As we know from everyday experience , “ a high reverberation time will cause a buildup of the noise level in the space … reverberation time [ is ] crucial to musical conditions and understanding speech ” ( Levy , 2012 ). In other words , we need to strike a balance and find a sweet spot in reverberation somewhere between the cacophony of a gymnasium and the sterile confines of a vocal booth . Too bad there isn ’ t a way to measure reverberation level scientifically …
RT TO THE RESCUE !
Oh , wait ! There is a way to measure reverberation time scientifically ! Actually , there are a few different subtle variations in the methodology , but we ’ ll stay fairly high level and pick one method here . Turning to Zuckerwar ( Encyclopedia of Physical Science and Technology , 2003 ) for the basic framework behind the scenes in one popular technique :
Reverberation time ( RT ) is the time required for the sound in a room to decay over a specific dynamic range , usually taken to be 60 dB , when a source is suddenly interrupted . The Sabine formula relates the RT to the properties of the room .
where V is the volume of the room , S the area of its surfaces , and α the absorption coefficient due to losses in the air and at the surfaces .
I know what you are thinking . “ I wasn ’ t told there would be math involved in this article !” Even if you aren ’ t following the specifics of the math , the concept is pretty simple . ( We ’ ll set aside the details on the math for the equivalent absorption surface for now , by the way .) The point here is that we can use the Sabine formula ( and related equations ) to derive a fairly apples-to-apples measurement for how reverberant a particular space is compared to another room . Sometimes referred to as ‘ RT60 ’ or ‘ RT30 ’, this calculation is how long it takes for a sound with a sound pressure level of 60 dB ( or 30dB , etc .) to die away . Turning back to that snare drum crack that took three seconds to dip below the threshold of human hearing , we could easily extrapolate the RT60 figure of the gym by measuring the room size and using this ‘ interrupted-noise ’ method to time the reverb trail .
Acousticians , architects , system technicians and audio engineers can use these figures to inform their approach to treating a room . Again , this isn ’ t a ‘ how-to ’ article , but rather a quick high-level pass through the general concept of RT to get us to the crux of the question here for worship audio scenarios . We know now that we can measure one room and compare it to another room when it comes to reverberation time . It isn ’ t a strictly subjective measure . So
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