Measurements in small rooms proposed for use as research laboratories indicated the presence of high amplitude infrasonic (i.e., at frequencies below 20 Hz) noise. Concern about this noise, which the author has further discovered to be common in many types of rooms, is due to the sensitivity to infrasound of the experiments proposed to be carried out in these spaces. This report describes measurement techniques used to discover the nature of this noise as the necessary first step in a mitigation program. Essentially, it was necessary to know whether the noise was due to air flow turbulence or was a pressure phenomenon coherent over the room volume such as would be found if the room behaved as a Helmholtz resonator. Measurements of the coherence of the pressure wave over large spatial areas within the room demonstrated the latter case. Data from measurements to demonstrate the coherence in turbulent flow are also shown for contrast.
M. Gendreau, “Measurement Techniques used to Verify the Cause and Nature of Low-frequency Noise in Rooms,” Proceedings of the 16th International Congress on Sound and Vibration (ICSV16), Kraców, Poland (5 to 9 July 2009)d2cd5f586962d650f38d1ba02f99f79b