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cover page : experiment title, name
abstract: describe the experiment. in your own words in a short paragraph.
procedure: describe what was done (only key points)
analysis : (answer the questions that are attached)
conclusion: mention how well the experiment supports the theory being tested.
language: write in format English past tense, passive voice. avoid terms like, I, we, he ,she
REVERBERATION TIME PURPOSE
To understand how to calculate the reverberation time for a room.
THEORY
Reverberation is the combined effect of multiple sound reflections in a room which result to a gradual decay of the sound heard by the listener after the source of sound stops.
In order to deal with this effect in a quantitative way, the concept of reverberation time TR is used. TR is defined to be the time it takes for the sound to drop by 60dB from its steady state value after the sound is turned off. The reverberation time depends on the size and shape of the room as well as its contents.
A rather simple, approximate formula for the reverberation time in seconds is
where V is the volume of the enclosure in ft3(V=length x width x height) and A is
2 the total absorption of the surface of the room (or area) in ft .
If the areas and volumes are measured in terms of meters rather than feet, the coefficient 0.05 is replaced by 0.161 in the formula above.
The total absorption A (measured in sabins) is
=∑ = 1 1+ 2 2+ 3 3+⋯
where Si are the surface area of various materials (measured in ft2) in the enclosure, and ai are their respective absorption coefficients per square feet. (measured in sabins/ ft2).
= 0.05
Table 1: Absorption coefficients (sabins/ft2) for some common materials found in studios or concert halls. Note that the absorption coefficients are frequency dependent.
Table 2: Absorption (per unit) of seating arrangements with different states of upholstery and occupancy.
Figure 1: Ideal average reverberation time versus room volume for different types of rooms, including rooms that are specific to different types of music.
SCENARIO
The ceiling is made of acoustical boards. The floor is carpeted. The long side walls are made of brick and there are 20 glass windows overall, each of size 3ft x 6ft. The entrance wall has a glass door of size 12ft x 7ft. The rest of the entrance wall as well as the back wall are also made of brick. The room also contains 400 upholstered seats.
Floor (plywood)
Figure 2: Dimensions and details of the scenario described above QUESTIONS
1. Calculate the reverberation time for this hall for f = 500Hz, when the seats are unoccupied, and when they are occupied.
2. For which purposes might this room be suited?
3. If you wanted to have a longer TR, how would you redesign the hall interior?
4. A room with a volume of 10,000 ft2 has TR = l.5 s. What is the total absorption of the
room surface?
5. Calculate the frequencies of the first few standing waves in a bathroom stall that is 1.5 m
wide, 2.5 m long and 3.0 m high. Draw a frequency (Fourier) spectrum for your findings, with equal relative amplitudes for all frequencies present. Hint: treat the bathroom stall as a tube closed at both ends with the above dimensions.
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