10 Years ago in Bandworld
Is Your Rehearsal Room Safe?
by Lee Ponder
Vol.17 , #5, p.8 (May - July 2002)
Before we can begin to solve acoustical problems in our rehearsal halls we need to understand how we are being physically damaged by them. There are standards for sound levels established by the United States Department of Labor Occupational Safety and Health Administration (OSHA) which can give us some guidelines as to what are safe levels of sound.
The standards for damage to hearing vary from country to country. In the USA, OSHA standards are that 90 decibels for eight hours a day will not cause damage (see chart below); 95 decibels should only be endured for four hours, 100 decibels for two hours, 105 decibels for one hour, 110 decibels for thirty minutes, 115 for fifteen minutes 120 for seven and a half minutes. Above 120 decibels will cause damage almost immediately.
Duration in Hours Sound Level In Decibels
.25 or less 115
For those not sure just what a decibel is, here is a paraphrase from The Acoustical Foundations of Music: One decibel may be defined as a barely discernible sound while one hundred twenty decibels is our pain threshold. An increase of three decibels doubles the sound pressure we experience. Decibel measurements are logarithmic in nature.
In order to get some rough data on sound levels music educators endure, I purchased a decibel meter from Radio Shack ($30.00). Some results are:
Jazz Ensemble 15 players 115 db
Brass Class 18 players 110 db
Marching Band 100 players 115-120 db
It is true that the above samples do not usually persist at these levels, but they go on for periods of two minutes or more and those periods are repeated many times. For comparison consider a recent performance of Mahler’s Sixth Symphony by the Chicago Symphony Orchestra. Usually thought of as a very powerful ensemble, this performance in Orchestra Hall in Chicago rarely exceeded 85 db as measured from the audience.
The three samples above were constant in most parts of a room which is fifty-two feet by sixty-two feet long with a fourteen-foot high suspended ceiling. While the two side walls are slanted for sound dispersion, the front wall is the only wall with acoustical absorption material attached. There is a thin carpet without any pad glued to the concrete floor.