Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 224

9.2.1.8 Sound Pressure

Sound pressure or acoustic pressure is the deviation from ambient atmospheric
pressure caused by a sound wave. The SI unit of sound pressure, p , is the pascal (Pa).
ApascalPa

N/m 2 s 2 Newton, that is, the force that

produces an acceleration of 1 m/s when exerted on a mass of 1 kg). Considering
that the smallest audible sound pressure in air is of order of 10 6 Pa, sound pressure is
usually expressed in

¼ 1 ¼ 1 kg/m (N ¼

μ Pa.

9.2.1.9 Sound Pressure Level

Sound pressure level (SPL) or sound level ( L p ) is a logarithmic measure of the
effective sound pressure of a sound relative to a reference value. It is measured in
decibels (dB) above a standard reference level. The commonly used “zero” refer-
ence sound pressure in air is 20

μ Pa RMS, which is usually considered the threshold

of human hearing (at 1 kHz).

dB

P
P ref

L p ¼ 20 log 10

In water this reference pressure ¼ 1 μ Pa.

9.2.1.10 Sound Power

Sound power or acoustic power, P ac , is a measure of sonic energy per time t unit
P ac ¼ unit area.

The unit of measurement for power is the watt (W): 1 W

I A , where I ¼ sound intensity and A ¼

¼ 1 N of work per

second .

9.2.1.11 Sound Power Level

The sound power level (SWL, Lw, L p ac ) is the difference between two P ac expressed
in dB according the formula

dB

P 1
P 0

Lw ¼ 10 log 10

9.2.1.12 Sound Intensity

Sound intensity or acoustic intensity ( I ) is defined as the sound power , P ac , (ac ¼

acoustic) per unit area A : I ¼ P ac / A.