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Aviation History
1931
1931 - 0423.PDF
FLIGHT, MAY 1, 1931 NOISE ki\ Thursday evening, April 16, before the RoyalAeronautical Society, Dr. A. H. Davis, D.Sc, of the Physics Department of the National PhysicalLaboratory, gave an exceptionally interesting lecture on noise. Noise, and its first cousin, vibration (orought one to say the elimination of them), should be paramount among the problems being tackled by anyonewho is designing commercial aircraft, for there is not the slightest doubt that it is the discomfort and annoyancefrom these causes in our existing commercial machines which prevent people using aircraft almost as freely asthey use any other form of transport. Here, then, was a lecture giving all the latest information and experiencegained by the sub-committee specially appointed to investi- gate this matter, and yet as far as one could see therewas not a single representative of any of our large air- craft manufacturing firms present. Practically the wholeof the audience were students, medical and scientific people, and with the exception of the Colonel The Masterof Sempill, Mr. Gordon England and Mr. M. L. Bramson, we saw nobody who was directly connected with thepractical side of aviation. It is not a little surprising that every firm in the country did not at least send oneof the senior members of their design staff, and we sincerely trust that this does not mean that they have notrealised the importance of the whole subject. Dr. Davis went to a great deal of trouble, for not onlydid he read his paper in an admirable and clear manner, but he also had no less than three assistants present,together with a large amount of apparatus, with the help of which he gave us some extraordinarily interestingdemonstrations bearing out his contentions and lucidly explaining exactly what noise was, and the methods which were being investigated to combat it. One of his firstexperiments was to give his hearers a demonstration show- ing exactly what was meant by a pure note of varyingfrequency from the lower limit of audibility through various stages, starting at about a frequency of 64 cyclesper second and finishing at about eight thousand. Then later, in explanation of the Decibel system of measuringsound, he demonstrated what the reduction of sound in successive steps of five decibels meant, and he showedthat notes of high pitch were still audible when their amplitude had been reduced to a figure where notes oflower pitch but of the same amplitude had become inaudible. As an explanation of his diagram showing thecontour of line of equal annoyance of pure tones, he said noisiness was a very difficult term to deal with, as notwo people could be in agreement on the subject. He then gave us notes of the same amplitude but of adifferent pitch, and it was generally agreed that those of the higher pitch, that is, from 1,000 to something over8,000 cycles per second, were those which caused most annoyance. At the end he demonstrated how complexsounds could be split up and measured by the Criitzmacher method. Mr. H. E. Wimperis (Director of Scientific Research)was in the Chair and introducing the lecturer, he said that we had to thank Dr. Davis for many things in con-nection with this subject, and amongst them was his great help in assisting us to understand and use theDecibel system in this country. The first part of Dr. Davis' paper dealt with thecharacteristics of sound, and must perforce be omitted here for want of space. Concerning noise in aircraft thelecturer said that the sheer loudness of noises in many COMFORT IN THE AIR: The cabin of the latest Short "Kents" sets a new high-water mark in comfort. The chairs are large and comfortable, and there is plenty of leg and elbow room, as well as head room. Noise has also been reduced very considerably, so that, altogether, passengers should be able to make the Mediterranean crossing without fatigue. 391
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