Rigid foraminous microphone probe for acoustic measurement in turbulent flow

In combination, means defining a flow path for sound energy, a microphone probe comprising a tube disposed in said flow path and having a closed end facing the source of sound energy, a microphone disposed in said tube downstream in the direction of sound progation of said closed end, at least a portion of the length of said tube being composed of a rigid foraminouos plastic material containing a multiplicity of interconnected cells, said cells having an average size less than 100 microns.

A microphone probe for acoustical measurement in turbulent flow, comprising a tube to be disposed in a sound field and having a closed end facing a source of sound energy, a microphone disposed in said tube downstream in the direction of sound propagation of said closed end, at least a portion of the length of said tube being composed of a rigid foraminous sintered metal containing a plurality of interconnected cells, said cells having an average size less than 100 microns.

In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, an active attenuation system for attenuating undesirable output acoustic wave, comprising an output speaker introducing a cancelling acoustic wave;

• an error microphone probe for sensing the combined said output acoustic wave and said cancelling acoustic wave from said output speaker and providing an error signal, said microphone probe comprising a tube having a closed end facing said input acoustic wave, a microphone disposed in said tube downstreaam of said closed end, at least a portion of the length of said tube being composed of a rigid formaminous material containing a multiplicity of interconnected cells, and an adaptive filter model adaptively modelling said acoustic system and outputting a correction signal to said output speaker to introduce said cancelling acoustic wave.