Abstract: The detection of sound emitted from a source in a dynamic environment of ambient background noise employs a sufficiently distributed array of sound intensity probes enclosing a sound source is adapted to collect measurements over the same time interval in a non-specific acoustic environment. Each probe in the array is comprised of a pair of mutually spaced microphones generally unmatched in their gain and phase response. A multi-channel fourier spectrum analyzer is used to provide a direct signal processing determination of sound intensity at each probe from pressure measurements taken at each microphone. Their computation is corrected to compensate for gain and phase mismatch between each microphone pair using independently derived probe calibration factors. These correction factors are linearly applied to the sound intensity determination at each probe of the array.

Abstract: A calibrator and the derivation of an associated calibration data base for computationally compensating for gain and phase mismatch in sound intensity probes comprised of two unmatched pressure transducing microphones is described herein. The calibrator utilizes a unique `phase plug` to maintain temporal uniformity (in addition to standard spatial uniformity) in the sound field of the calibration chamber. Gain and phase calibration factors are independently obtained for each probe of interest using the calibrator and these data are compiled into an independent data base for storage and subsequent application. Such linear correction factors as applied to associated signal processing of probe measurements serves to computationally compensate for phase mismatch between the unmatched microphone pair.

Abstract: An electrical motor with integral silencer is provided having a motor housing defining an inlet aperture at one end and an expansion chamber at the other end. The expansion chamber has a reduced cross-sectional area at the entrance and exit of the expansion chamber compared to the cross-sectional area of the chamber. The exit of the expansion chamber provides an outlet aperture in the housing. A stator is situated in the housing and a rotor is rotatably mounted within the stator. A fan is secured to the rotor and rotates therewith for pulling air in the outlet aperture through the stator and exhausting the air through the expansion chamber to the housing exterior. The expansion chamber provides an impedance mismatch for the acoustic energy generated by the fan preventing a portion of the acoustic energy from exiting the expansion chamber.