The acoustic chamber is highly absorptive
up to 50 kHz , and has been used for ultrasonic experiments
at those frequencies.
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
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
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
Four GRAS surface microphones
One PCB Piezotronics high-sound
Four Shure microphones for speech
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
40 dB at 63 Hz
70 dB above 250 Hz
80 dB above 1 kHz
Anechoic chamber noise floor
(weighted and unweighted data).
Click image for larger
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.
image for larger view.
Southwest Research Institute® (SwRI®), headquartered
in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied
engineering and physical sciences research and development organization with