JPH10260077A - Acoustic characteristic measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple device for measuring an acoustic characteristic with a high degree of accuracy. SOLUTION: A reverberation chamber 10 incorporates a sample 12 having a acoustic absorptivity to be measured, and microphones 20, 22, 24 and speakers 14, 16, 18. A sound source signal 27 for measurement delivered from a sound source waveform generating circuit 26 is issued from the speakers 14, 16, 18, and are diffused by an electroacoustic feed-back loop 100 which is a signal path change-over circuit 80 for changing over signal paths 94, 96, 98 in time so as the aim at spatially averaging the acoustic feed-back. Further, the electrocoustic feed-bask loop 100 is average in a frequency range by time- variably type FIR filters 82, 84, 86 having parameters which are changed sometimes. With these averaging operations, the sound field diffusion in the reverberation chamber 10 is improved greatly. A signal during a damping process in the electroacoustic feed-back loop 100 is fed to a level recorder 43 for recording therein a reverberation sound waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring sound characteristics such as sound absorbing properties of sound absorbing material and sound pressure characteristics of equipment such as speakers and air conditioners in a measuring room such as a reverberation room. With this configuration, high-accuracy acoustic characteristic measurement can be performed.

[0002]

2. Description of the Related Art The measurement of sound absorption characteristics (such as sound absorption coefficient) of a sound absorbing material or the like and sound pressure characteristics (power level such as noise power) of equipment such as a speaker and an air conditioner is usually performed using a reverberation room. FIG. 2 shows a system configuration of a conventional sound absorption coefficient measuring device. In a reverberation room 10 (shown in a plan view), a sample 12 to be measured (a sound absorbing material or the like) is arranged. A plurality of speakers 14, 16, 18 are arranged around the sample 12, and a plurality of microphones 20, 22, 24 are arranged at appropriate places.

[0003] The measurement of the reverberation time is required for the measurement of the sound absorption coefficient. The measurement configuration of the reverberation time is as follows. From the sound source waveform generation circuit 26, for example, an impulse,
A sound source signal 27 for measuring short sound (filtered impulse) or band noise is output, and the switch SW
1, SW2, SW3 contact 1 and power amplifier 28,
The loudspeakers 14, 16, 18 utter voices via the speakers 30, 32. The microphones 20, 22, and 24 collect the sound radiated into the reverberation room 10. The picked up signal is head amplifier 3
4, 36, 38, a root mean squarer 40 obtains a root mean square, a root mean square analyzer 42 obtains a spatial set average of the reverberation waveform, or a reverberation waveform is recorded in a level recorder 43 or the like. The sound absorption characteristics are determined based on the measured values.

FIG. 3 shows a system configuration of a conventional power level measuring device such as a speaker (a portion for performing sound absorption correction is omitted). A speaker 44 to be measured is arranged in the reverberation room 10. In addition, a plurality of microphones 46, 48, and 50 are arranged at appropriate locations in the reverberation room 10. The measurement of the sound pressure level is required for the measurement of the power level. The measurement configuration of the sound pressure level is as follows. A sound source signal 53 for measurement is output from a sound source waveform generating circuit 52 and is uttered from a speaker 44 via a power amplifier 54. The microphones 46, 48, and 50 collect the sound radiated into the reverberation room 10. The picked-up signal is root-mean-squared by a root-mean-squaring device 64 via head amplifiers 56, 58, 60 and a band-pass filter 62.
6 shows the output (sound pressure level) for each band. The power level can be obtained by correcting the obtained sound pressure level with a separately measured sound absorption power (measured by the same method as the sound absorption coefficient measurement).

In the measurement of sound absorption characteristics such as sound absorption coefficient, sound field diffusion in the reverberation decay process affects sound accuracy, and in sound pressure characteristics such as power level, sound field diffusion in a steady state affects measurement accuracy. For this reason, in various measurement standards (such as ISO), various conditions are set for the shape and size of the reverberation chamber itself, and the rotating diffuser 6 is provided in the reverberation chamber 10 as shown in FIG.
8 (mainly contributes to the improvement of the diffusion in the attenuation process), and fixed diffusers 70, 72 and 74 are installed in the reverberation chamber 10 as shown in FIG. It contributes to the improvement of steady-state diffusion.)

