Abstract
There are significant differences in the characteristics of machines and their noise radiation as well as in the purposes for which machine noise is measured. These have to be taken into account in developing practical sound test codes. If the data are merely to indicate whether the machine noise meets a specific criterion at a specific point of evaluation, measuring sound pressure at that point will suffice (see CAGI-PNEUROP sound Test Code). For general sound-control design purposes, however, sound-power spectra are necessary. Under both reverberant and semifree field conditions, great care is required when the noise contains pure tones [see ASHRAE Transactions 70 (1964) pp. 217 and 228]. The impedance seen by ducted fans has to be controlled as it will affect the sound power generated [see ASHRAE Transactions 74, Part 2, (1967), page V.1.1]. Machinery sound control by design also requires detailed knowledge of sound transmission paths. Transmission and insertion loss ratings and standards still do not cover many important configurations.
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