4 - Sound Power Level

Last edit: 15/05/2023


Given certain installation and operating conditions, the sound power level characterises the average flow of airborne acoustic energy emitted by the source into the environment. It characterises an intrinsic property of the source that is independent of the environment in which it is installed.

This value is often referred to as the “A” weighted sound power level, which is the most commonly used frequency weighting that gives results indicated as dB(A), very close to the response of the human ear.


Determination of the Sound Power Level

The sound power level can’t be measured directly with instruments. This value can only be calculated using those sound’s parameters that can be fisically measured.

These parameters are the sound pressure, the sound intensity and the vibrations caused from an acoustic source.

The standards mentioned in the EN ISO 3740 all use different roads to arrive at the same destination which is the determination of the sound power level: the standards ISO 9614-1 and -3 estimate the acoustic energly flow relying on sound intensity measurements, the standards ISO/TS 7849-1 and -2 take advantage of the vibrations produced by an acoustic source while the set of standards ISO 374X (except the ISO 3740) uses sound pressure values measured in specific positions around the test source.

Using these last stardards (ISO 374X) it has to be considered that the sound pressure level measurements will be influenced from the background noise and from the environment in which test are realized so the standards introduce the correcttion factors K1 and K2 to consider this aspect.


Accuracy Classes

For the set of basic international standards described in the EN ISO 3740, three different classes of accuracy grades define the quality of the determined sound power level value. These classes are:

  • Accuracy grade 1, called precision grade;
  • Accuracy grade 2, called engineering grade;
  • Accuracy grade 3, called survey grade.

For most uses, the application of methods providing engineering grade (grade 2) results is expected to be satisfactory.

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