Non-linear generation of acoustic noise in the IAR spacecraft

The requirement to produce high level acoustic noise fields with increasing accuracy in environmental test facilities dictates that a more precise understanding is required of the factors controlling nonlinear noise generation. Details are given of various nonlinear effects found in acoustic performance data taken from the IAR Spacecraft Acoustic Chamber. This type of data has enabled the IAR to test large spacecraft to relatively tight acoustic tolerances over a wide frequency range using manually set controls. An analog random noise automatic control system was available and modified to provide automatic selection of the chamber's spectral sound pressure levels. The automatic control system when used to complete a typical qualification test appeared to equal the accuracy of the manual system and had the added advantage that parallel spectra could be easily achieved during preset tests