Re: AUDITORY Digest - 14 Oct 2008 to 15 Oct 2008 (#2008-206)

[Jim Abbott <jfabbott@xxxxxxxxxxx>]

You might want to look at:

ANSI S12.35-1990. Precision Methods for the Determination of Sound  
Power Levels of Noise Sources in Anechoic and Hemi-Anechoic Rooms,  
Standards Secretariat, Acoustical Society of America, Melville, NY,  
1996.

or

ISO 3745. Acoustics - Determination of Sound Power Levels of Noise  
Sources - Precision Methods for Anechoic and Semi-Anechoic Rooms,  
International Organization for Standardization, Geneva, Switzerland,  
1977.

The basic criteria for usable working space in an anechoic chamber  
derive from two factors, both which depend strongly on frequency.   
The first is the need to be sufficiently far from the source to avoid  
near-field irregularities.  This distance depends on source size,  
shape, and frequency.  The other is the need to not work too close to  
the wedge tips.  This also depends on frequency, and can be based on  
staying some fraction of a wavelength away from the chamber's inner  
boundaries.

So, due to the need to be a certain distance from the source and also  
to avoid a "boundary layer" at the chamber perimeter, an experiment  
of a given size will quickly acquire a lower frequency limit-of- 
validity.  Other factors may be present, some at higher frequencies,  
but these two seem to be important ones to define a chamber's useable  
space an ad hoc lower frequency limit.

Best,

Dr. Jim Abbott
Cooper Union Audio Lab
The Cooper Union, 51 Astor Place, New York, NY 10003
(212)353-4002

On Oct 16, 2008, at 12:35 AM, AUDITORY automatic digest system wrote:

> There are 2 messages totalling 67 lines in this issue.
>
> Topics of the day:
>
>   1. accuracy of loudspeaker measurement in anechoic chamber:  
> dimension and
>      absorber (2)
>
> ----------------------------------------------------------------------
>
> Date:    Tue, 14 Oct 2008 23:37:32 -0700
> From:    Chuping Liu <tracy_liu_99@xxxxxxxxx>
> Subject: accuracy of loudspeaker measurement in anechoic chamber:  
> dimension and absorber
>
> Dear List,
>
> When loudspeaker is measured in anechoic chamber, for valid results  
> at low frequencies, it means large anechoic chamber and large  
> absorbent wedges. I found quite some literature discussing the  
> accuracy of loudspeaker measurement in terms of different wedges.  
> Yet I haven't found any literature talking about the measurement  
> accuracy (in terms of frequency extend and errors) regarding the  
> physical dimensions of the anechoic chamber, or ideally for both of  
> chamber dimensions and absorber characteristics.
>
> If anyone is aware of the existence of such literature, I would  
> appreciate to be pointed out. Thanks.
>
>
> Regards,
> Chuping
>
>
>
>
> ------------------------------
>
> Date:    Wed, 15 Oct 2008 22:16:56 +0100
> From:    Peter Lennox <P.Lennox@xxxxxxxxxxx>
> Subject: Re: accuracy of loudspeaker measurement in anechoic  
> chamber: dimension and absorber
>
> I've a feeling that the only people with such large anechoic rooms  
> will be =
> military, so whether their output is accesible, I don't know
> regards
> ppl
> Dr Peter Lennox
> Director of Signal Processing and Applications Research Group (SPARG)
> School of Technology,
> Faculty of Arts, design and Technology
> University of Derby, UK
> e: p.lennox@xxxxxxxxxxx
> t: 01332 593155
> w: http://sparg.derby.ac.uk/SPARG/Staff_PLX.asp
> ________________________________________
> From: AUDITORY - Research in Auditory Perception  
> [AUDITORY@xxxxxxxxxxxxxxx]=
>  On Behalf Of Chuping Liu [tracy_liu_99@xxxxxxxxx]
> Sent: 15 October 2008 07:37
> To: AUDITORY@xxxxxxxxxxxxxxx
> Subject: accuracy of loudspeaker measurement in anechoic chamber:  
> dimension=
>  and absorber
>
> Dear List,
>
> When loudspeaker is measured in anechoic chamber, for valid results  
> at low =
> frequencies, it means large anechoic chamber and large absorbent  
> wedges. I =
> found quite some literature discussing the accuracy of loudspeaker  
> measurem=
> ent in terms of different wedges. Yet I haven't found any  
> literature talkin=
> g about the measurement accuracy (in terms of frequency extend and  
> errors) =
> regarding the physical dimensions of the anechoic chamber, or  
> ideally for b=
> oth of chamber dimensions and absorber characteristics.
>
> If anyone is aware of the existence of such literature, I would  
> appreciate =
> to be pointed out. Thanks.
>
>
> Regards,
> Chuping
>
> ------------------------------
>
> End of AUDITORY Digest - 14 Oct 2008 to 15 Oct 2008 (#2008-206)
> ***************************************************************