[0006]

When a diffusion plate is used as shown in FIG. 4, there is a disadvantage that the apparatus becomes large and the installation cost increases. In particular, when trying to obtain a diffusion improvement effect even in the low frequency range, there was a tendency that both the size and the weight were increased. In addition, the effect of improving the diffusion is small. Especially in the case of a fixed diffusion plate, there is no method for deciding the optimum arrangement, and a very large number of cuts and tries have been forced. Further, the diffusion plate tends to press down the installation space of the material to be measured (sound absorbing material, machine under test, speaker, etc.).

SUMMARY OF THE INVENTION The present invention aims to provide an acoustic characteristic measuring device which solves the drawbacks of the conventional technique and realizes a sound field diffusion with a simple device so that highly accurate acoustic characteristic measurement can be performed. It is.

[0008]

SUMMARY OF THE INVENTION The present invention basically provides
A plurality of microphones arranged in the measurement room; a plurality of speakers arranged in the measurement room; and a plurality of signal paths for supplying sound pickup signals from the plurality of microphones to the plurality of speakers. And an electroacoustic feedback loop constituting an acoustic feedback path through which the sound uttered by the microphone is acoustically returned to the plurality of microphones, and the plurality of microphones on a plurality of independent signal paths from the plurality of microphones to the plurality of speakers. Signal path switching means for temporally switching the connection relationship between the plurality of speakers to spatially average acoustic feedback,
By disposing electric transfer characteristic changing means arranged in the signal paths of the plurality of systems to change each electric transfer characteristic over time to average in a frequency domain of the acoustic feedback signal, The acoustic characteristic is measured while improving the sound field diffusion characteristic in the measurement room.

[0009] Claims 2 to 4 are configurations for measuring reverberation characteristics in order to obtain sound absorption characteristics such as sound absorption coefficient and sound absorption power as acoustic characteristics measurement. Claims 5 and 6 are claims as acoustic characteristics. This is a configuration for measuring a sound pressure level in order to obtain a sound pressure characteristic such as a power level of a sound source.

According to the present invention, an electro-acoustic feedback loop is formed between a plurality of speakers and a plurality of microphones, and spatial averaging of acoustic feedback is achieved by switching control of a signal path by signal switching means, and electrical transmission is performed. Averaging in the frequency domain of the acoustic feedback signal is achieved by the characteristic changing means. Therefore, the acoustic characteristics are measured in a state where the sound field in the measurement room is sufficiently diffused, so that the acoustic characteristics can be measured with high accuracy. Further, the sound field can be diffused without using a diffusion plate, and can be realized with a simple configuration.

When measuring sound absorption characteristics such as sound absorption coefficient and sound absorption force as acoustic characteristics measurement, a sample, a measurement speaker and a measurement microphone are arranged in a reverberation room, and a measurement sound source is uttered from the measurement speaker. The reverberation time is measured by measuring the decay process of the signal picked up by the measuring microphone after the sound of the measuring sound source is finished, and the sound absorption characteristics such as the sound absorption coefficient and the sound absorbing power of the sample are determined based on the reverberation time. be able to. In this case, the speaker or microphone for measuring the sound absorption characteristics can be used also as the speaker or microphone constituting the electroacoustic feedback loop, and the configuration can be further simplified.

