Pat,
That is indeed the case, but since the variables are volume divided by
area (the latter adjusted by absorption coefficients), one must change
the equation's coefficient. The nonmetric version uses 0.0485 s/ft (I
have also seen 0.049 s/ft used) and the metric version uses 0.16 s/m (I
have also seen 0.161 s/m and 0.163 s/m used).
The effect of the absorption coefficients is to convert actual areas
into equivalent areas of perfect absorbers. This Sabin equation is the
simplified form for diffuse sound and does not take into account other
factors such as air absorption, which should be done for very large
rooms. Other forms of the equation include some of the more subtle
factors. None of them allow for resonance effects which are promoted by
parallel surfaces; these must be accounted for separately.
Jim
On Friday 30 March 2001 2300, Pat Naughtin wrote:
> Dear Karl, and All,
>
> The Dent Dictionary of Measurement lists two entries that might be
> relevant to your request. Both the unit and the formula were named
> for the American physicist Wallace Sabine (1868-1919).
>
> 'sabin
> [physics] Obsolete unit of sound absorption (by architectural
> materials), equal to the absorption of an open window of 1 square
> foot area (0.0929 square metre) for low frequency sound waves. (The
> absorption of an open window was assumed to be total, or perfect.'
>
> 'Sabine reverberation formula
> [physics] For an enclosure, the reverberation time of a sound equals
> 0.16 times the volume (in cubic metres) divided by the total
> absorption in the enclosure (that is, the product of the absorption
> coefficient and the surface area in square metres).'
>
> It seems to me that the 'absorption coefficient' would be a
> dimensionless coefficient that technically would not have a unit, but
> someone has given it the name sabin to honor Wallace Sabine. I
> suppose it's a bit like radians and steradians, which are both ratios
> that technically don't need unit names.
>
> My guess would be that we could think of an anechoic chamber as
> having an absorption coefficient of say 0.98; and we could call this
> 0.98 sabin. On the other hand if we designed a strongly reverberant
> room, it might have an absorption coefficient of something like 0.1;
> and we could call this 0.1 sabin.
>
> If my guess is correct then you could use the sabin number as the
> absorption coefficient is SI as it was in ifp units - just ignore the
> unit altogether.
>
> Cheers,
>
> Pat Naughtin CAMS
> Geelong, Australia
>
> on 2001/03/31 02.48, Karl G. Ruling at [EMAIL PROTECTED] wrote:
> > Does anyone know the SI or metric equivalent of the sabine? The
> > sabine is the unit of sound absorbtion of one square foot of a
> > perfect sound absorber (an open window, e.g.). I can't find the
> > sabine listed in IEEE/ASTM SI 10 or in the NIST guide.
> > Best regards,
> > Karl G. Ruling
> > Technical Standards Manager
> >
> > The Entertainment Services & Technology Association
> > 875 Sixth Avenue, Suite 2302
> > New York, NY 10001
> > +1-212-244-1505
> > Fax: +1-212-244-1502
--
James R. Frysinger University/College of Charleston
10 Captiva Row Dept. of Physics and Astronomy
Charleston, SC 29407 66 George Street
843.225.0805 Charleston, SC 29424
http://www.cofc.edu/~frysingj [EMAIL PROTECTED]
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