Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 428

where
L w = Sound power level (decibels).
w = Sound power (watts).
w 0 = Reference power (10 -12 watts).
log 10 = Logarithm to the base 10.

15.7.5.2 Sound Pressure
Units used to describe sound pressures are

1 µbar = 1 dyne/cm 2 = 0.1 N/cm 2 = 0.1 Pa

15.7.5.3 Sound Pressure Level

SPL = 10 log( p 2 / p 0 )

where
SPL = Sound pressure level (decibels)
p = Measured rms sound pressure (N/m 2 , µba rs). *
p 0 = Reference rms sound pressure (20 µPa, N/m 2 , µba rs)

15.7.5.4 Speed of Sound

c = f λ

15.7.5.5 Wavelength

λ = c / f

15.7.5.6 Frequency of Octave Bands

Upper frequency band = f 2 = 2 f 1

where
f 2 = Upper frequency band.
f 1 = Lower frequency band.

One-half octave band == f 2 f

2 1

where
f 2 = 1/2 octave band.
f 1 = Lower frequency band.

One-thirdoctaveband == f

3 2

f

2 1

where
f 2 = 1/3 octave band
f 1 = Lower frequency band

* The root-mean-square (rms) value of a changing quantity, such as sound pressure, is the square root of the mean of the
squares of the instantaneous values of the quantity.