Sound absorption coefficient by reverberation room method is a popular way of evaluation of the sound absorbing property of acoustic materials. It is obtained from the two measured reverberation times when a specimen is placed in a reverberation room, and when it is not placed. The reverberation time is calculated from the decay of the sound pressure level as a function of time at a certain point in the room.
Generally, it has been considered to be the averaged sound absorption efficiency of the acoustic material for various angles of sound indcidences, and been widely used as an index for evaluating sound absorbing efficiency of acoustic design of a concert hall, interior materials for automobile, construction materials and so on.
The measurement method used in this system follows the standard, ISO 354 and JIS A 1409. And to obtain the reverberation time, it supports not only the interrupted noise method specified by these standards but also the integrated impulse response method. Of course these two methods are expected to have the same results in theory; the latter brings higher accuracy and repeatability of measurement results of the reverberation time than the former.
The integrated impulse response method requires a one-shot measurement of the room impulse response to determine the reverberation time. This contributes to shorten the measurement time as well. However, the former method requires great number of averaging of the sound pressure decay curve, at each microphone position in order to achieve an acceptable repeatability.
Moreover, to improve the accuracy of the sound absorption coefficient in a reverberation room, especially in a small room, various R&D studies have been examined from the several points of view like room shape, diffusing panels, measurement method, and so on. These R&D studies and outcomes are reflected onto our measurement system. In addition, this system can be used for the scaled-model experiment of ultrasonic range.
In general, sound absorption coefficient can be obtained from the averaged reverberation time at several points in a reverberation room. Since this system is available to perform multichannel measurement, which realizes to obtain the averaged reverberation time in one-shot measurement and reduces the unwanted affect to the measured reverberation time due to the change of temperature and humidity with time. From this point of view, the eight channel measurement system has been used in our small reverberation room to obtain the measurement data with excellent reliability within very short time.
|Method||The integrated impulse response method, interrupted noise method (ISO 354, JIS A 1409)|
|Number of input/output channels for multichannel measurement||Number of output channel: 32 channels (max)
Number of input channel: 32 channels (max)
(depends on the spec of PC)
|Audio interface (sound card)||Ask for the recommendations|
Depends on the size of reverberation room and audio interface.
|PC||OS: Microsoft Windows 2000 / XP
Intel Pentium 4 or faster CPU and 1GB or more RAM are recommended.