Determining and Comparison of Sound Absorption Coefficients using Small Reverberation Chamber and Test Tube Methods

Abstract

Sound absorbing materials have been widely used to decrease hazardous noise in indoor and outdoor environments. In the present study, we designed and constructed an experimental laboratory-scale chamber to measure the sound absorption coefficients of porous materials in comparison with the measurements of the test tube method. The main reason was to design and construct a small chamber to enable testing of acoustic material samples in small dimensions allowing easy and rapid testing of acoustic materials. The acoustic chamber method was based on the formation of reverberation field of the acoustic waves across testing chamber locations, but differences in sound pressure throughout the chamber may result in measurement errors. Therefore, the chamber was constructed with a volume of 2.85 m3, wall reflectors, and a rotating sound source was designed to ensure a diffusive field. The tests were conducted with samples of 12.4m2 installed on interior surfaces of the chamber. Sound absorption coefficients of acoustic polyethylene and polyurethane absorbents were measured across the central frequencies of the octave band. Sound absorption coefficients under reverberant random incidence and normal incidence were related to the sound frequency. The chamber method predicted higher sound absorption coefficients compared to the coefficients obtained by the tube test method for all tested porous materials. Based on the results of the proposed small chamber, it can be concluded that sound absorption coefficients measurement of samples in an environment was more similar to real situations.