Design of a New Testing Chamber to Determine the Absorption, Diffusion and Scattering Coefficients

This presentation will describe a design for a new 286 m3 testing chamber that will allow the measurement of the random incidence absorption coefficient, according to ISO 354, the scattering coefficient, according to ISO 17497-1, the diffusion coefficient, according to ISO 17497-2 and the normal incidence low frequency absorption coefficient, according to ISO 10534-2. Optional dimensional ratios were determined by minimizing the standard deviation of the modal response. Both dome-shaped boundary diffusors and hanging panels are used to provide satisfactory diffusivity, which is verified using a 200 mm reference absorber according to ISO 354. The isotropy of the incident sound is measured with a new Sound Field Analysis Recorder (SOFAR) and quantified by an analysis of the wavenumber spectrum. A sufficiently large reflection free volume is provided in the chamber for boundary method diffusion coefficient scale model goniometer measurements. A new FDTD simulation program will be described to determine the diffusion and scattering coefficients of any 3D surface in the near and far field. A steel and concrete lined low frequency impedance tube measuring 600 mm x 600 mm x 5.8 m long and 7 tons will be used to measure absorption from 25-250 Hz.