Accession Number : AD0455966


Title :   REDUCTION OF MICROPHONE WIND NOISE BY THE GENERATION OF A PROPER TURBULENT FLOW,


Corporate Author : TEXAS WESTERN COLL EL PASO SCHELLENGER RESEARCH LABS


Personal Author(s) : Ballard, Harold N ; Izquierdo, Mike


Report Date : Feb 1965


Pagination or Media Count : 19


Abstract : A detailed theoretical and experimental study was made of the acoustic and noise reducing characteristics of a line microphone which is an outgrowth of the noise-reducing line microphone of Daniels. Modifications were made to the basic line microphone design and the acoustic characteristics of the modified system were determined. The information gained from this study, coupled with the theoretical implications of the NavierStokes equation for fluid flows at large and small Reynolds numbers and a consideration of the velocity-gradient-dependent nature of the viscous forces acting within a fluid, led to utilization of a new concept to reduce the flow speed of the air stream over the microphone system. This is accomplished by the use of a screening device which creates a turbulent flow of the proper characteristics so as to dissipate the flow energy of the air stream without interfering with the reception of the desired acoustic signals. Wind tunnel and field test records are presented which indicate that the underlying basic concept is correct and that the wind-noise generated by the interaction of the wind stream with an open low-frequency response microphone (0.1 to 50 cycles/sec) can be reduced by a factor of 30 db at a wind speed of 20 miles/hr. (Author)


Descriptors :   *NOISE , WIND , MICROPHONES , REDUCTION , ACOUSTIC PROPERTIES , EQUATIONS , TURBULENCE , VELOCITY , REYNOLDS NUMBER , FLUID FLOW


Distribution Statement : APPROVED FOR PUBLIC RELEASE