Reverberation time measurement of a structure or a room using modified wavelet transform

Abstract

In structure damping or acoustic decay measurement using the third-octave band pass filter, there is inevitable experiment error produced by ringing at the tail part of the impulse response of the filter. This ringing gives rise to the distortion of the decay curve. To reduce this error, it has been recommended that the product of the 3 dB bandwidth B of the filter and the reverberation time T of the system is at least 16. In case of a system having a short reverberation time the decay curve cannot be measured reliably using the filter. In this paper, the modified wavelet transform (MWT) has been proposed to determine accurately the decay curve with a low value of BT. The MWT decomposes the decay signal of a system into time–frequency domain using the third-octave band wavelet filter bank. When the MWT is applied to the measurement of the decay curve, it is found that the requirement BT<16 can be replaced by the replacement BT<4. It was applied to the reverberation time measurement of a small room and the identification of impact location occurred by a loose part in the nuclear power plant. [Work supported by Nuclear Research Project in Korea.]