An Investigation of the Low Frequency Sound Field of a Reverberant Enclosure and the Effects of Digital Electronic Feedback

摘要

The goals of this research has been to investigate the low frequency fluctuation of the characteristics of the sound field in comparison to those characteristics at high frequency and to implement electronic feedback, using a single Finite Impulse Response (FIR) filter, to beneficially change the degree of diffusion to increase the useful frequency range of reverberant enclosures for sound power measurements. This investigation included a computer model study and an experimental study in a model (6.82 cu. m) enclosure of the frequency-by-frequency fluctuation of the time-averaged spatial mean squared pressure as it relates to sound power measurements; the normalized spatial variance, the probability density function and the cumulative distribution function of time-averaged squared pressure normalized to the spatial mean; the spatially averaged cross correlation coefficient; and the vector intensity. In this study, the open loop response and the fluctuations of the enclosure transfer function with source and receiver positions, wall absorption, and temperature have been investigated. The data from both the computer model and the experimental model showed that the feedback implemented in this study did not significantly affect the diffusion of the sound field.