scope:

General

This standard gives engineering methods for determining in situ sound power using sound intensity measurements on a measurement surface enclosing a source. It provides guidelines on the acoustical envi ronment, including ambient noise, the measurement surface enclosing the source, and the number of measu rements on the surface.

This standard does not include specification of instruments or calibration procedures. It is not limited to anyone technique of intensity measurement.

Field of Application

This standard is intended for use primarily to determine the sound power radiated by sources in situ for the purpose of noise control, rating, and compliance with purchase specifications. There are no explicit restrictions on the size or shape of the source. The standard applies to any source emitting essentially steady noise during test, except those sources for which the measurement surface cannot be fixed in space. This, in most cases, should enable the sound power level of a noise source to be determined in its usual operating environment when the source of interest is a prominent source.

Measurement Uncertainty

Sound power determinations made in confonnity with this standard should result in standard deviations which are equal to or less than those given in Table 1. This table includes uncertainty in the sound intensity measurement technique due to the test en vironment. background noise levels, and selection of the number of measurement points.

NOTE: The standard deviations given in Table I reflect the cumulative effects of all causes of measurement uncenaint y. excluding variations in the sound power level from machine to machine or from test to test which may be caused. for example. by changes in the mounting or operating conditions of the source. The reproduc· ibility and repeatability of the test resu lts may be considerably beller (i.e., smaller standard devi ations) than the uncertai nties given in Table I would indicate.