When measuring sound pressure characteristics, a sound source to be measured (e.g., a machine or a speaker under test) and a measurement microphone are arranged in a reverberation chamber, and the sound to be measured is uttered from the sound source. At this time, the sound pressure level characteristic can be obtained by analyzing the signal collected by the measurement microphone and measuring the output level for each frequency band. Further, by separately measuring the reverberation time of the measurement room in the same manner as the measurement of the sound absorption characteristics, to determine the sound absorption of the measurement room based on this, by correcting the determined sound pressure level with the sound absorption,
The sound pressure characteristic of the sound uttered from the sound source can be measured. In this case, the microphone for measuring sound pressure characteristics is used not only as a microphone constituting the electroacoustic feedback loop but also as a microphone for measuring reverberation time for sound absorption correction. Can be further simplified.

By the way, the switching speed of the signal path by the signal path switching means can be determined as follows. Now
Considering the case of sound absorption characteristic measurement, the lower limit of the switching speed is determined by the reverberation waveform observation range (-5 dB to -3 dB) used for normal measurement.
5 dB), almost half of the reverberation time, ie, T ₆₀
/ 2, it is determined on the condition that the number of switching times N can obtain a sufficient diffusion state. Number of switching N to obtain sufficient diffusion
Is about 20 times at the minimum, and when T ₆₀ = 5 seconds, the lower limit value f ₁ (Hz) of the switching speed is f ₁ = 20 / (5/2) = 8 Hz. In practice, spatial averaging at about 10 points (average in the squared sound pressure area) is performed, so it may be much lower than this.
A sufficient diffusion state can be obtained in the attenuation process of the sound absorption characteristic measurement at about 10 ^−1/2 (since the fluctuation becomes n ^−1/2 by averaging at n points), that is, at about f ₁ = 3 Hz.

On the other hand, the upper limit value f ₂ (Hz) of the switching speed is not equal to the frequency f _{car of the} measurement band, that is, the condition that the interference such as a beat does not occur between f _car and f ₂ is provided. For example, about f _car / 3 is considered to be the upper limit. ISO
And the like, the reverberation chamber volume is defined as 150 to 200 m ³ on the assumption that a sufficient number of modes are secured in the observation band and measurement is performed in a band of 125 Hz or more. That is, in the case of 1/1 oct., A 125 Hz band is generally used. Therefore, f _car = 100 Hz is appropriate, and f ₂ = f _car / 3, that is, the upper limit f ₂ is approximately 30 (Hz). From the above, the switching speed of the signal path by the signal switching means is 3 Hz to 3 Hz.
0 Hz is considered reasonable.

When a plurality of electro-acoustic feedback loops are provided and the time is switched over for the purpose of supporting a sound field for music use in a hall or the like, the reproduced sound is a sound for human viewing. For this reason, the switching speed as described above causes a sense of incongruity and cannot be used (preferably 2 Hz or less). However, in the measurement of acoustic characteristics, since there is no such a restriction related to the perception, there is no such limitation. Even a switching cycle of 30 Hz can be used.

If a band-pass filter that passes only a band matching the measurement band is inserted in each signal path constituting the electro-acoustic feedback loop, even if the switching speed is higher than 30 Hz, the signal is generated due to beat interference or the like. The spectrum component of the sideband can be cut from the loop. Therefore, in that case, the upper limit of the switching speed is higher than 30 Hz.

The switching speed in the measurement of the sound pressure characteristic can be set to be equal to the switching speed in the measurement of the sound absorption characteristic. However, the measurement of the sound pressure characteristic measures the sound whose sound source is uttered steadily. Therefore, there is no requirement for quick switching in a short time, and if the time constant of the effective value circuit for measuring the output level is made sufficiently large, the lower limit of the switching speed can be made lower than 3 Hz.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of sound absorption coefficient measurement according to the present invention is shown in FIG. The same parts as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, the speaker and the microphone constituting the electroacoustic feedback loop are also used as the measurement speaker and the microphone. The sound absorption coefficient measuring device 76 is a device for obtaining a sound absorption coefficient by a reverberation room method, and a sample 12 (a sound absorbing material or the like) to be measured is disposed in the reverberation room 10 (shown in a plan view). A plurality of speakers 1 are provided around the sample 12.
4, 16, 18 are arranged, and a plurality of microphones 20, 22, 24 are arranged at appropriate places.

