JP2005134207A - Sound absorption characteristic measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound absorption characteristic measuring method for measuring easily the sound absorption characteristic of a sound absorbing material. <P>SOLUTION: A sound wave of a super-directive beam acquired by modulating a test signal is radiated to a rigid wall 12 from a parametric speaker 5 for acquiring a sound wave in an audible band by nonlinear interaction in a propagating process in the air as a finite amplitude sound wave which is a strong ultrasonic wave, and the sound waves reflected by the wall 12 in the case where the sound absorbing material 11 is mounted on the wall 12 and in the case where the sound absorbing material 11 is not mounted thereon are collected by a microphone 6 and analyzed by an analyzer 7, to thereby measure the sound absorption characteristic of the sound absorbing material 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sound absorption characteristic measuring method for measuring a sound absorption characteristic of a sound absorbing material.

  A sound absorbing material, which is a sound absorbing material, is generally used in order to take measures against noise that reduces unnecessary sound and to make sound output from a stereo device in a good state. In order to properly use such a sound absorbing material, it is necessary to grasp acoustic characteristics such as a sound absorption coefficient. Conventionally, there are several methods for measuring the sound absorption coefficient such as normal incidence and oblique incidence. For example, there is an acoustic tube method as a general method for measuring the normal incidence sound absorption coefficient.

  FIG. 5 is a diagram showing a configuration of a sound absorption characteristic measurement method by a conventional acoustic tube method defined in Non-Patent Document 1. In this sound absorption characteristic measurement method, a sample 21 to be evaluated is cut out and attached to one end of a circular acoustic tube 20, and the sound source 22 is driven from the other end to measure the sound absorption rate. This method is called a two-microphone method, in which white noise is generated from the sound source 22 in the acoustic tube 20 and the sound pressure level in the tube is measured with the two microphones 23 and 24 arranged in the tube axis direction, and the transfer function is measured. The sound absorption coefficient and acoustic impedance are calculated using the phase difference between the incident wave and the reflected wave. By this method, it is possible to obtain the sound absorption coefficient of the sample 21 on which sound is incident vertically.

  FIG. 6 is a diagram showing a configuration of a sound absorption characteristic measuring method by a conventional reverberation chamber method defined in Non-Patent Document 2. A sample 31 to be evaluated, a sound source 32, and microphones 33 to 36 are installed in a reverberation chamber 30 whose inner surface is almost completely reflective, and sound is collected from the sound source 32 and collected by a plurality of microphones 33 to 36. Make it ready. While the sound from the sound source 32 is stopped and the reverberation time is measured, the oblique incident sound absorption coefficient of the sample 31 is calculated from the difference in the reverberation time measured under the conditions where the sample 31 in the reverberation chamber 30 is present and absent.

  FIG. 7 is a diagram showing an example of the sound absorption coefficient obtained by the reverberation chamber method. The horizontal axis indicates the logarithmic scale frequency, and the vertical axis indicates the sound absorption rate. The sound absorption rate is generally plotted at a frequency of 1/1 or 1/3 octave, and the value is 0 to 1. A general sound-absorbing material, for example, a uniform porous sound-absorbing material such as glass wool, has a low sound absorption rate in the low sound range and a high sound absorption rate in the high sound range, as shown by the characteristic 40 in FIG.

JIS A1405 1998 “Measurement of sound absorption coefficient and impedance by acoustic impedance tube” Japanese Standards Association JIS A1409 1998 “Measurement method of sound absorption rate and reverberation chamber method” Japanese Standards Association

The conventional method for measuring sound absorption characteristics has been carried out as described above, so the acoustic tube method requires time and effort to cut the sample into a precise circle, or a precision acoustic tube, processing software for performance evaluation processing, a personal computer, etc. There was a problem that an expensive system was required.
In addition, the reverberation room method requires a large reverberation room, and there is a problem that expensive dedicated equipment must be prepared.

  The present invention has been made to solve the above problems, and it is possible to easily measure the sound absorption characteristics of the sound absorbing material without requiring an expensive system or expensive dedicated equipment. The purpose is to obtain.

