Reverberation characterization inside an anechoic test chamber at the weapon sonar test facility at Naval Undersea Warfare Center Keyport Division

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The Weapon Sonar Test Facility (WSTF) at NUWC Keyport, WA, is a 34 500 gallon pressure tank currently used for test and evaluation of torpedo sonar arrays. The tank has many more possible uses and complete characterization of the testing environment needs to be performed. One of the methods of characterization being used is the determination of the reverberation time of the anechoic chamber. Applying Sabine-Franklin-Jaeger theory of reverberant rooms, an experimentally determined reverberation time T60 for a “live room” can be used to provide an upper bound for the reverberation time in the chamber. Utilizing the Eyring theory of “dead” rooms will provide a better determination of T60 for the anechoic chamber, hence provide a lower bound characterization. The experimental method involves determining the spatially averaged acoustic energy of an initial tone and the corresponding reflection from the chamber wall seen in a recorded signal. These values determined from the root mean square signal voltage determine the wave decay time, τ. The decay time is directly related to the reverberation time through T60 = 6τ×loge10. The reverberation was determined to be within an acceptable tolerance for testing and evaluation.