Troy Gwin (left) and Travis Banks of ACS are shown with the EAW rig. Columbia, SC (July 26, 2007)--It's often noted that audio is not "rocket science." True enough--unless, of course, it is. Troy Gwin and his team at ACS Sound and Lighting, based in Columbia, SC, recently took on an "audio as rocket science" challenge presented by the University of Sound Carolina on behalf of Lockheed Martin Corporation and NASA (U.S. National Aeronautics and Space Administration), utilizing sound reinforcement technology to test a Space Shuttle rocket component.
ACS was tasked with duplicating the acoustic noise conditions found inside of rocket fuel tanks during liftoff, specifically, testing the effects of high sound-pressure levels on tiny (less than 1/4-inch diameter) acoustic sensors designed by Lockheed Martin to monitor SPL within the tanks. The test required generating electro-acoustic output (in this case, pink noise) matching a NASA response curve depicting constant SPL above 120 dB at 30 Hz to 10 kHz, with a peak in excess of 135 dB at 400 Hz. This output, conforming to the response curve, needed to be sustained for a period of three minutes at a distance of two feet.
To generate the output, ACS assembled a sound reinforcement system comprised of four cart-stacked EAW KF760 large-format line-array modules joined by two EAW BH760 horn-loaded subwoofers (a.k.a. "SuperSubs"), driven by Crown I-Tech power amplifiers and headed by a Yamaha M7CL digital mixer. The loudspeakers were aimed outdoors through a large back door at the ACS warehouse to avoid slap-back and reverberation generated by wall surfaces.
Then, to match the required output criteria, an Earthworks M30 measurement microphone (calibrated for SPL with a Metrosonics calibrator) was placed two feet in front of the loudspeakers, feeding EAW Smaart v.6 measurement software on a PC for analysis in matching the desired response curve.
"We did a number of short 'test runs' to optimally duplicate the curve, and then brought the system up to the required level," Gwin explains. "Smaart is a great tool for this--highly accurate while being so fast and intuitive to use."
Once the curve was matched, a piece of the carbon fiber fuel tank outfitted with the sensors was placed next to the measurement mic, and the official testing process commenced. Both setup and testing were conducted "after hours" to avoid disturbing neighboring businesses.
"It's important to remember this curve represents an 'envelop' that covers the levels of multiple rockets generated inside the fuel tank, and not on the launch pad," Gwin notes. "I can't imagine reproducing levels of an actual launch, and it's doubtful that it's even possible with a conventional sound reinforcement system." (Estimates of SPL for an actual NASA rocket launch place it well above 200 dB.)
"We were just informed that the sensors indeed passed the test, able to survive the tremendous output," he concludes. "All in all, it was an interesting project. And hey, it's the first time I've been wrong in saying, 'This is not rocket science' about our work."
ACS Sound and Lighting