Absorbing Sound

We have already discussed reducing transmission of sound, to stop noise from entering a space.  When sound enters a space, or originates in that space, its behavior is affected by the room finishes. If the room has all hard surfaces (sound reflecting), this will make the room more “reverberant” and sound level in the room can build up due to reflections. Softer surfaces such as acoustic ceiling, wall panel treatments, and carpeting, can reduce reverberation of sound and will increase the intelligibility of speech.

Acoustical panels on walls and acoustical ceiling tiles can be very effective at reducing reverberation and noise.

Note that good sound absorbing materials such as fiberglass typically are not very good as sound barriers, and good sound barriers such as gypsum wall board are not good sound absorbers. The layering of the two in tandem is an effective solution to achieve both goals, or for noise reduction between spaces.

Reverberation time  is a measure of the time in seconds it takes for an impulse of sound such as a loud hard clap to decay by 60 dB (become inaudible) in a space. Lower reverberation time yields better speech intelligibility by minimizing the audible blurring of individual speech sounds due to multiple strong reflections (i.e. – reverberation).

Table Y: Maximum acceptable reverberation time  in unoccupied, furnished learning spaces. Note that a lower time increases the speech intelligibility in a room.

INsert chart here (from below)

Note (a) Reverberation times in octave bands with midband frequencies of 500, 1000, and 2000 Hz.

Note (b) Core learning spaces ≤ 283m³(≤ 10,000 ft ³ ) shall be readily adaptable to allow reduction in reverberation time to 0.3 sec.  (Lou, what is this from?)

Learning Space	Maximum Reverberation Time(a) (seconds)
Core learning space with enclosed volume ≤283m3  (≤ 10,000 ft3) Core learning space with enclosed volume >283m3 and ≤ 566 m3 (> 10,000 ft3 and ≤ 20,000 ft3) Core learning space with enclosed volume >566 m3 (> 20,000 ft3) and all ancillary spaces	0.6(b) 0.7 no requirement

this sound wave picture got dissed in the review--it will need a caption or get tossed. Not sure if it has a place in the absorption section-- PP please comment on the selection. should we have a representation of a diminished sound wave due to an absorptive surface? -Dave

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