A sound source signal 27 for measurement, such as band noise and filtered impulse, is output from the sound source waveform generating circuit 26 in a non-correlated manner in each system.
The speaker 14, 16, 18 produces a sound via the contact 1 of the switch SW 3 and the power amplifiers 28, 30, 32. The microphones 20, 22, and 24 collect the sound radiated into the reverberation room 10. The picked-up signals are output to the head amplifiers 34, 36, 38
Is averaged by a root-mean-square unit 40 through a square-meaning unit 40, R. The spatial set average of the reverberation waveform is calculated based on Schroeder's impulse response square integration method, and the reverberation waveform is recorded in the level recorder 43 or the like (when the steady band noise method is used, the reverberation waveform is recorded for each measurement band). T), sound absorption characteristics are required based on this.

The input signal to the root-mean-square unit 40 may be taken from any place as long as it is on a closed loop. In addition to the configuration shown in FIG.
It can be configured to take out from each contact 2 of W2 and SW3.

The outputs of the head amplifiers 34, 36 and 38 are A
It is input to an FC (Active Field Control) function unit 78. The AFC function unit 78 includes a signal path switching circuit 80, time-varying FIR filters 82, 84, 86, and equalizers 88, 9
0,92. The signal switching circuit 80 repeatedly switches the three signal paths 94, 96, and 98 sequentially and temporally.

Signal path 9 by signal path switching circuit 80
An example of the switching operation of 4, 96, 98 is shown in FIG. The signal path switching circuit 80 forms a kind of level matrix,
The input signals of the systems are equally distributed to the outputs 1 to 3 of the three systems at a constant cycle while being alternately replaced. To keep the sum of the gains of the three systems constant at each time point,
The gain changes continuously according to, for example, a sine curve or a triangular wave, or independent random signals satisfying the above conditions. According to this, three microphones 20, 2
The same effect is obtained as when the positions 2, 24 are repeatedly and alternately switched between their installation positions, and the transfer characteristics are flattened by spatial averaging. The switching cycle is set to, for example, about 1/30 sec to 1/3 sec (3 Hz to 30 Hz).

The output signals of the three systems output from the outputs 1 to 3 of the signal path switching circuit 80 are supplied to the time-varying FIR filter 8.
2, 84 and 86 to generate reflected sound signals. The reflected sound parameters of the time-varying FIR filters 82, 84, 86 are set to mutually different parameters, and individually and continuously and randomly on the time axis as shown in FIG. Is changed to Thereby, the time-varying FIR filters 82, 84, 8
Disturbance of the frequency characteristics that occurs when 6 is a fixed type is reduced, and the frequency characteristics are greatly averaged. In addition, the fluctuation of the time axis of the parameter is within a range where the spectrum of the sideband wave due to the fluctuation does not exceed the measurement band (for example, 0.25 msec to
Time-varying FIR filters 82 and 8 (with a fluctuation range of 5 msec)
This is realized by moving the 4,86 output taps uncorrelated.

Signals output from the time-varying FIR filters 82, 84, 86 are input to equalizers 88, 90, 92, and are subjected to frequency characteristics due to the room to be used and the installation locations of the speakers 14, 16, 18 and the like. To roughly flatten the inherent swell of. The characteristics of the equalizers 88, 90, and 92 are automatically or manually adjusted for each frequency band so that the peak on the loop gain of each system becomes -12 dB with respect to the howling point.
If 0, 92 is used as a band-pass filter that passes only the band that matches the measurement band, even if the switching cycle of the signal switching circuit 80 is set higher than the above-described 30 Hz, the spectral component of the sideband generated due to beat interference or the like is reduced. It is cut off from the loop, so that adverse effects on the measurement result can be rationally avoided. Further, as a band-pass filter for the same purpose, it is also possible to insert a band-pass filter 62 in FIG. 9 described later.

