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 SOUTHWEST RESEARCH INSTITUTE

 

Acoustic Test Facility

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  Image: The acoustic chamber is highly absorptive up to 50 kHz , and has been used for ultrasonic experiments at those frequencies.
 

The acoustic chamber is highly absorptive up to 50 kHz , and has been used for ultrasonic experiments at those frequencies.

  Image: 0.04- to 110-GHz Millimeter Wave S-Parameter Vector Network Analyzer
 

View through the reverberation chamber into the anechoic chamber through the 6-ft. by 6-ft. opening. The Altec Lansing A7 speakers are shown in the foreground. Also shown are the reflectors (ceiling) used to calibrate the reverberation chamber to obtain a nearly perfect hemisphere of sound directed into the anechoic chamber.

Acoustic testing is performed in a chamber designed to thin or minimize sound waves or electromagnetic energy. The size and type of chamber can vary, depending on the size of the test object and the type of measurements sought.

 

The acoustic test facility at Southwest Research Institute (SwRI) consists of an anechoic chamber, a reverberant chamber, and a control center. The two chambers can be used separately or they can be connected via a removable 6-foot by 6-foot partition. When connected, the chambers are useful for sound transmission loss (STL) testing, as well as response testing of flat surfaces.

 

Anechoic Chamber Features

  • 18-foot by 18-foot working area

  • Free-field equivalent out to a 13-foot radius, according to ISO 3745 Annex A, from 63 Hz to 20 kHz

  • Highly absorptive up to 50 kHz; has been used for ultrasonic experiments at those frequencies

  • Noise floor estimated to be < 6 dBA

Reverberant Chamber Features

  • 20-foot by 20-foot area

  • Used by itself for sound emission measurements

  • Can be arranged to conform to ISO/TR 7849:1987 standards for estimation of airborne noise emitted by machinery using ISO 3741-3743 procedures

Various types of test signals can be created and driven by our Audio Precision ATS-2 and SYS-2722A 2700 series audio test sets, allowing us to synthesize and record test signals up to 386 kS/sec. We routinely use MATLAB® for waveform creation and analysis on a control center computer.

 

The instrumentation set includes:

  • One Bruel and Kjaer 4722 microphone on a rotating boom

  • Four GRAS surface microphones

  • One PCB Piezotronics high-sound intensity microphone

  • Four Shure microphones for speech recordings

  • One pair of Altec Lansing A7 speakers, which have a frequency response of 10 dB, sensitivity of 1 watt at 1 meter and crossover frequency of 900 Hz. Speaker dimensions are 30 in. wide by 24 in. deep by 54 in. high, and nominal coverage is 90° horizontal and 40 vertical.

Sound attenuation across the partition is measured as:

  • 40 dB at 63 Hz

  • 70 dB above 250 Hz

  • 80 dB above 1 kHz

 

 

 

Image: Anechoic chamber noise floor (weighted and unweighted data).   Image: A representative sound field measured in the reverberant chamber. We can excite the reverberant chamber with noise, swept sine tones, or arbitrary waveforms for the purpose of creating high intensity sound fields or measuring sound transmission loss through materials at sound pressure levels up to 125 dB.

Anechoic chamber noise floor (weighted and unweighted data). Click image for larger view.

 

A representative sound field measured in the reverberant chamber. We can excite the reverberant chamber with noise, swept sine tones, or arbitrary waveforms for the purpose of creating high intensity sound fields or measuring sound transmission loss through materials at sound pressure levels up to 125 dB. Click image for larger view.

 

Other electromagnetic compatibility research facilities are available at SwRI. Visit Structural Dynamics and Product Assurance.

 

For more information about our acoustic test facility, or how you can contract with SwRI, please contact Jose Navarro at jnavarro@swri.org or (210) 522-5292.

 

acoustictest.swri.org

  

Contact Information

Jose Navarro

Acoustic Chamber

(210) 522-5292

jnavarro@swri.org

acoustictest.swri.org

Related Terminology

ultrasonic experiments

sound emission measurement

airborne noise emissions

test signal creation

acoustic test facility

reverberant chamber

 

Dept of Engineering Applications and Systems Development

| Department of Engineering Applications and Systems Development | Applied Physics Division | SwRI Home |

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.

August 07, 2014