A special-purpose convertible anechoic/hemi-anechoic
facility was designed for NASA to facilitate measurement of the noise emission
of spaceflight hardware components. The Fluids Integrated Rack (FIR) is
shown below under test. Several special considerations had to be
included in the design: special (and potentially noisy) support equipment,
large test articles, intrusive environmental noise from aircraft flyovers, and
special requirements related to handling of spaceflight equipment.
A computer manufacturer required a quiet multi-chamber
facility to be located within a standard-construction commercial building that
also housed shock- and vibration testing equipment, forklift traffic and other
technical activities. Ambient sound levels within the chambers were to
approximate auditory threshold. The project
included guiding the design of the laboratory space (walls, floors, ceilings,
HVAC, etc.) as well as designing one of the test chambers.
A client uses a reverberation chamber for sound power testing of appliances. One challenge in performing this test is a low-frequency
tone that is often present, causing the standard deviation of the sound
pressure level readings at the various mics to be excessive.
By developing a mathematical model of the distribution of sound in the
reverberation chamber, it was possible to identify the microphone locations that gave readings closer to the
presumed "true" mean and gave a smaller standard deviation as
well.
The graphic
at right shows the level of a low-frequency tone at a particular
altitude in the chamber, superimposed over boundaries as defined by the test
standard, source locations, and
proposed microphone locations. Double-click to see a full-size image.
