Design and Construction of a Small Reverberation Chamber 2003-01-1679
As a manufacturer of a complete line of acoustical materials American Acoustical Products needed to construct a laboratory that would allow the characterization of the acoustical properties of its materials. Reference panels of materials were available that had been previously measured for absorption in a full scale reverberation chamber.
A design for a small reverberation chamber was developed based on the Toyota Specification TSL 0600G-4 which includes a small transmission window for STL measurements. This design has the advantage of being constructed with no parallel surfaces, is tall enough to walk into and is optimized for measuring samples between 9 and 30 square feet in surface area.
In order to allow the facility to function effectively several innovative techniques have been employed. To maximize the reverberation time the walls were constructed using constrained layer damped and mass loaded sheetrock on a timber frame. The walls and roof were constructed without cavities to avoid resonances and all the internal surfaces including the door and transmission window sealing panel were tiled with ceramic tiles for maximum reflectivity. The room's external surfaces were lined with sound absorbing foam to improve the sound transmission loss measurements.
To generate a diffuse sound field, the chamber was excited by a NXT® Distributed Mode Loudspeaker which has virtually no directivity. To measure the room response, pressure zone microphones were placed in the corners of the room where all the resonant modes have pressure maxima. Finally the analysis of the RT60 sound decay was measured by a two channel real time analyzer using a studio mixing desk to switch between microphones.
Results from the small reverberation room will show how closely the measurements agree with the full scale tests carried out to ASTM C423 at the Hudson Valley Acoustics Laboratory12