Novel silencers and absorbers for wind tunnels and acoustic test cells

Abstract

Low frequency noise measurements in reverberation and free-field rooms require special attention as the sound field in this frequency range may be dominated by only a few modes (eigenfrequencies). This paper shows how reverberation rooms may be adequately damped to smooth the spatial sound field and to increase reproducibility and repeatability without violating the standards. Absorber modules and their operation principle are presented which are only 250 mm thick and are used as lining for test cells and wind tunnels providing free-field conditions down to 50 Hz for 1/3-octave band measurements. Their high acoustic effectiveness is proved by measurements in well-conditioned test rooms and with measurements in realized projects.