  The sound absorption characteristic measuring method according to the present invention is a super-directive that modulates a test signal from a parametric speaker for obtaining sound waves in the audible band by nonlinear interaction in the process of propagation into the air as finite amplitude sound waves that are powerful ultrasonic waves. The sound absorption of the sound beam is radiated to a rigid wall, and the sound wave reflected by the wall when the sound absorbing material is attached to the wall and without the sound absorbing material is collected and analyzed by a microphone. The sound absorption characteristics of the material are measured.

  The present invention has an effect that by using a parametric speaker for sound absorption characteristic measurement, it is possible to easily measure the sound absorption characteristic of the sound absorbing material without requiring an expensive system or expensive dedicated equipment.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of a sound absorption characteristic measuring method according to Embodiment 1 of the present invention. In FIG. 1, a sound absorbing material 11 as a sample to be evaluated for sound absorption characteristics is attached to a wall 12 having rigidity, and in order to measure the sound absorption characteristics of the sound absorbing material 11, a signal generator 1, an amplitude modulator 2, an amplifier. 3. An electroacoustic transducer 4, a microphone 6 and an analyzer 7 are provided. The amplitude modulator 2, the amplifier 3 and the electroacoustic transducer 4 constitute a parametric speaker 5, and the rigid wall 12 has almost no sound absorption and reflects sound waves almost completely.

  2 is a top view showing the structure of the sound absorption characteristic measuring method shown in FIG. 1, and FIG. 3 is a bird's eye view of the structure of the sound absorption characteristic measuring method shown in FIG. 1, and the same reference numerals as those shown in FIG. is there. The sound wave emitted from the electroacoustic transducer 4 is emitted toward the wall 12, and the sound wave reflected from the sound absorbing material 11 attached to the wall 12 propagates toward the microphone 6 and is collected by the microphone 6.

Next, the operation will be described.
The signal generator 1 generates an audible band test signal, and the amplitude modulator 2 multiplies the ultrasonic carrier signal from a built-in high frequency generator (not shown) and the test signal from the signal generator 1. Amplitude modulation is performed to output a modulated signal. The amplifier 3 amplifies the modulation signal from the amplitude modulator 2 and supplies it to the electroacoustic transducer 4. The electroacoustic transducer 4 converts the modulation signal from the amplifier 3 into a sound wave and radiates it toward the sound absorbing material 11 attached to the wall 12.

  A part of the sound wave (incident wave) incident on the sound absorbing material 11 is absorbed by the sound absorbing material 11 and the rest is reflected. The sound wave (reflected wave) reflected by the sound absorbing material 11 propagates toward the microphone 6. The microphone 6 collects the propagated reflected wave and converts it into an electrical signal, and the analyzer 7 analyzes the electrical signal from the microphone 6 and measures the sound absorption characteristics of the sound absorbing material 3.

  A sound wave radiated from a parametric speaker 5 constituted by the amplitude modulator 2, the amplifier 3 and the electroacoustic transducer 4 causes a nonlinear interaction in the process of propagating into the air as a finite amplitude sound wave which is a powerful ultrasonic wave. Self-demodulated and reproduced as an audible sound wave. The radiated ultrasonic waves and the sound waves in the audible band that are self-demodulated are concentrated on the sound axis that is the central axis of the electroacoustic transducer 4, and have extremely narrow directivity, that is, super directivity. Will have.

  In the first embodiment, the “superdirectivity” property of sound waves emitted from the parametric speaker 5 is used. As shown in FIG. 2, most of the sound waves radiated from the electroacoustic transducer 4 propagate through a thin beam-like area and are reflected like light even after reaching a flat surface such as the wall 12. Since it propagates in the same way, it can be applied to measurement. That is, the sound waves collected by the microphone 6 are mainly reflected sound from the wall 12 while almost no direct sound from the electroacoustic transducer 4 arrives. At this time, the sound absorption characteristics of the sound absorbing material 11 can be measured by evaluating the sound pressure level of the reflected sound when the sound absorbing material 11 is not present on the wall 12.

  When a conventional speaker is used instead of the parametric speaker 5, a high-level direct wave is picked up by the microphone 6, and the emitted sound wave propagates in all directions and is reflected by the wall 12. Since the reflected wave is also collected, it is difficult to collect only the reflected wave from the sound absorbing material 3. Further, in this state, it is impossible to use a continuous stationary sine wave or noise for the test signal, and it is impossible to measure the sound absorption characteristic using the reflected wave in the configuration shown in FIGS. .

