The performance of noise meters in terms of the primary standard

The paper discusses the performance of noise meters, such as are used for engineering measurements, in terms of the primary standard of “Equivalent Loudness” which has recently been formulated. The unit of equivalent loudness is the British Standard Phon. The technique for the basic determination of the equivalent loudness of a noise is discussed, and the Phon values for a number of specific noises of importance in engineering are given. The fundamentally important equal-loudness relations for pure tones of differing frequency are considered, and the results of some direct determinations in the free field are given. The performance of subjective noise meters is then examined for noises of various types. A meter using two telephone receivers, which offers some advantage over the more usual types, is described. The performance of the objective type of meter is also examined. The measurement of noise associated with irregular sound fields is briefly discussed.