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``````   OPTIMAL REVERBERATION TIME (Topt )
The optimal reverberation time, depending on the room volume (V) can be calculated using the following formulae, where Topt= Optimal time, lg=Logarithm and V = room volume in m3
WALLACE CLEMENT SABINE
(June 13, 1868 – January 10, 1919)
Wallace Clement Sabine was an American physicist who founded the field of architectural acoustics. He graduated from Ohio State University in 1886 at the age of 18 before joining Harvard University for graduate study and remaining as a faculty member. Sabine was acoustical architect of Boston’s Symphony Hall, widely considered one of the two or three best concert halls in the world for its acoustics. Sabine was able to determine, through his experiments, that a definitive relationship exists between the quality of the acoustics, the size of the chamber, and the amount of absorption surface present. He formally defined the reverberation time, which is still the most important characteristic currently in use for gauging the acoustical quality of a room, as number of seconds required for the intensity of the sound to drop from the starting level, by an amount of 60 dB (decibels).
His formula, if all units are SI (International System of Units), is:
Reverberation time RT60 =
k· V = 0.161 V AA
(V and A in meters)
with the factor k = (24 × ln 10) / c20 = 0.049 (feet) or withk=(24×ln10)/c20=0.161(meter)
RT60 = reverberation time in seconds (reverb time)
V = room volume in m
A = α × S = equivalent absorption surface or area in m2
α = absorption coefficient or attenuation coefficient The terms “attenuation coefficient” and “absorption coefficient” are used interchangeably
S = absorbing surface area in m2
A = α1 × S1 + α2 × S2 + α3 × S3 + ...
c20 = speed of sound is 343 m/s or 1126 ft/s at 20°C
--Wikipedia: Wallace Clement Sabine Retrieved August 6, 2013
See also http://www. sengpielaudio.com/ calculator- RT60.htm
THE ROOM’S PURPOSE
OPTIMAL REVERBERATION TIME
Talk: listening to news, talk shows, conversation
Topt=0.3lg V-0.05 ±10%
Music: Including musical theatre, studio recording
Topt=0.4lg V-0.15 ±10%
Symphonic music
Topt=0.5lg V-0.3 ±10%
The following formula (the Sabine formula) is used to calculate the standard reverberation time of a room:
.164V T= A
Where T = Time of reverberation
V= Volume of the room in m3, and
A=The total level of sound absorption the
room calculated on the principle of:
A = α1S1 + α2S2 + αnSn
αn = The sound absorption coefficient of n material
Sn = The surface area of n material α= The sound absorption coefficient
The sound absorption is the reduction of sound energy in the room that happens due to the loss of energy by sound waves upon reflection from surfaces in the room. The sound absorption coefficient is expressed as a ratio between reflected and absorbed sound energy. If this ratio has a value of “0”, for instance, there would be total sound reflection in
the room. A value of “1” corresponds to total sound absorption.
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