Abstract
A new method to measure of partial sound absorption characteristics using simple circuits of phase shifter and multiplier is proposed. As shown in Fig. 2, these circuits are used to measure amplitudes and phase conditions of the input and reflected sound at the surface of a test material and a reference rigid board over layed on it. Amplitude of a input sound pressure is obtained from the outputs to be maximum and zero by tunning the phase shifter on the measurement of the rigid board. Real and imaginary parts of reflected sound from the test material also are obtained as outputs by tunning to the same positions. Filary, sound absorption coefficient can be caluculated. The new method, based on a correlation technique, have a feature of registant to intefering noise. So, this method is available for checking characteristics of absorbents under construction, and also available for searching wrong part in the case when unexpected acoustical conditions have been found out after construction. As the test of practical use, indoor and outdoor field measuments were carried out. As for two perforated plate walls, clear differences between typical and wrong characteristics could be obtained. See Fig. 18. As for a pervious pavement surface under the condition of interfering noise, it could be found that absorption characteristics were similar to those of pourous absorbent.
