Sound power : is the total airborne sound energy radiated by a sound source per unit of time. the sound power, which is continuously emitted from a sound source.
Sound pressure : is the result of sound sources radiating sound energy that is transferred into a specific acoustical environment and measured at a specific location.
Sound power is the cause, and sound pressure is the effect.
The sound pressure levels will depend on our distance from the source and the characteristics of the room.
This includes the size of the room, and how much the surfaces within the room reflect or absorb sound.
LW= sound power level (dB) , LP =Sound Pressure Levels (dB)
LWA= A-weighted sound power level (dB), LI= sound intensity level
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Conversion of Sound Power Level to Sound Level
LW = sound power(db)
r = Distance to sound source r meter
Q= Directivity factor
Conversion of Sound Level to Sound Power Level
Sound Attenuation Calculator - Inverse Square Law
The formula to calculate sound attenuation over distance for a point source is:
Lp(R2) = Lp(R1) - 20·Log10(R2/R1)
Where:
Lp(R1) = Known sound pressure level at the first location (typically measured data or
equipment vendor data)
Lp(R2) = Unknown sound pressure level at the second location Location
R1 = Distance from the noise source to location of known sound pressure level
R2 = Distance from noise source to the second location
According to DIN 45635, Teil 38, or ISO 13347-3 in accordance with the described enveloping surface, where through a rectangular measuring surface several measuring points were seized.
Typical Subjective Description of Sound Pressure Level
0 - 40 dB : quiet to very quiet
60 - 80 dB : noisy
100 dB : very noisy
> 120 dB : intolerable
Note :
For lowest noise output, fans should always be operated near their peak efficiency point. A common mistake is to use a fan that is too small (or too large) for the application, so that it cannot be run at its most efficient point. A better way from a noise standpoint (but more expensive), is a variable speed motor drive.
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