Here, the measurement of the sound pressure level when measuring the sound absorption characteristics will be described.
FIG. 4 is a diagram for explaining the measurement of the sound pressure level in the sound absorption characteristic measurement method, FIG. 4 (a) shows the arrangement for measuring the sound pressure level, and FIG. 4 (b) is the electroacoustic conversion that is the sound source. The sound pressure level characteristic with respect to the distance from the device 4 is shown. In general, sound-absorbing characteristics of the sound absorbing material 11 is evaluated by the reflected waves, as shown in FIG. 4 (a), the sound pressure level p _r of the reflected wave and the sound pressure level p _i of the incident wave on the reflective surface become known Can be obtained. In the arrangement of the sound pressure level measurement shown in FIG. 4A, only the reflected wave is measured at the position of the microphone 6, the sound pressure level p _mr when the sound absorbing material 11 is present, and the sound pressure when the sound absorbing material 11 is absent. Level p _mh is obtained.

Further, as shown in FIG. 4B, the reflection surface of the wall 12 exists at a distance of d _h from the electroacoustic transducer 4 (distance = 0), and the total distance from the electroacoustic transducer 4 is folded from there. the microphone 6 is present in the d _m. When there is no sound absorbing material 11, the sound wave is reflected by the wall 12, but as shown by the dotted line of the characteristic 51 in FIG. 4B, the sound pressure level of the reflected wave becomes a characteristic continuous with the sound pressure level of the incident wave. . On the other hand, if there is a sound-absorbing material 11, since the sound absorbing occurs at a distance d _h of the reflective surface, as shown by the solid line characteristic 52 in FIG. 4 (b), the reflected waves from the sound pressure level p _i of the incident wave _Is attenuated to the sound pressure level pr. Here, the sound pressure level difference (p _mh −p _mr ) observed by the microphone 6 is approximately equal to the sound pressure level difference (p _i −p _r ) at the reflecting surface of the wall 12, and is thus measured by the microphone 6. By measuring the sound pressure level p _mh when the sound absorbing material 11 is not present and the sound pressure level p _mr when the sound absorbing material 11 is present, the sound absorption characteristics of the sound absorbing material 11 can be measured.

  The area of the sound-absorbing material 11 as the sample to be evaluated needs to have a certain size, but the area (dimension) is large enough to reach the conical sound wave of the superdirective beam formed by the electroacoustic transducer 4. Is desirable. For example, the distance between the electroacoustic transducer 4 and the wall 12 is about 2 m, and the size of the sound absorbing material 11 is a circular range (−6 dB) in which the sound pressure level in the vertical direction on the central axis of the electroacoustic transducer 4 is halved. ) Or more. The outer peripheral shape of the sound absorbing material 11 may be arbitrary, such as a square shape or a circular shape. Furthermore, it is possible to measure the performance of the sound absorbing material already installed in the building and the sound absorbing ceiling / wall / floor / outer wall / outdoor wall. It becomes.

  The test sound generated by the test signal generated by the signal generator 1 can be a continuous steady sound or a single transient sound. The stationary sound is a sine wave or noise. If it is a sine wave, for example, a 1 kHz single spot sound or a sweep sound whose frequency changes continuously, and if it is noise, white noise, pink noise, 1/1 or 1/3. Band noise such as octave. The transient sound is an impulse or tone burst sound, and by using the transient sound, it can be measured even in a normal room reflected from the periphery of the measurement location. That is, since the propagation path of the super-directional beam emitted from the electroacoustic transducer 4 is limited, the sound wave reflected from the wall 12 or the sound absorbing material 11 is more than the sound wave reflected from the surrounding obstacle or wall. If it reaches quickly, the sound absorption characteristics can be measured. From a developmental point of view, even if continuous sound is used, if the surroundings can be set to an extent that does not affect the reflected sound from other than the reflection path for measurement, the measurement is performed to use the limited super-directional beam. Is possible. On the other hand, it goes without saying that measurement can be performed in an anechoic room or a vast space where no sound waves are reflected.

