ACOUSTIC NOISE REDUCTION IN SHIELDED ENCLOSURES.
Final technical rept. for Jun-Aug 65,
NAVAL CIVIL ENGINEERING LAB PORT HUENEME CALIF
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The acoustic NR noise reduction for a shielded enclosure at NCEL has been determined. The instrumentation necessary for measuring NR in the frequency range between 100 and 15,000 Hz has been established. All measurements make use of an air-borne signal source which is capable of providing approximately 60 db dynamic range in signal-level measurement. A standard method and a swept-frequency method were used to measure NR. The two methods are compared in this report. The far-field and near-field NR values have been measured for a 20x20x10-foot shielded enclosure. The vibration level measured with an accelerometer at the walls of the enclosure have also been determined. The minimum noise-reduction near-field values were on the order of 10 db at 1,500 Hz. Far-field NR measurements yield values from 12 to 45 db from 100 to 10,000 Hz. Author