Development of a Portable Anechoic Chamber and Characterization using Reverberation Time

Abstract

Reverberation time measurement technique is in general used to understand building acoustics and response of acoustic liners. However, the background noise level is used to characterize an anechoic chamber. For that a free field microphone is required having high bandwidth and response to very low noise level, which is expensive. Quoting the statement “necessity is mother of invention”, present research aims to characterize a portable anechoic chamber by using reverberation time measurement using a microphone. The paper has two sections. First section describes the fabrication of a portable anechoic chamber and the second section describes the characterization of the chamber using reverberation time. In this section, a customized measurement technique has been proposed using a novel signal processing technique, based on pseudo sampling, which enhances the performance in measuring very low reverberation time such as T60≈0.02 seconds in total spectrum and in octave bands. The octave band analysis also helped to understand the frequency bandwidth of the chamber for measurement. Subsequently, acoustic insertion loss across a finite sonic crystal has been measured in this chamber. The measurement has been evaluated numerically in a nonreflecting acoustic domain by applying characteristic acoustic impedance on the acoustic domain wall. The numerically estimated results agree to experimentally measured data up to large extent. From this exercise, it has been inferred that the portable anechoic chamber wall is equivalent to a nonreflecting boundary. Summarizing, the proposed reverberation time measurement technique can be used to characterize any anechoic chamber