1.1 General--This SAE Standard describes a method for measuring the
weighted sound pressure levels at prescribed microphone positions in
the proximity of a device or machine for outdoor use, in order to
determine compliance with noise limits. The A-weighted sound power
level of the source is calculated from the measured values.
NOTE 1--When nine or more microphone positions are prescribed in the
proximity of the source (as in Section 7), the A-weighted sound power
levels determined in accordance with this document tend to result in
standard deviations less than approximately 2 dB, provided that the
spectrum does not contain pronounced discrete frequencies; if it does,
the magnitude of the uncertainties will be larger and no general rules
for the magnitude of the uncertainties can be given. These standard
deviations reflect the cumulative effects of all causes of measurement
uncertainty, 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.
NOTE 2--For measurements made using a hemispherical measurement
surface, the directivity index of the source may be calculated
according to the description of Appendix B.
NOTE 3--Measurement of A-weighted sound pressure levels at the
operator's position(s) is not described in this document.
NOTE 4--The results of noise measurements made according to this
document are obtained under prescribed conditions and will not
necessarily correspond to the noise experienced from the equipment when
it is in operation on a construction site.