A.— MATHEMATICAL AND PHYSICAL SCIENCES 53 



one pretends, of course, that we can go back to the old methods, but if 

 we are to mitigate the noise nuisance in modern buildings, we must adopt 

 measures which are best incorporated during the designing stage. 



There is, too, another aspect which should be clearly appreciated and 

 that is if sound insulation in buildings is desired, it has to be paid for. 

 The public, at present enticed with a plethora of labour-saving devices 

 by landlords of flats, has yet to learn that reasonable acoustic privacy is 

 obtainable provided it is prepared to face a small proportionate increase 

 in the rent. 



(i) The insulation of walls and windows. — In the case of walls, par- 





3 



■« 





0/ 2 OS 10 2 SO 10 20 



Weight of partition ( Ibi per square foot) 



Dependence, of the sound reduction of single homogeneous 

 partitions upon their weight. {Sound reduction averaged 

 for freguencies 200,500,500, 700, 1000, 1600 s. 2000 cgcLes per second) 



Fig. 2. 



titions and windows, we have to provide defence primarily against 

 air-borne rather than structure-borne sounds. It is established that the 

 insulating value for air-borne sounds can be expressed in terms of the 

 extent to which an incident sound is reduced in intensity. A single 

 solid (or hollow-block) wall tends to behave like a piston which is lightly 

 held round the edges, so that the mean insulating value is governed by 

 weight alone, being roughly proportional to the logarithm of the super- 

 ficial weight, no matter what the material (see Fig. 2). High notes are 

 easier to stop than low, that is apart from vagaries caused by resonance 

 effects which occur at certain frequencies : these have been recently 

 explored by Constable. A window is usually the most vulnerable part 

 of a wall from the point of view of acoustical insulation. The weight 