The signals output from the equalizers 88, 90 and 92 are supplied to the contacts 2 of the switches SW1, SW2 and SW3. As described above, the sound uttered from the speakers 14, 16, 18 is acoustically returned to the microphones 20, 22, 24, and further passes through the signal paths 94, 96, 98 to reach the speakers 14, 16, 18 again. Independent electroacoustic feedback loop 100 (ie, independent signal paths)
Is configured.

The method of measuring the sound absorption coefficient by the sound absorption coefficient measuring device 76 of FIG. 1 will be described. First, the switches SW1,
A sound source signal 27 for measurement is output from the sound source waveform generating circuit 26 with SW2 and SW3 connected to the contact 1 side. In the stationary band noise method, uncorrelated band noise in each system (three systems) is used as the measurement signal 27. After the output of the band noise is started, when the sound field reaches a steady state, the switches SW1, SW2, and SW3 are turned to the contact 2 side to turn off the sound source. The impulse square integration method (Schr
In the case of the oeder method, a short tone (filtered impulse) is output from the sound source waveform generation circuit 26 as the measurement signal 27, and the switches SW1, SW2, and SW3 are immediately turned to the contact 2 side.

Switches SW1, SW2 and SW3 are connected to contact 2
By turning it to the side, an electroacoustic feedback loop 100 is formed, and the reverberation chamber 10 enters a reverberation attenuation process. In this reverberation decay process, the switching operation by the signal path switching circuit 80 causes
Spatial averaging of acoustic feedback is achieved. In addition, time-varying FIR
The parameters of the filters 82, 84, and 86 change every moment, and the boundary conditions of the measurement system slightly change, so that the loop gains of the signal paths 94, 96, and 98 of each system (three systems) are averaged in the frequency domain. (Flattened). By this averaging effect, the sound field diffusion is improved, and at the same time, the loop gain of the electroacoustic feedback loop 100 can be stably increased. As a result, the observed reverberation time is 1
It will be extended from double to several times. Then, as a result of the diffusion improvement of the sound field, the reverberation decay waveform approaches a smooth linear attenuation on the dB axis, and errors due to fluctuation and curvature of the reverberation decay waveform due to insufficient diffusion are almost eliminated.

In the reverberation decay process, the root mean squarer 4
0 corresponds to the input Pi (t) from each system.

[0029]

(Equation 1) Here, n outputs a score for averaging. Then, in the case of the stationary band noise method, the output of the root mean squarer 40 is supplied to the level recorder 43 to record a reverberation waveform. In the case of the impulse square integration method, the square averaging device 4
The output of 0 is supplied to the square integration analyzer 42 to obtain the spatial set average of the reverberation waveform. The above procedure is performed for the case where the sample 12 is arranged in the reverberation room 10 and for the case where the sample 12 is not arranged. By calculating the difference between the reverberation times in both measurements, the sound absorption coefficient of the sample 12 can be obtained.

FIG. 7 shows a reverberation decay waveform measured by the sound absorption coefficient measuring device 76 of FIG. This is a case where the signal at the contact 2 of the switches SW1, SW2, and SW3 is input to the root mean square device 40. The size of the reverberation room 10 used is 273 m ³ . (A ₀ ) shows the switching operation of the signal switching circuit 80 and the time-variant FIR filter 8.
2, 84 and 86 are turned off and the switch SW
With SW1, SW2 and SW3 tilted to the contact 1 side (Loop 1
00 is open), (a) is a signal switching circuit 8
0 switching operation and time-varying FIR filters 82, 84,
86, and switches SW1, SW2,
Keep SW3 down to contact 1 (loop 100 is open)
(B), the switching operation of the signal switching circuit 80 and the time-varying operations of the time-varying FIR filters 82, 84, 86 are turned on, and the switches SW1, SW2, and SW3 are turned off from the contact 1 together with the disconnection of the sound source waveform. This is a waveform when switching to the contact 2 (the loop 100 is closed). According to this, the switching operation of the signal switching circuit 80 and the time-varying FIR filter 8
By turning on the time-varying operations of 2, 84, and 86 and attenuating the reverberation while the loop 100 is formed, the reverberation attenuation waveform approaches a smooth linear attenuation as shown in FIG. It can be seen that errors due to fluctuations and curvatures are almost completely eliminated.

