low frequency noise in sound booth ("Ferguson, Sarah Hargus" )

Subject: low frequency noise in sound booth
From:    "Ferguson, Sarah Hargus"  <safergus@xxxxxxxx>
Date:    Fri, 14 Dec 2007 15:35:49 -0600

Hello list - I've run into a very annoying problem in my (double-wall) sound booth. When I try to calibrate, I'm getting floor noise of 75-80 dB SPL WITH the earphone (which isn't connected to anything) on the 6 cc coupler, WITH the door closed. The spectrum analyzer shows a peak around 65-70 dB SPL at 16 Hz, with energy about 20 dB below that at 12 and 20 Hz - and nothing else, really. I have two questions: 1) Does any one have any ideas about what could be causing this? Three gentlemen from Facilities Operations worked on this for over an hour this morning, turning off lights and air handlers and exhaust fans - they even went out on the roof to turn things off. Nothing that they did had any impact on the noise. 2) How low can I reasonably expect my floor noise to be? While trying to pin down the onset of this noise, I realized that I never write down the level of the floor noise, just the levels of the sounds I'm calibrating (which have often been at levels much lower than 75 dB SPL). With all this troubleshooting I've completely lost my bearings about what I SHOULD be getting. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Sarah Hargus Ferguson, Ph.D., CCC-A Assistant Professor Department of Speech-Language-Hearing: Sciences and Disorders University of Kansas Dole Center 1000 Sunnyside Ave., Room 3001 Lawrence, KS 66045 office: (785)864-1116 Speech Acoustics and Perception Lab: (785)864-0610 http://www.ku.edu/~splh/Faculty/FergusonBio.html

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Electrical Engineering Dept., Columbia University