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A High Intensity Infrasonic Acoustic Test System
ARMY RESEARCH LAB ADELPHI MD
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We describe the design, mathematical modeling, construction, and test of an acoustic test system intended to support the performance of high-intensity acoustic effects experiments on large targets at low-sonic to infrasonic frequencies. An early experimental version of the system, HILF1, used a compressed-air source and airflow modulator from the ARL Mobile Acoustic Source MOAS and a single-volume Helmholtz resonator test chamber to achieve sound pressure levels SPL above 140 dB in a 5-cu m volume. Based on results from this system, a more advanced system, HILF2, was designed and built. HILF2 uses a compressed-air source based on automotive superchargers, a low-impedance airflow modulator, and a two-volume Helmholtz resonator test chamber to achieve sustained high-purity sinusoidal sound pressure levels in excess of 155 dB in a 2.5-cu m test volume at frequencies from 2 to 20 Hz.
APPROVED FOR PUBLIC RELEASE