Summation Methods in Noise Problems

Abstract

THE method of assessing the overall loudness of a complex noise by taking into account the frequencies and amplitudes of the component notes, and weighting and summing them, by calculation or instrumentally, has always been open to the suspicion that it may not apply to all types of noise. This suspicion has been confirmed as a result of noise measurements on electromagnetic apparatus such as transformers. Apparatus of this type constitutes a special case, as all the components have frequencies which are harmonically related. In contrast to this, the frequencies of the components of most other noises have no such special relation, being distributed irregularly over the audible range. This relation often exists, however, between a few components of other types of noise, such as that emitted by rotating machinery.