ACOUSTICS TECHNOLOGY
NOISE CONTROL
1. SOUND ✰ A pressure wave ✩
Sound is a vibration in an elastic_2. NOISE ✩ Unwanted sound ✩ medium. The media of interest are air and building materials.
SOUND
LEVEL METER
4. SOUND LEVEL Measure of
✩ sound pressure - as recorded by a sound level meter in db.
70db
The most beautiful sounds if un- wanted are distracting noise.
5.
dba
"A" WEIGHTED SOUND LEVEL (dba) Measurement scale on the sound level meter, recording approximately what the human ear hears.
Mw
3. DECIBEL (db) ✩ A unit of sound intensity measurement ✩ Inside your home the ambient sound level should be no more than 40 db. Inside the cabin of a jet it will be 80-90 db.
АААА
6. FREQUENCY ✩ The pitch of sound Frequency is the number of vibrations per second and is measured in cycles per second (CPS). The greater the number of cycles per second, the higher the pitch of the sound.
LISTENER
PATH
SOURCE
40 db TL
30db
7. TRANSMISSION LOSS Iso- lating effectiveness ✩ The trans- mission loss (TL) of a wall or floor is the number of decibels by which the level of airborne sound is decreased in passing through the structure. Transmis- sion loss is invariably greater for high frequencies than low.
8. VIBRATION ISOLATION ✩ Prevention of vibration from a vibrating source to its supporting
structure.
ROOM ACOUSTICS
PATH
9. THE SYSTEM There are three basic parts to any noise con- trol problem: the noise source, transmission paths and listener.
R.T. (reverberation time)
10. ABSORPTION COEFFI- CIENT ✩ A measure of absorp- tion, where the absorption is the conversion of sound to heat The value of the coefficient falls be- "O" for no absorption
tween
(total reflection) and “1” (total absorption). The absorption of a material changes with frequency. "Acoustical materials" absorbing ability varies with method of application.
11. REVERBRATION ✩ Remain- ing sound in an enclosed space after source has been switched off
The time it takes for the sound to decay can be controlled by absorption and reflection of the room surfaces.
Far East BUILDER, July 1970
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