By using adders 102, 104 and 106 instead of the switches SW1, SW2 and SW3, as shown in a sound absorption coefficient measuring device 76 'in FIG. 8, the switching can be made unnecessary.

(Embodiment 2) FIG. 9 shows an embodiment of the power level measurement of a speaker according to the present invention. To measure the power level, in addition to the measurement of the sound pressure level in the measurement room, it is necessary to separately correct the measured sound pressure level with sound absorption power. Determined based on time measurements. Hereinafter, only the measurement of the sound pressure level will be described. In addition, the same reference numerals are used for the portions common to FIG. In this embodiment, the microphone constituting the electroacoustic feedback loop is also used as the measurement microphone. In the power level measuring device 108, a speaker 44 to be measured is arranged in the reverberation room 10. In addition, a plurality of microphones 46, 48, and 50 are arranged at appropriate locations in the reverberation room 10. A sound source signal 53 for measurement such as a pink noise or a wobble tone is output from a sound source waveform generating circuit 52, and is output from a speaker 44 via a power amplifier 54. Microphones 46, 48,
50 collects the sound radiated into the reverberation room 10. The picked-up signal is passed through head amplifiers 56, 58, 60 and a band-pass filter 62 for each system, and is used as a root mean squarer 64.
The output (sound pressure level) of each band is displayed on the level meter 66.

The outputs of the head amplifiers 56, 58 and 60 are A
It is input to the FC function unit 110. The configuration and functions of the AFC function unit 110 are the same as those of the AFC function unit 78 in FIG. The outputs of the three systems of the AFC function unit 110 are signal path 1
12, 114, 116 to power amplifiers 118, 12
The signals are supplied to the speakers 124, 126, and 128 disposed in the reverberation room 10 via 0 and 122, thereby forming three independent electroacoustic feedback loops 130 (that is, a plurality of independent signal paths).

A method of measuring the power level of the speaker 44 by the power level measuring device 108 shown in FIG. 8 will be described. The measurement sound source signal 53 is output from the sound source waveform generation circuit 52, and is output from the speaker 44. After the sound field reaches a steady state, the picked-up signals of the microphones 46, 48, 50 are supplied to a root-mean-squaring device 64 via a band-pass filter 62,
The result is displayed on the level meter 66. Thereby, the output (sound pressure level) for each band is obtained. The power level is determined by correcting the sound absorption of this output.

Although the number of systems of the electroacoustic feedback loop is three in each of the above embodiments, the number of systems may be two or four or more.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a sound absorption coefficient measuring apparatus according to the present invention, which is a plan view showing an arrangement in a reverberation room and a block diagram showing a system configuration.

FIG. 2 is a diagram showing a conventional sound absorption coefficient measuring apparatus, and is a plan view showing an arrangement in a reverberation chamber and a block diagram showing a system configuration.

FIG. 3 is a diagram showing a conventional power level measuring device for a speaker, and is a plan view showing an arrangement in a reverberation room and a block diagram showing a system configuration.

FIG. 4 is a side view of a reverberation room showing an arrangement state of a diffusion plate used conventionally.

FIG. 5 is a diagram showing an input / output switching operation of the signal path switching circuit 80 of FIG. 1;

FIG. 6 is a time-varying FIR filter 82, 84, 8 of FIG.
FIG. 9 is a diagram showing a time-varying operation of a parameter No. 6;

FIG. 7 is a reverberation decay waveform diagram showing a measurement example of diffusion improvement by the sound absorption coefficient measuring device of FIG. 1;

FIG. 8 shows switches SW1, S of the sound absorption coefficient measuring apparatus of FIG.
FIG. 14 is a diagram illustrating a configuration in which W2 and SW3 are replaced with adders.

