m made first instance of "sound pressure" a link because it is closely related to sound power
|
No edit summary
Tags: Mobile edit Mobile web edit
|
||
Line 1: | Line 1: | ||
{{Refimprove|date=October 2008}} |
{{Refimprove|date=October 2008}} |
||
{{Sound |
{{Sound hai |
||
Ymeasurements}} |
|||
'''Sound power''' or '''acoustic power''' is the rate at which [[sound energy]] is emitted, reflected, transmitted or received, per unit time.<ref name=clinical>{{cite book|url=https://books.google.com/books?id=ElPyvaJbDiwC&pg=PA94&dq=sound+power+loudness&hl=en&sa=X&ei=YF0XVdbsEpOBNoeFgKgN&ved=0CCcQ6AEwAA#v=onepage&q=sound%20power%20loudness&f=false|title=Clinical Measurement of Speech and Voice|author=Ronald J. Baken, Robert F. Orlikoff|publisher=Cengage Learning|year=2000|isbn=9781565938694|page=94}}</ref> The [[International System of Units|SI unit]] of sound power is the [[watt]] (W).<ref name=clinical/> It is the power of the sound force on a surface of the medium of propagation of the sound wave. For a sound source, unlike [[sound pressure]], sound power is neither room-dependent nor distance-dependent. Sound pressure is a property of the field at a point in space, while sound power is a property of a sound source, equal to the total power emitted by that source in all directions. Sound power passing through an area is sometimes called '''sound flux''' or '''acoustic flux''' through that area. |
'''Sound power''' or '''acoustic power''' is the rate at which [[sound energy]] is emitted, reflected, transmitted or received, per unit time.<ref name=clinical>{{cite book|url=https://books.google.com/books?id=ElPyvaJbDiwC&pg=PA94&dq=sound+power+loudness&hl=en&sa=X&ei=YF0XVdbsEpOBNoeFgKgN&ved=0CCcQ6AEwAA#v=onepage&q=sound%20power%20loudness&f=false|title=Clinical Measurement of Speech and Voice|author=Ronald J. Baken, Robert F. Orlikoff|publisher=Cengage Learning|year=2000|isbn=9781565938694|page=94}}</ref> The [[International System of Units|SI unit]] of sound power is the [[watt]] (W).<ref name=clinical/> It is the power of the sound force on a surface of the medium of propagation of the sound wave. For a sound source, unlike [[sound pressure]], sound power is neither room-dependent nor distance-dependent. Sound pressure is a property of the field at a point in space, while sound power is a property of a sound source, equal to the total power emitted by that source in all directions. Sound power passing through an area is sometimes called '''sound flux''' or '''acoustic flux''' through that area. |
This article needs additional citations for verification. Please help improve this articlebyadding citations to reliable sources. Unsourced material may be challenged and removed.
Find sources: "Sound power" – news · newspapers · books · scholar · JSTOR (October 2008) (Learn how and when to remove this message) |
{{Sound hai Ymeasurements}}
Sound poweroracoustic power is the rate at which sound energy is emitted, reflected, transmitted or received, per unit time.[1] The SI unit of sound power is the watt (W).[1] It is the power of the sound force on a surface of the medium of propagation of the sound wave. For a sound source, unlike sound pressure, sound power is neither room-dependent nor distance-dependent. Sound pressure is a property of the field at a point in space, while sound power is a property of a sound source, equal to the total power emitted by that source in all directions. Sound power passing through an area is sometimes called sound fluxoracoustic flux through that area.
Regulations[3] control the maximum sound power level LWA that a device (e.g. vacuum cleaner) is allowed to produce. The A-weighting scale is used in the calculation as the regulation is concerned with the loudness as perceived by the human ear. Measurements[4] are taken at several defined points around the device.
The test environment can be located indoors or outdoors. The ideal environment is on the ground in a large open space or hemi-anechoic chamber (free-field over a reflecting plane ). To account for undesired reflections from nearby objects, walls, and the ceiling, and for any residual background noises, measurement corrections are applied.
Here is a table of some examples.[5]
Situation and sound source |
Sound power (W) |
Sound power level (dB ref 10−12W) |
---|---|---|
Saturn V rocket | 100,000,000 | 200 |
Project Artemis Sonar | 1,000,000 | 180 |
Turbojet engine | 100,000 | 170 |
Turbofan aircraft at take-off | 1,000 | 150 |
Turboprop aircraft at take-off | 100 | 140 |
Machine gun Large pipe organ |
10 | 130 |
Symphony orchestra Heavy thunder Sonic boom |
1 | 120 |
Rock concert Chain saw Accelerating motorcycle |
0.1 | 110 |
Lawn mower Car at highway speed Subway steel wheels |
0.01 | 100 |
Large diesel vehicle | 0.001 | 90 |
Loud alarm clock | 0.0001 | 80 |
Relatively quiet vacuum cleaner | 10−5 | 70 |
Hair dryer | 10−6 | 60 |
Radio or TV | 10−7 | 50 |
Refrigerator Low voice |
10−8 | 40 |
Quiet conversation | 10−9 | 30 |
Whisper of one person Wristwatch ticking |
10−10 | 20 |
Human breath of one person | 10−11 | 10 |
Reference value | 10−12 | 0 |
Sound power, denoted P, is defined by[6]
where
In a medium, the sound power is given by
where
For example, a sound at SPL = 85 dB or p = 0.356 Pa in air (ρ = 1.2 kg·m−3 and c = 343 m·s−1) through a surface of area A = 1 m2 normal to the direction of propagation (θ = 0 °) has a sound energy flux P = 0.3 mW.
This is the parameter one would be interested in when converting noise back into usable energy, along with any losses in the capturing device.
Sound power is related to sound intensity:
where
Sound power is related sound energy density:
where
Sound power level (SWL) or acoustic power level is a logarithmic measure of the power of a sound relative to a reference value.
Sound power level, denoted LW and measured in dB, is defined by[7]
where
The commonly used reference sound power in air is[8]
The proper notations for sound power level using this reference are LW/(1 pW)orLW (re 1 pW), but the suffix notations dB SWL, dB(SWL), dBSWL, or dBSWL are very common, even if they are not accepted by the SI.[9]
The reference sound power P0 is defined as the sound power with the reference sound intensity I0 = 1 pW/m2 passing through a surface of area A0 = 1 m2:
hence the reference value P0 = 1 pW.
The generic calculation of sound power from sound pressure is as follows:
where:
defines the area of a surface that wholly encompasses the source. This surface may be any shape, but it must fully enclose the source.
In the case of a sound source located in free field positioned over a reflecting plane (i.e. the ground), in air at ambient temperature, the sound power level at distance r from the sound source is approximately related to sound pressure level (SPL) by[10]
where
Derivation of this equation:
For a progressive spherical wave,
where z0 is the characteristic specific acoustic impedance.
Consequently,
and since by definition I0 = p02/z0, where p0 = 20 μPa is the reference sound pressure,
The sound power estimated practically does not depend on distance. The sound pressure used in the calculation may be affected by distance due to viscous effects in the propagation of sound unless this is accounted for.