As an index for measuring the sound absorption characteristic, for example, there is an attenuation amount (p _mh −p _mr ) which is a difference in sound pressure level of reflected sound with the sound absorbing material 11 with respect to the absence of the sound absorbing material 11 (only the wall 12). As described above, this is equal to the sound pressure level difference (p _i −p _r ) between the incident wave and the reflected wave at the reflecting surface of the wall 12. On the other hand, from the sound pressure level p _mh and p _mr measured by the microphone 6, the relationship between the sound pressure level p _r of the reflected wave and the sound pressure level p _i of the incident wave is known, the sound absorption coefficient A is obtained by the following formula be able to.
A = 1- (I _r / I _i )
Here, I _i indicates the intensity of the incident wave, and I _r indicates the intensity of the reflected wave. The intensity I _i of the incident wave and the intensity I _r of the reflected wave can be obtained by the following equations.
I _i = p _i ² / ρc
I _r = p _r ² / ρc
Here, ρ represents the density of air, and c represents the speed of sound. The frequency axis when the measurement index is represented as a graph can take, for example, a discrete value of 1/1 or 1/3 octave, or a continuous value.

  In the configuration of FIGS. 1 to 3, an example in which the incident angle and the reflection angle of the superdirective beam are relatively small is shown, but the angle may be large, and furthermore, a transient sound is used for the test signal. In this case, the electroacoustic transducer 4 and the microphone 6 may be arranged in a straight line (incident angle is 90 degrees = vertical incidence). From this, it is possible to evaluate the sound absorbing material 11 using the incident angle as a parameter, and for example, it is possible to easily obtain a sound absorption coefficient depending on the incident angle.

  As described above, according to the first embodiment, the test signal is obtained from the parametric speaker 5 for obtaining the sound wave in the audible band by the non-linear interaction in the process of propagating in the air as the finite amplitude sound wave that is a strong ultrasonic wave. The sound wave of the super-directional beam modulated with the sound wave is radiated to the rigid wall 12, and the sound wave reflected by the wall 12 when the sound absorbing material 11 is attached to the wall 12 and when there is no sound absorbing material 11 is collected by the microphone. By analyzing, it is possible to easily measure the sound absorption characteristics of the sound absorbing material 11 without requiring an expensive system or expensive dedicated equipment.

  In addition, according to the first embodiment, it is possible to evaluate a sample having a large area as compared with the sound absorption characteristic measurement method using the conventional acoustic tube method, and to measure the sound absorption characteristic in accordance with the actual situation. can get.

It is a block diagram which shows the structure of the sound absorption characteristic measuring method by Embodiment 1 of this invention. It is a top view which shows the structure of the sound absorption characteristic measuring method by Embodiment 1 of this invention. It is a bird's-eye view which shows the structure of the sound-absorption characteristic measuring method by Embodiment 1 of this invention. It is a figure explaining the measurement of the sound pressure level in the sound absorption characteristic measuring method by Embodiment 1 of this invention. It is a figure which shows the structure of the sound absorption characteristic measuring method by the conventional acoustic tube method. It is a figure which shows the structure of the sound absorption characteristic measuring method by the conventional reverberation room method. It is a figure which shows the example of the sound absorption rate calculated | required by the reverberation room method.

Explanation of symbols

  1 signal generator, 2 amplitude modulator, 3 amplifier, 4 electroacoustic transducer, 5 parametric speaker, 6 microphone, 7 analyzer, 11 sound absorbing material, 12 walls.

Claims (4)

  From a parametric speaker to obtain sound waves in the audible band by nonlinear interaction in the process of propagating into the air as finite amplitude sound waves, which are powerful ultrasonic waves, the sound waves of the super-directional beam modulated with the test signal are sent to the rigid wall The sound absorbing characteristic of the sound absorbing material is measured by collecting and analyzing the sound wave emitted and reflected by the wall when the sound absorbing material is attached to the wall and when there is no sound absorbing material. Sound absorption characteristic measurement method.   The sound absorption characteristic of the sound absorbing material is obtained from a difference in sound pressure level of a sound wave reflected by the wall and picked up by a microphone when the sound absorbing material is attached to a wall and when there is no sound absorbing material. The sound absorption characteristic measuring method according to 1.   3. A sound pressure level difference between a sound wave incident on a wall and a sound wave reflected on the wall is obtained from a sound pressure level difference between sound waves picked up by a microphone, and a sound absorption rate of the sound absorbing material is obtained. The sound absorption characteristic measurement method described.   2. The sound absorption characteristic measuring method according to claim 1, wherein a continuous steady sound such as a sine wave or noise or a transient sound such as an impulse or a tone burst is used as the test signal.

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