ANALYSIS OF ACOUSTIC FIELD DIFFUSIVITY FOR THE DETERMINATION OF THE SOUND ABSORPTION COEFFICIENT IN A REVERBERATION CHAMBER

Abstract

The Laboratory of Acoustics and Vibrations of INTI is fine-tuning a system for determining the sound absorption coefficient in a reverberation chamber using the interrupted noise method following the guidelines of IRAM 4065:2019. The study focuses on two main aspects: the analysis of sound field diffusivity through the addition of diffusers and the estimation of uncertainties of the method with particular emphasis on the uncertainties associated with the volume of the reverberation chamber and the reverberation times.

To generate a uniform sound field, rectangular acrylic diffusers and high-density polystyrene spheres are used. Reverberation time measurements between 500 Hz and 4000 Hz are compared for different diffuser configurations, with the configuration consisting of 10 acrylic panels and 3 polystyrene spheres showing the least dispersion in the measured times. Regarding the uncertainty estimation, the one associated with the calculation of the reverberation chamber volume is estimated using a variational method employing the ''Delaunay'' class from the ''scipy.spatial'' module of Python, resulting in approximately 10% of the measured volume of the chamber. Finally, a calibration method for the reverberation time measured with the dual-channel analyzer Building Acoustics Analyzer model 4417 is presented, where synthetic sound pressure level decay curves are generated over time from pure tones filtered in one-third octave bands and electronically injected into the analyzer to determine its uncertainty.