What is the Relation between sound power level and sound pressure level?

Answer 1

"Sound power" and "sound pressure" are two distinct and commonly confused characteristics of sound.

Sound power is the acoustical energy emitted by the sound source, and is an absolute value. It is not affected by the environment.

Sound power levels are connected to the sound source and are independent of distance. Sound power levels are indicated in decibels.

Lw = 10 log (W / Wo)

where:

The reference power is 10-12 watts (W), which is the lowest sound persons of excellent hearing can discern. Sound power is measured as the total sound power emitted by a source in all directions in watts (joules per second).

Since sound measuring instruments respond to sound pressure the "decibel" is generally associated with sound pressure level (SPL). Sound pressure levels quantify in decibels the intensity of given sound sources. Sound pressure levels vary substantially with distance from the source, and also diminish as a result of intervening obstacles and barriers, air absorption, wind and other factors. Sound pressure levels are indicated in decibels.

Sound pressure level (SPL) Lp = 20 log (p / po),

where:

The reference sound pressure is po = 2 x 10-5 pascals.

The usual reference level po is 20 x 10-6 pascals = 20 micropascals.

Sound pressure is a pressure disturbance in the air whose intensity is influenced not only by the strength of the source, but also by the surroundings and the distance from the source to the receiver. Sound pressure is what our ears hear and what sound pressure level meters (SPL meters) measure.