Sound Power Analysis Object and Template (Acoustics Option)
This analysis object allows you to determine the sound power according to international standards. The level signals of several microphones are averaged energetically and a number of correction terms for barometric pressure, temperature, background noise, environmental correction and size of the measuring surface are considered.
To determine the sound power, an enveloping surface is assumed around the test object, and microphones are placed at several points on this enveloping surface. The required number of microphones depends on the standard to be observed and the precision grade requested and is usually between 6 and 10. The signals of these microphones are captured simultaneously or, in the case of time-invariable noise, one after the other. The measuring surface sound pressure level is the energetic average of the sound pressure levels of these microphones while considering the correction terms K0, K1 and K2. The sound power level is the sum of measuring surface sound pressure level and measuring surface dimension Lss.
Data
The analysis object can process three different data structures. You can specify a level signal as inputs for each of the microphones placed on the enveloping surface. You can obtain the level signals e. g. from the analysis object Sound Level. Please make sure that all level signals have the same length and frequency weighting.
Alternatively, you can also specify a data series with levels for every microphone. Please make sure that all data series have the same length and that all levels have the same frequency weighting.
As a third alternative, you can also specify Levels as scalar values for every microphone. Please make sure that all levels have the same frequency weighting.
Result
Depending on the data structure of the input, the result is either a sound power signal, a data series with sound power levels or a sound power level.
The Correction Terms
Correction term K0 for consideration of barometric pressure and temperature (see DIN 45635)
With K0 0 is not required, but for others it is (e.g., DIN 45635 precision grade 1). If you would like to use K0, select the option Use K0 and specify barometric pressure and temperature. Otherwise, remove the highlight.
Correction term K1 to account for background noise
Apart from the noise coming from the test object, there will always be background noise. The energetic sum of both noises are at the microphones. If the difference between the sum of noise coming from the test object and background noise (= noise measured at the microphones) to the background noise alone is smaller than 10 dB, a correction term must be specified. If the difference is smaller than 3 dB, the background noise is at least as loud as the noise coming from the test object, and the noise coming from the test object can no longer be determined.
You have several options for specifying the background noise:
•You can enter the measuring surface sound pressure level of the background noise directly in dB. To do this, select the Specify background noise option and specify the measuring surface sound pressure level of the background noise in dB. The measuring surface sound pressure level is the sound power level minus the measuring surface dimension Ls.
•You can obtain the background noise from a data set. To do this, select the Obtain background noise from level data set and choose a data set that represents the background noise. The data structure of this data set can be a level signal or a sound level scalar value (if, for instance, it was calculated by the Sound Level analysis object or a sound power level (if, for instance, it was calculated by the Sound Power analysis object).
Correction term K2 for environmental correction
Whenever measurements do not take place in a free field, reflections from the environment of the test object must be expected. Environmental correction can be calculated from room properties such as size, reverberation time or mean absorption coefficient of the room surface. You can obtain these details from the manufacturer of the measuring room.
There are several ways of specifying environmental correction:
•Select Fixed K2 if you want to specify the correction term K2 directly in dB and specify K2 .
•Select Mean absorption grade if you want to have the correction term K2 calculated via the geometry and the attenuation properties of the measuring room. Next, specify the Mean absorption grade (number between 0 and 1), as well as the Height of measuring room, the Width of measuring room and the Depth of measuring room. The calculated correction term K2 is displayed.
•Select Reverberation time if you want to have the correction term K2 calculated via the geometry and the reverberation time of the measuring room. Next, specify the Reverberation time in seconds as well as the Height of measuring room, the Width of measuring room and the Depth of measuring room. The calculated correction term K2 is displayed.
Before making the calculation, specify the correction term K2 of the measuring surface dimension Ls.
Correction term Ls (Measuring surface dimension) for the size of the measuring surface
The total acoustic energy that is emitted by the test object passes through the enveloping surface assumed around the test object, regardless of how large this surface is and how far the microphones are from the test object. The sound pressure recorded by the microphones decreases if the microphones are further away from the test object or if a larger measuring surface is selected. The size of the measuring surface is accounted for in the measuring surface dimension Ls.
There are several ways of specifying the correction term Ls:
•Select Fixed Ls if you know the measuring surface dimension Ls for your measuring surface. Specify Ls directly in dB.
•Select Fixed surface if you know the size of the surface. Specify the Surface in m².
•Select Sphere if you have a spherical measuring surface. Specify the Radius of the sphere in meters.
•Select Hemisphere if you have a hemispherical measuring surface above a reflecting plane. Specify the Radius of the hemisphere in meters.
•Select Quarter-sphere if you have a quarter-spherical measuring surface above a reflecting plane and a reflecting wall. Specify the Radius of the quarter-sphere in meters.
•Select Octant-sphere if you have an octant-spherical measuring surface above a reflecting plane and two reflecting walls. Specify the Radius of the octant-sphere in meters.
•Select Detached cuboid if you have a cuboid measuring surface above a reflecting plane. Specify Height, Width and Depth of the cuboid in meters.
•Select Cuboid at wall and ceiling if you have a cube-shaped measuring surface above a reflecting plane, on a reflecting wall and under a reflecting ceiling. Specify Height, Width and Depth of the cuboid in meters.
•Select Cuboid at wall if you have a cube-shaped measuring surface above a reflecting plane and on a reflecting wall. Specify Height, Width and Depth of the cuboid in meters.