7-6 Quantitative Acoustical Parameters
What is the reverberation time?
The reverberation time includes:
- How rapidly the reflected waves decay
- The time required for the intensity to decrease by a factor of one million
- The time required for the sound intensity to decrease to 60 db
How do you find the reverberation time?
The reverberation time is shown on a sound decay curve, such as the ones below:
These graphs show a steady decline in sound intensity as time passes.
However, in actuality most reverberation graphs will look more like this:
The sound intensity will decrease until it reaches a certain point where it will level off.
Rt = (0.16V) / (A + AaV)
where Rt is the reverberation time
where V is the volume of the enclosure in m^3, A is the total absorption in m^2 sabians, and Aa is the absorption coefficient of air
An audience will increase the total absorption and therefore decrease the reverberation time (especially if they have heavy coats on).
What is the initial-time-delay group?
The initial-time-delay is the interval of time between the perception of the direct sound and the perception of the first reflected sound.
How do you find the initial-time-delay?
The initial-time-delay is found with the following formula:
tp = Rp / V
tr = (R1 + R2) / V
ti = tr - td = (R1 + R2 - Rp) / v = (R1 + R2 - Rd) / 345
Practice Problems:
1. Calculate the reverberation time of a 5 m X 5 m X 5 m room. The volume of the room is 100 m^3 and the total absorption is 7.10 sabians. Do not consider the absorption of air in your response.
2. Calculate the reverberation time of the room above taking into account the absorption of air. Assume that there is a humidity of 50% and use the absorption coefficient of air for a frequency of 2,000 Hz.
Continue: #REDIRECT 7-7 Solving Acoustic Problems
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