DESIGN AND MEASUREMENT OF INFRASONIC GRADIENT MICROPHONES AND WINDSCREENS

Until recently, infrasonic phenomena have been explored mainly with pressure microphones. Gradient microphones, especially when arranged in an orthogonal bigradient array, have the capability of providing information about the direction, as well as the intensity and time of sound arrival. A low frequency bigradient array is described. An equivalent circuit for analyzing infrasonic gradient microphones is developed and applied to the analysis of errors that may be expected when the microphone is measured in a spherical field. A plane wave calibrator for infrasonic gradient microphones and windscreens, with internal dimensions of 4Ã 4Ã 8 ft, has been built along the principles of the laboratory calibrator for gradient hydrophones described by the present author [J. Acoust. Soc. Amer. 39, 585 586 (1966)] with the added capability for testing the acoustical symmetry of infrasonic microphones. Windscreens affect the low frequency response of gradient microphones and the new equivalent circuit has been applied to the design of windscreens. © 1968, Acoustical Society of America. All rights reserved.