Tuning of Estimated Sound Absorption Coefficient of Materials of Reverberation Room Method

Abstract

Acoustical materials are usually used for architectural design, ambient noise, and traffic noise to absorb sound. The sound absorption coefficient (SAC) is often used as the performance index of acoustical materials. It is measured using the reverberation room method (RRM) and the impedance tube method (ITM). The sound source of the RRM is a random incidence in various directions, whereas that of the ITM is a normal incident. The SAC measured by the RRM is more extensive, practical, and costly than ITM. Usually, the SAC measured by RRM is used as the commercially available acoustical materials index. However, RRM requires large-area test samples for measurement and a special sound field of reverberation room for test experiments. Therefore, this study aims to use the ITM to measure SAC. The measured SAC, frequency, thickness, and material density were employed as independent variables and substituted in the obtained multiple regression model to predict SAC obtained by RRM. In addition, the measurement characteristics of impedance tubes provide varisized calibers for different frequency ranges to measure a relatively accurate SAC. Based on the abovementioned characteristics, this study proposed a dual-model for estimating the SAC of the reverberation room method to achieve the best-estimated result. After experimental validation, the dual-model estimated result was compared with SAC from the reverberation room method. It was observed that the maximum absolute value of all errors did not exceed 0.16. Most of the absolute errors were below 0.1, proving the accuracy of this method. Therefore, the method proposed in this study can shorten the acoustical material development schedule for manufacturers and save the cost of the development process.

Sound Absorption Measurement: Alpha Cabin and Impedance Tube

“…This test method is similar to the previous method in that it uses the same experimental scheme with a sound source at one end and a sample fixed in an impedance tube at the other end. The procedure is described in detail in [10,11]. In this test method, plane waves in the tube are excited by a noise source and the sound pressure is measured by microphones located at two fixed points (or by one microphone moved in the tube) and by subsequent calculation of the complex transfer function at a perpendicular incidence of sound waves.…”

Fabrication, characterization, and application of the water hyacinth biochar-polyvinyl alcohol composite as an advantageous sound absorber material

“…The impedance tube shown in Fig. 1 was assembled according to references [30][31][32][33] with a little bit of modification. As can be seen in Fig.…”