FIG. 9 is a diagram showing an embodiment of a speaker power level measuring apparatus according to the present invention, which is a plan view showing an arrangement in a reverberation room and a block diagram showing a system configuration.

[Explanation of symbols]

Reference Signs List 10 reverberation room (measurement room) 12 sample to be measured for sound absorption coefficient 14, 16, 18, 124, 126, 128 speaker 20, 22, 24, 46, 48, 50 microphone 26 sound source waveform generating circuit (source for injection of sound source signal for measurement) 27, 53 Sound source signal for measurement 42 Square integration analyzer (measuring means) 43 Level recorder (measuring means) 44 Speaker for power level measurement (sound source) 52 Sound source waveform generating circuit (measuring sound source signal supplying means) 66 Level meter (Measuring means) 76, 76 'Sound absorption coefficient measuring device (acoustic characteristic measuring device) 80 Signal path switching circuit (signal path switching means) 82, 84, 86 Time-varying FIR filter (electrical transfer characteristic changing means) 94, 96, 98, 112, 114, 116 Signal path 100, 130 Electroacoustic feedback loop 108 Power level measurement device (acoustic characteristic measurement Device)

Claims (6)

[Claims] A plurality of microphones arranged in a measurement room; a plurality of speakers arranged in the measurement room; and a plurality of signal paths for supplying picked-up signals from the plurality of microphones to the plurality of speakers. And an electroacoustic feedback loop forming an acoustic feedback path in which sounds uttered by the plurality of speakers are acoustically returned to the plurality of microphones; and a plurality of independent signal paths from the plurality of microphones to the plurality of speakers. Signal path switching means for temporally switching the connection relationship between the plurality of microphones and the plurality of speakers to spatially average acoustic feedback; and electrical transmission characteristics arranged in the plurality of signal paths. Electrical transfer characteristic changing means for temporally changing the acoustic feedback signal to average in the frequency domain, and measuring means for analyzing the sound pickup signal from the microphone and measuring the sound. A, while improving the sound field diffusion characteristics of the measuring chamber, the acoustics measuring apparatus characterized by measuring the acoustic characteristics. 2. A plurality of microphones arranged in a measurement room in which a sample whose sound absorption characteristics are to be measured is arranged; a plurality of speakers arranged in the measurement room; and a plurality of speakers collecting sound signals from the plurality of microphones. An electro-acoustic feedback loop having a plurality of signal paths for supplying a sound uttered by the plurality of speakers and constituting an acoustic feedback path acoustically fed back to the plurality of microphones; and A signal path for spatially averaging acoustic feedback by temporally switching the connection relationship between the plurality of microphones and the plurality of speakers in a plurality of independent signal paths to the speaker at a rate of 3 to 30 times per second. Switching means; and electric transmission characteristic changing means arranged in the signal paths of the plurality of systems to change respective electric transmission characteristics with time so as to average an acoustic feedback signal in a frequency domain. And a speaker for measuring the sound source for measurement in the measurement chamber, which is provided also or exclusively for the speaker constituting the electro-acoustic feedback loop, and also serves as a microphone for constituting the electro-acoustic feedback loop or A measuring microphone provided exclusively for collecting sound in the measuring chamber, and measuring means for measuring an attenuation process of a collected signal from the measuring microphone after utterance of the measuring sound source is completed. An acoustic characteristic measuring apparatus for measuring an acoustic characteristic while improving a sound field diffusion characteristic in the measurement room. 3. A plurality of microphones arranged in a measurement room in which a sample whose sound absorption characteristic is to be measured is arranged; a plurality of speakers arranged in the measurement room; and a plurality of speakers collecting sound signals from the plurality of microphones. An electro-acoustic feedback loop having a plurality of signal paths for supplying a sound uttered by the plurality of speakers and constituting an acoustic feedback path acoustically fed back to the plurality of microphones; and Signal path switching means for temporally switching a connection relationship between the plurality of microphones and the plurality of speakers in a plurality of independent signal paths to the speaker to spatially average acoustic feedback; and Means for changing the respective electric