
259Noise
Sound pressure: Dynamic variation in atmospheric
pressure. The pressure at a point in space minus
the static pressure at that point.
Sound pressure level: Fundamental measure of sound
pressure dened as
L
p
= 20
lo
B
where
P is the RMS value (unless otherwise stated)
of sound pressure in units of Pascals
P
0
is 1 μPa
Sound transmission loss: Ratio of the sound energy
emitted by an acoustical material or structure
to the energy incident upon the opposite side.
Standing wave: A periodic wave having a xed distri-
bution in space that is the result of interference
of progressive waves of the same frequency and
kind; characterized by the exi