DAMPA_75_years_of_quiet_design_ENG - Flipbook - Page 20
Modern room
acoustics
The development of practical acoustics first began in the
mid-1890s when the American physicist Wallace Clement
Sabine, a young Professor of Physics at Harvard University,
successfully applied scientific analysis to improve the
soundscape of an acoustically problematic lecture hall in the
University’s recently-completed Fogg Museum. Through
numerous experiments using cushions and rugs, Sabine
was able to prove a clear relationship between acoustical
quality and the amount of absorptive surface area within a
space.
He also defined the reverberation time – which is the most
important measure of the acoustical quality of a space – as
the number of seconds required for the intensity of a sound
to drop by 60 decibels from its starting level. For room
acoustics, the key frequencies are usually the speech frequencies – the 500 Hertz, 1000 Hertz and 2000 Hertz
octaves.
Sabine determined that the optimal reverberation time for a
lecture hall was just less than one second, but for a concert
hall it should be just over two seconds to avoid music
sounding too ‘dry’. The Fogg Museum’s reverberation time
was found to be five-and-a-half seconds, during which a
speaker could utter as many as fifteen more words, which
would be inaudible due to the large amount of resonance
and echo.
By adding absorptive materials throughout the space,
Sabine succeeded in drastically reducing the reverberation
time and removing the consequent echo effect. Later, he
was hired to provide guidance for the design of Boston’s
Symphony Hall, completed in 1900 and widely regarded as
among the world’s best. The unit of sound absorption, the
Sabin, was named in his honour.
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