Estimation of the lower cut-off frequency of an anechoic chamber: An empirical approach

Abstract

This paper deals with the development of an empirical expression to determine the lower cut-off frequency of an anechoic chamber when the source volume, chamber volume, wedge height as well as the major dimensions (i.e., total distance between the source and the chamber wall) are known. The frequency obtained from the empirical expression compares well within ±3% of the lower cut-off frequency obtained from the experiments. The paper also addresses the construction details and calibration procedure of the anechoic chamber. The chamber is calibrated by verifying the inverse square law for different directions from the sound source, and the lower cut-off frequency of the chamber is found to be 315 Hz within ±0.5 dB. Further, the fan broadband noise measurements are made, inside and outside, of the anechoic chamber in order to demonstrate the echo-free nature of the chamber and the spectra clearly shows that the chamber is anechoic for a broad range of frequencies.