transfer characteristics with time to average the acoustic feedback signal in the frequency domain, and said electro-acoustic feedback loop A measuring speaker, which is also provided as a dedicated speaker or is provided exclusively, and utters a measuring sound source in the measuring chamber; and measures an attenuation process of a sound pickup signal from the microphone after the utterance of the measuring sound source is completed. And measuring means for measuring acoustic characteristics while improving a sound field diffusion characteristic in the measurement room. 4. A plurality of microphones arranged in a measurement room in which a sample whose sound absorption characteristics are to be measured is arranged; a plurality of speakers arranged in the measurement room; and a plurality of speakers collecting sound signals from the plurality of microphones. An electro-acoustic feedback loop having a plurality of signal paths for supplying a sound uttered by the plurality of speakers and constituting an acoustic feedback path acoustically fed back to the plurality of microphones; and Signal path switching means for temporally switching a connection relationship between the plurality of microphones and the plurality of speakers in a plurality of independent signal paths to the speaker to spatially average acoustic feedback; and An electric transfer characteristic changing means arranged to change the respective electric transfer characteristics with time to average the acoustic feedback signal in the frequency domain; and any one of the signal paths. A sound source signal injecting means for injecting a sound source signal for measurement into a location and uttering the sound from the speaker; and a microphone which constitutes the electroacoustic feedback loop or is provided exclusively and collects the sound in the measuring chamber. A measuring microphone to measure, and measuring means for measuring an attenuation process of a picked-up signal from the measuring microphone after the utterance of the measuring sound source is completed, while improving a sound field diffusion characteristic in the measuring room. And an acoustic characteristic measuring apparatus for measuring acoustic characteristics. 5. A plurality of microphones arranged in a measurement room in which a sound source to be measured for sound pressure characteristics is arranged; a plurality of speakers arranged in the measurement room; and a plurality of sound pickup signals from the plurality of microphones. An electroacoustic feedback loop having a plurality of signal paths for supplying to the speakers, and forming an acoustic feedback path in which sounds uttered by the plurality of speakers are acoustically returned to the plurality of microphones; and Signal path switching means for temporally switching a connection relationship between the plurality of microphones and the plurality of speakers in a plurality of independent signal paths to a plurality of speakers to spatially average sound feedback; and An electric transfer characteristic changing means arranged in a path to change respective electric transfer characteristics with time to average an acoustic feedback signal in a frequency domain; and Measuring means for analyzing the collected signal from the microphone when the sound is being uttered and measuring the output level for each frequency band, while improving the sound field diffusion characteristics in the measurement room, An acoustic characteristic measuring device for measuring characteristics. 6. A plurality of microphones arranged in a measurement room in which speakers for which sound pressure characteristics are to be measured are arranged; a plurality of speakers arranged in the measurement room separately from the speakers to be measured; An electroacoustic feedback loop having a plurality of signal paths for supplying a sound signal to the plurality of speakers and forming an acoustic feedback path in which sound uttered by the plurality of speakers is acoustically returned to the plurality of microphones; A measurement sound source signal supply unit that supplies a measurement sound source signal to the speaker to be measured and utters the sound, a plurality of microphones and a plurality of speakers in a plurality of independent signal paths from the plurality of microphones to the plurality of speakers. Signal path switching means for temporally switching the connection relationship between the signal paths to spatially equalize acoustic feedback; and electric transmissions respectively arranged in the plurality of signal paths. Electrical transfer characteristic changing means for averaging the acoustic feedback signal in the frequency domain by changing the characteristic over time, and acquiring from the microphone when the measurement sound source signal is supplied to the speaker to be measured. A measuring means for analyzing a sound signal to measure an output level for each frequency band, and measuring an acoustic characteristic while improving a sound field diffusion characteristic in the measuring room.