1, No 5, No 9, No 13) at the center of the four sides of the sound absorbing material 1. The sound intensity level LIE (dB) is measured at the measurement points (No2 to No4, No6 to No8, No10 to No12, No14 to No16) at the corners of the sound absorbing material 1 while being in the range of ˜83.5 ”. It is over the range of “74.8-93.9”, and it can be seen that the deviation between the measured values is large.

FIG. 9 shows the average value of the sound intensity level LIe (dB) and the sound intensity level LIe (dB) at the four measurement points (No1, No5, No9, No13) shown in FIG. ) And sound intensity Ie (W / m ² ).
FIG. 10 shows acoustic power Pa (W) absorbed by the entire sound absorbing material, various data at the time of vacancy used for calculation of the acoustic power Pa, and various data at the time of installing the sound absorbing material. In FIG. 10, as various data, acoustic power P1 (W) or P2 (W), indoor acoustic power level Lw (dB), indoor average sound pressure level Lpav (dB), and sound pressure level Lp1 at measurement points M1 to M5. ~ Lp5 is shown.

11 and 12 show various data used in calculating the sound absorption coefficient αc using the acoustic energy Ee flowing from the sound absorbing material peripheral part. FIG. 11 shows 15 measurement points. In the case of “15 measurement numbers”, FIG. 12 shows the case of “measurement number 4” with 4 points as measurement points.
11 and 12, as various data, the sound intensity Ie (W / m ² ), the sound energy Ee (W) flowing from the sound absorbing material peripheral portion, and the sound power Pa (W) absorbed by the entire sound absorbing material. And the influence of the acoustic power Pc (W) from which the acoustic energy flowing from the sound absorbing material peripheral portion is removed, the equivalent sound absorbing area A (m ² ) of the entire sound absorbing material, and the acoustic energy flowing from the sound absorbing material peripheral portion are removed. An equivalent sound absorption area Ac (m ² ), a sound absorption coefficient αc from which the influence of acoustic energy flowing from the periphery of the sound absorption material is removed, an actual measurement value α of the reverberation chamber method sound absorption coefficient measured in accordance with JIS A 1409, Is shown. Here, the calculation was performed with the measurement height H set to H = 16.3 mm.

FIG. 13 is a graph comparing the sound absorption rate αc at “measurement number 15” shown in FIG. 11, the sound absorption rate αc at “measurement number 4” shown in FIG. 12, and the actual measurement value α of the reverberation chamber method sound absorption rate. The horizontal axis represents the 1/3 octave band center frequency, and the vertical axis represents the sound absorption coefficient.
It can be seen that the sound absorption coefficient αc when the measurement point is “measurement number 15” and the sound absorption coefficient αc when the measurement point is “measurement number 4” show substantially the same value. Therefore, in a room with a uniform sound pressure distribution, such as a reverberation room, the sound absorption rate is calculated with 4 measurement points, without calculating the sound absorption rate with 15 measurement points. It is possible to acquire a sound absorption coefficient having the same accuracy as the calculated case, that is, it is possible to acquire an accurate sound absorption coefficient in a shorter time.

  Further, as shown in FIG. 13, by showing an actual measurement value α of the reverberation room method sound absorption coefficient that is affected by the area effect and a sound absorption coefficient αc that is not affected by the area effect, the actual measurement value α and the sound absorption coefficient αc. When designing room acoustics for facilities that use sound absorbing materials in large areas such as gymnasiums and arenas, it is easy to determine how much sound absorption rate is expected, that is, how much sound absorption rate is corrected from the measured value α I can know.

DESCRIPTION OF SYMBOLS 1 Sound absorption material 2 Probe for measurement 3 Speaker 4 Microphone 5 Frequency analyzer 6 Arithmetic processing device 10 Reverberation chamber 20 Sound absorption rate measuring device

Claims (8)

