High intensity noise generation for extremely large reverberant room test applications

Abstract

A recent operational need for the development of a large (101,000 ft 3) reverberant acoustic chamber at the Space Power Facility of NASA Glenn Research Center's Plum Brook Station with the requirement of generating sound pressure levels (SPL) as high as 163 dB has resulted in the need to re-examine the generation of noise in reverberant rooms. Early in the design stage, it was realized that the acoustic power level capability (10-30 kW) of conventional electrodynamic air modulators, such as those supplied by the Wyle Corporation, would be required in unprecedented numbers to meet the test spectra requirements. The design team then turned to a lesser known modulator, the hydraulically driven air modulator supplied by the Team Corporation, which has 150-200 kW acoustic power capability. The advantage to the project was a significant reduction in the number of modulators required to meet the requirements. However, since only limited characterization of Team modulator's performance has been reported, a test program was required in order to mitigate the risk of the design of the RATF. Aiolos Corporation, which is responsible for the acoustic design of the RATF, and the Institute of Aerospace Research (IAR) of the National Research Council of Canada (NRC), entered into a collaborative agreement with the objective of characterizing, optimizing and investigating the controllability of the Team modulators. The test program was performed at the NRC-IAR reverberant chamber, a 19,000 ft3 facility located in Ottawa, Ontario, Canada. The current paper provides details of the principle of operation of the Team modulators, including their servo control loops and provides of a summary of the characterization and controllability test program.