Sound power

  • Sound pressure
  • SPL
  • Sound velocity
  • Schallauslenkung
  • Sound acceleration
  • Sound intensity
  • Sound power
  • Sound energy density
  • Sound energy
  • Sonic flow
  • Acoustic impedance
  • Speed of sound

The sound power (symbol Pak ) a sound source is an acoustic size. It refers to the output per unit time from a sound source of sound energy. It is one of the sound energy sizes and is a mechanical performance. Your unit is watts ( W). The corresponding logarithmic size is the sound power level.

The sound power source describes the strength of a sound generator and not the sound field. Neglecting attenuation within the surrounding medium must therefore by any closed envelope to the sound source appear the same sound energy, regardless of their shape and distance to the sound source.

In the emission measurement, this is an important sound energy quantity for evaluation of a sound source, since the sound power of a noise source as opposed to the sound pressure, the sound velocity and the sound intensity is independent of the location of the source or the receiver.

The noise immission at a receiving can be calculated from the noise power when the sound power of the relevant at this location of sound sources, whose distance from the receiving point and the radiation are well known. So it is possible, for example, knowing the sound power levels of the individual components to determine the noise exposure of the operating personnel of a machine or even before its completion, and possibly initiate necessary mitigation measures.

Other than the sound pressure sound power is neither space nor dependent distance-dependent. The sound power belongs strictly to the sound source. The sound pressure is a measure of a point in space in the vicinity of the sound source, while the sound power is the total power radiated from the sound source in all directions ( emitted ).

Definition

Is an imaginary envelope surface A selected so that the sound intensity is uniformly distributed over the envelope surface and is in each case oriented perpendicularly to the envelope surface, one obtains the noise power as the product of the sound intensity I and the area A, or as the product of the sound pressure p, the sound velocity v and echoed through the area A.

The sound power can be determined v a by echoing area A also by integrating the sound intensity I a by echoing area A or from the integral of the product of acoustic pressure p and acoustic particle velocity, wherein for each patch only the directed perpendicular to the surface components of sound intensity and sound velocity have an influence on the determination of the sound power. Mathematically, this relationship of the scalar product of a sound intensity or sound velocity vector to a vector area, wherein the area vector is oriented perpendicular to the respective surface portion.

Sound power level

Often referred to as an indication of the sound power is the sound power level LW in decibels ( dB):

With the standard for airborne sound reference value P0 = 10-12 W.

Measurement

General

Is (e.g., for Emission ) emitted by a sound source sound power can be determined, the area A will be chosen so that the total sound source will be wrapped and on the envelope surface of the sound field is measured. It does not matter at what distance from the sound source is located in this envelope. ( In extremely rare individual cases recorded by a sound receiver noise power is determined, then the area A is chosen so that all paths are recorded at the receiver, by the ear, for example, the ear canal area. )

To measure the radiated sound power of a noise source, there are several methods of measurement:

  • Measurement in an anechoic chamber with sides anechoic lining: measurements over the entire envelope of the sound source (only possible for hanging sound sources ).
  • Measuring in an anechoic chamber half ( solid, reverberant ground anechoic walls ) measurements on an envelope of the above base ( for example in heavy noise sources ).
  • Measurements in a reverberation chamber: Since here a diffuse field is formed in which, ideally, everywhere there is the same sound pressure, may, after calibration of the space theory of a single sound pressure measurement, the acoustic power of the sound source can be determined ( with a source of known sound power or by measuring the reverberation time ).
  • In any environment with ambient noise or reflections: this must be measured to determine the sound power passing through an enveloping surface to the source of sound intensity. This measurement captures both the radiated outward sound, as well as by the radiating through the enveloped volume of background noise. This can thus be eliminated.

Can be used to measure the sound power, therefore, sound intensity probes or microphones (which are actually really sound pressure receiver). Microphones provide, however, only a correct result when the sound occurs everywhere perpendicularly through the envelope and no background noise is present.

Most of the emitted sound power is given in the form of sound power level.

The emitted sound power of a noise source is independent of location and space independently. It is the same for all distances from the sound source. Specifying a distance creates only confusion here. Often, the location-independent sound power level is confounded with the position-dependent sound pressure level ( SPL), because both levels are expressed in dB.

Determination of sound pressure according to DIN EN ISO 3746:2011-03

The starting point is the measurement of the sound pressure level at specified positions of a envelope. Details of these positions can be found in the above standard or in an appropriate product standard.

The starting point is the measurement of sound pressure levels, of which the average value

Is determined. When correction factors is called the norm of the residual noise correction factor and the influence of the measurement environment which can be calculated measuring surface sound pressure level. The sound power level is so

With

With obtained. Thus, with the same medium, the sound pressure of sound power is larger when the sound pressure over a larger area was measured.

Table: Sound power level and sound power level of various sound sources

The music of a trumpet and the construction noise by an excavator have about the same sound power, but are evaluated psychoacoustically completely different.

Sound power in a plane sound waves

Following relationship exists between the sound power in plane progressive sound waves and other important acoustic quantities:

Where:

38945
de