Noise

Abstract

The nature of noise problems is outlined mainly from the mechanical engineering viewpoint, but it is pointed out that the effects of noise on normal people are generally small. The more important phenomena of the physical mechanism of sound are recapitulated and the explanation of hearing according to Helmholtz is given. Scales of measurement for both physical size and loudness are discussed, and it is shown how the enormous variations in magnitude of acoustical quantities led to the artifice of logarithmic measurement while it is emphasized that this “decibel” scale is not a subjective scale of loudness. From the research of Churcher, King, and Davies it is inferred that the idea of loudness is roughly proportional to the fourth root of sound power intensity. A brief account is given of the principal pieces of apparatus available for research, namely: stethoscopes, audiometers, both subjective and objective, frequency analysers, and silent rooms, and there is a section dealing with the interpretation of evidence thus obtained. The relations between various quantities are indicated in this section and a recommendation is made for the equipment desirable for researches into machine noise. It is suggested that attempts at elimination of a noise at the source are likely to be more profitable than acoustical treatment, in which latter category the phenomena of sound reflection, absorption, and confinement are noted. Problems are differentiated into those of air-borne and material-borne noise. There is also a note on the history of the subject, and appendixes are added containing: (1) some formulæ and tables of quantities; (2) a discussion on the units quoted in physical sound measurements, and (3) a bibliography. Since the reading of the paper, the recommendations of the British Standards Institution have dealt with the greater part of Appendix II.