Tubular windscreen design for microphones for in-duct fan sound power measurements

Abstract

The design of tubular windscreens (sometimes called sampling tubes) for in-duct fan sound power measurements is described. Such sampling tubes might be used in the field, although the motive for the present study was the development of a windscreen (sampling tube) for use in an in-duct fan sound power measurement standard. The head-on frequency response, directivity, and turbulence rejection of several different designs of sampling tubes have been measured. A theory to predict head-on frequency response and directivity of the sampling tube has been developed. The basic governing equations were derived from the conservation of mass and conservation of momentum with the assumption that the particular thermodynamic process is an adiabatic one. The theoretical results are in good agreement with the experimental results.