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 Laboratory
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ISO R354:1985 “Measurement of sound absorption in a reverberation room”
ASTM C423-99a “Sound absorption and sound absorption coefficients by the reverberation room method”
ASTM C384-98 “Impedance and absorption of acoustical materials by the impedance tube method”
The Rieter Automotive ALPHA CABIN System: http://www.rieter.com/auto/tech/PDFs/ALPHA_CAB.pdf
Renault Test Method 32-00-D13 “Acoustic absorbent - Absorption in a diffuse field 6/91 English Translation)
Toyota Test Method TSL 0600G-4
“The distributed mode loudspeaker, principles and practice” Bank Graham Dr - New Transducers Ltd - Noise & Vibration Identification & Treatment Symposium & Exhibition - Engineering Integrity Society November 2000
NXT plc, Hinchingbrooke Business Park, Huntingdon, Cambs PE29 6FW http://www.nxtsound.com/
CROWN Audio, Inc. P.O. Box 1000, Elkhart, IN 46515-1000 http://www.crownaudio.com/mic_htm/pzm.htm
Larson Davis 1681 West 820 North, Provo, Utah 84601 http://www.lardav.com/2900b.html
Larson Davis 1681 West 820 North, Provo, Utah 84601 http://www.lardav.com/DNA.html
IBM Hudson Valley Acoustics Laboratory NVLAP Lab Code: 100323-0
Cornerstone technical data analysis software, Brooks-PRI Automation, http://www.brooks.com/products-redirect/POBU/cstone/multireg.htm
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