Sound power level

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Sound measurements
Sound pressure p
Sound pressure level (SPL)
Particle velocity v
Particle velocity level (SVL)
(Sound velocity level)
Particle displacement ξ
Sound intensity I
Sound intensity level (SIL)
Sound power P_ac
Sound power level (SWL)
Sound energy density E
Sound energy flux q
Acoustic impedance Z
Speed of sound c

Sound power level or acoustic power level is a logarithmic measure of the sound power in comparison to a specified reference level.

The measure of a ratio of two sound powers is <ref>Sound Power, Sound Intensity, and the difference between the two - Indiana University's High Energy Physics Department</ref> <ref>Georgia State University Physics Department - Tutorial on Sound Intensity</ref>

<math>

L_\mathrm{W}=10\, \log_{10}\left(\frac{W_1}{W_0}\right)\ \mathrm{dB} </math>

where W₁ and W₀ are the powers.

The sound power level is given the symbol L_w or SWL and is measured in "dBW", which stands for decibel with the suffix for watts. Decibels are dimensionless. SPL stands for sound pressure level, and is not the same thing.

If W₀ is the standard reference sound power, where

<math>

W_0=10^{-12}\ \mathrm{W} </math>

(W = watt), then instead of "dB", dB SWL is used. (SWL = sound power level).

[edit] Table: Sound power level and sound power of some sound sources

Situation and sound source	sound power P_ac watts	sound power level L_w dB re 10^-12 W
Rocket engine	1,000,000 W	180 dB
Turbojet engine	10,000 W	160 dB
Siren	1,000 W	150 dB
Heavy truck engine or loudspeaker rock concert	100 W	140 dB
Machine gun	10 W	130 dB
Jackhammer	1 W	120 dB
Excavator, trumpet	0.3 W	115 dB
Chain saw	0.1 W	110 dB
Helicopter	0.01 W	100 dB
Loud speech, vivid children	0.001 W	90 dB
Usual talking, Typewriter	10⁻⁵ W	70 dB
Refrigerator	10⁻⁷ W	50 dB
(Auditory threshold)	10^-12 W	0 dB

The Trumpet and excavator both have the same sound power of 0.3 watts, but may be judged psychoacoustically to be different levels. As noise is unwanted sound the trumpet can be perceived to be acceptable when listened to as music but at the same sound power level may be perceived to be noisy if one is trying to sleep.

One of the advantages of expressing the noise level of a source in terms of its power level is that one does not have to note any distance from the source. A noise sound pressure level, say, 85 dB-A is meaningless unless one also notes the distance from the source where the measurement was made.de:Schallleistungspegel es:Nivel de potencia acústica