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TRG-TRC007-EN 13
period one
Fundamentals of Sound
notes
When a reference value is established and placed in the denominator of the
ratio, the dB can be calculated for any value entered into the numerator.
The reference value used for calculating sound-power level is 1 picowatt (pW),
or 10
-12
watts. Therefore, sound-power level (L
w
) in dB is calculated using the
following equation:
The reference value used for calculating sound-pressure level is 20
micropascals (µPa), or 2 ×10
-5
Pa. Therefore, sound-pressure level (L
p
) in dB,
is calculated using the following equation:
Equation for Sound Power
sound power, W
10
-12
W
L
w
= 10 log
10
Figure 15
L
W
10 log
10
sound power, watts
10
-12
watts
------------------------------------------------------- -
=
Equation for Sound Pressure
sound pressure, m
mm
mPa
20 m
mm
mPa
L
p
= 20 log
10
Figure 16