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Re: low frequency noise in sound booth

Dear List

We've had the exact same calibration problems in our sound booths - mostly caused by a ventilation system that produced very large SPL in the 10-20 Hz region. 

When using a portable sound level meter, there is often not a selectable high-pass cut-off. However there is often the option to select 'C' weighting which is much flatter than the 'A' weighting - flat from 100 Hz - 3 kHz and thus well suited for speech level calibration. So that has been our solution to the calibration issue.

There is a good overview of weighting functions on http://en.wikipedia.org/wiki/A-weighting



Lars Bramsløw, Ph.D.
Oticon A/S, Audiology
Kongebakken 9
DK-2765 Smørum

+45 39 13 85 42

-----Original Message-----
From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Stuart Rosen
Sent: 15. december 2007 08:56
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: low frequency noise in sound booth

I too have had this problem. In our quiet room in central London, you 
can in fact, just about hear the tube trains as they pass under our 
building. But even when it appears to be completely silent, our spectrum 
analyser shows strong low frequency sound.

But A-weighting is not necessarily the best way to deal with this 
problem and is often inappropriate depending upon what one is trying to 
measure. Our spectrum analyser has the option of summing the power over 
a specified frequency range, so I simply restrict the measuring range to 
something like 50 Hz-10 kHz.

Yours - Stuart

Stuart Rosen, PhD
Professor of Speech and Hearing Science
Dept of Phonetics & Linguistics
4 Stephenson Way
London NW1 2HE

Directions to Wolfson House (where I am based):

Tel:   (+ 44 [0]20) 7679 7404
Admin: (+ 44 [0]20) 7679 7401
Fax:   (+ 44 [0]20) 7679 5107

Email: stuart@xxxxxxxxxxxxxx

Home page: http://www.phon.ucl.ac.uk/home/stuart