50 . SECTIONAL ADDRESSES 



In the meantime the law is doing its best. A London magistrate was 

 recently courageous enough to describe that which is emitted from a 

 Scotsman's bagpipes as noise. A stipendiary ruled not long ago that a 

 violin and piano-accordion are ' noisy instruments,' and so is the human 

 voice, but only if used in a concerted piece with other instruments. A 

 firm of Galton-whistle manufacturers advertises ' silent dog-whistles ' 

 and so avoids any possibility of legal interference. 



There are two guiding principles when the question of noise abatement 

 is being considered. The one is that the degree of abatement of a noise 

 in a particular locality need be no more than will conform to the back- 

 ground of noise which obtains in that locality. The other is that in 

 a medley of noises, the loudest .must be tackled first to achieve any 

 appreciable benefit, after that the next loudest, and so on. This is illus- 

 trated by the fact that if there are two similar components and one is 

 ID decibels less intense than the other, the weaker one will contribute 

 only half a phon to the over-all loudness. 



I am reminded that to illustrate the somewhat meagre additive effect 

 of two equally intense sources, I was guilty a few years ago of perpetrating 

 an analogy based on crying twins. I now realise that the subsequent 

 march of events demands a more extended treatment, and so, for the 

 benefit of those who may be interested, I should add that ' quins ' 

 chattering simultaneously are 7 phons louder than one by herself, and 

 that the corresponding figure for ' quads ' is 6 phons, triplets 5 phons, 

 and twins 3 phons. 



The first line of attack on noise abatement, and in general much the 

 most eff^ective and economical, is to tackle an objectionable noise at the 

 source, and find the best means of reducing the output as much as possible. 

 The next step, possibly as a confession of failure, is to find a feasible 

 method of confining or ' smothering ' the noise in the place where it is 

 generated. In either case we turn to the engineer for help, and we may 

 anticipate that he is likely to be the more interested if he can see a potential 

 demand from the public. Fortunately the public is becoming sufficiently 

 noise-conscious to query the need for noises which it stigmatises as a 

 nuisance, so that there is now a goodly list of ' silent ' appliances in every- 

 day, life, though as regards many commercial machines and processes, it 

 is realised that the millennium is not yet and we must put up with second- 

 best expedients for the present. 



The path of a noise in its journey from source to hearer, may be either 

 via the intervening air, or via a sequence of solid materials or structures. 

 Experience has shown that the two effects require very different remedies 

 for abatement. The study of the general problem of noise transmission 

 is more complex than might be imagined, and some of the major diffi- 

 culties are not as yet completely resolved. For the practical elucidation 

 of the various factors involved, specially designed ' sound-proof ' 

 laboratories, such as those at the National Physical Laboratory, have 

 proved to be necessary. Parenthetically, it may be mentioned that the 

 N.P.L. acoustics laboratory, since its erection four years ago, has been 

 so fully engaged in transmission and absorption work, mainly for the 

 architectural profession and the building industry, that extensions are 