A first measuring device for measuring the sound intensity level of the measurement point set at the end position of the sound absorbing material installed in the reverberation chamber;
An acoustic intensity calculation unit for calculating an acoustic intensity at an end position of the sound absorbing material from the acoustic intensity level measured by the first measuring device;
A second measuring device for measuring the sound pressure level in the reverberation chamber at the time of vacancy and when the sound absorbing material is installed;
Based on the sound pressure level at the time of vacancy and at the time of installing the sound absorbing material measured by the second measuring device, the acoustic power in the reverberation room at the time of vacant and at the time of installing the sound absorbing material is calculated, A first sound power calculation unit that calculates the sound power to be absorbed;
Based on the sound intensity, an inflow acoustic energy predicting unit that predicts acoustic energy flowing from the sound absorbing material peripheral portion to the sound absorbing material side as inflow acoustic energy;
A second acoustic power calculation unit that calculates the acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material, as the inflow acoustic energy removal acoustic power;
The equivalent sound absorption area of the entire sound absorbing material is prorated by the ratio of the inflow acoustic energy and the inflow sound energy removal sound power to obtain an equivalent sound absorption area corresponding to the inflow sound energy removal sound power, and the inflow sound energy removal sound is obtained. A sound absorption coefficient calculating unit that calculates a value obtained by dividing an equivalent sound absorption area equivalent to power by a sample area of the sound absorbing material, as a sound absorption coefficient of the sound absorbing material;
A sound absorption coefficient measuring device comprising:   The sound absorption coefficient measuring apparatus according to claim 1, wherein the sound absorbing material is rectangular, and the measurement point is set at a central portion of each side of the rectangle.   The sound absorption coefficient measuring device according to claim 2, wherein the measurement point is further set at each corner of the sound absorbing material.   At each measurement point set at each corner, the first measuring device is orthogonal to the side at a direction of 45 degrees with respect to the corner and at the end of each of the two sides forming the corner. 4. The sound absorption coefficient measurement according to claim 3, wherein three measurement points are set for each angle of the sound absorbing material by measuring sound intensity levels in three directions. apparatus.   The first measuring device includes a microphone, and is arranged such that a vertical distance from the surface of the sound absorbing material to the upper end of the microphone is a position of “10 mm + diameter of the microphone”. The sound absorption rate measuring device according to any one of claims 1 to 4. The acoustic intensity level of the measurement point including the central four points of each side of the rectangular sound absorbing material installed in the reverberation chamber is measured, and the sound intensity at the end position of the sound absorbing material is measured from the measured sound intensity level. To calculate
Based on the sound intensity, predicting the acoustic energy flowing from the sound absorbing material peripheral part to the sound absorbing material side as inflow acoustic energy,
Measure the sound pressure level in the reverberation chamber at the time of vacancy and when installing the sound absorbing material, calculate the acoustic power in the reverberation chamber at the time of vacancy and when installing the sound absorbing material based on the measured sound pressure level , Is the acoustic power absorbed by the entire sound-absorbing material,
The acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material is calculated as the inflow acoustic energy removal acoustic power,
An equivalent sound absorption area corresponding to the inflow sound energy removal acoustic power obtained by dividing the equivalent sound absorption area of the entire sound absorption material by a ratio of the inflow sound energy and the inflow sound energy removal sound power, and a sample of the sound absorption material A sound absorption coefficient measuring method, wherein a value obtained by dividing by an area is used as the sound absorption coefficient of the sound absorbing material.   7. The sound absorption coefficient measuring method according to claim 6, wherein the inflow acoustic energy is a product of the sound intensity, a length of the sound absorbing material and a predetermined measurement height of the sound intensity level. Obtaining the sound intensity level of the measurement point including the central four points of each side of the rectangular sound absorbing material installed in the reverberation chamber , measured by the sound absorption coefficient measuring device, and obtaining the sound absorbing material from the sound intensity level. Calculating the sound intensity at the end position;
Predicting acoustic energy flowing into the sound absorbing material from the sound absorbing material peripheral portion as inflow acoustic energy based on the sound intensity; and
Obtaining the sound pressure level in the reverberation chamber at the time of vacancy and when the sound absorbing material is installed , measured by the sound absorption coefficient measuring device, and based on the respective sound pressure levels , the reverberation chamber at the time of vacancy and when installing the sound absorbing material Calculating the acoustic power of each, and calculating the difference between these as the acoustic power absorbed by the entire sound absorbing material,
Calculating the acoustic power obtained by removing the inflow acoustic energy from the acoustic power absorbed by the entire sound absorbing material as the inflow acoustic energy removing acoustic power;
An equivalent sound absorption area corresponding to the inflow sound energy removal acoustic power obtained by dividing the equivalent sound absorption area of the entire sound absorption material by a ratio of the inflow sound energy and the inflow sound energy removal sound power, and a sample of the sound absorption material Calculating the value divided by the area as the sound absorption rate of the sound absorbing material;
A sound absorption coefficient measurement program executed in a computer of the sound absorption coefficient measurement apparatus .

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