DAMPA whitepaper acoustics - Flipbook - Page 5
The reverberation time is thus the key factor when assessing acoustics.
If the reverberation time is long, sound turns into noise because sound waves from
the same source reach us multiple times.
For example, in a room with a long reverberation time, spoken words do not fade
before new ones reach the listener. This causes speech to blur, as sound reflections
prolong the reverberation.
Reverberation time is measured in seconds - the time it takes for sound to decrease by 60 dB after the sound source
has stopped. This is the key parameter when evaluating and optimising room acoustics.
Why Does Long Reverberation Times Occur?
A long reverberation time occurs when there isn’t enough sound-absorbing material in a room. Without proper absorption, sound waves are free to bounce off surfaces instead of being dampened, causing prolonged reflections and
echo.
From a technical perspective, we look at the absorption coefficient, denoted as alpha (α). Ideally, a
sound-absorbing material should have an alpha value
of 1, meaning it absorbs 100% of the sound.
When α = 1, no sound is reflected back into the room,
preventing prolonged reverberation.
Sound is absorbed by the soundabsorbing material.
Sound is reflected by the hard
surface.
Logically, one might assume that the closer an absorber’s alpha value is to 1, the fewer elements are needed to reduce the reverberation time.
This is true, to some extent.
However, effective acoustic optimization also depends on the placement of absorping elements and the intended use
of the space.
It is through this balance that reverberation time can be properly controlled, creating rooms with optimal acoustics.
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