October 28, 1922] 



NA TL RE 



577 



at least 3 ft. by 5 ft. An adjustable organ pipe blown 

 at constant pressure formed the source of sound 

 placed at the focus of a 5 ft. parabolic reflector facing 

 the partition to be tested in the manner shown in 



Fig. 4, and a disc resonator was placed on either side 

 of the partition to measure the transmitted and re- 

 flected sound. Fig. 5 shows a photograph of the 

 apparatus in use, and the observer's box provided to 

 prevent disturbance due to his presence. The general 



and it was found that if the transmission through a 

 2-inch metal lath and plaster partition has an intensity 

 represented by 0-93, a 2-inch well-fitted solid wood 

 door with three-sixteenths of an inch clearance from 

 the floor increased this to 7-3 and with half an inch 

 1 learance to 11-7, showing the importance of even very 

 small apertures. As regards composite partitions, the 

 author's conclusions are that the small gain in internal 

 reflection at surfaces of different density is usually 

 more than counterbalanced by the loss in total rigidity; 

 and thus in reflecting power of the initial surface of 

 contact. In practice, of course, too much reflection 

 may be detrimental to the uses of the room in which 

 the sound is generated, and as is pointed out, absorption 

 must be the ultimate aim for the destruction of sound, 

 which means its conversion into heat. 



Sound-proofing is of special interest in the modem 

 type of business building, where, in order to economise 

 space and admit of adaptability for changes of tenancy, 

 the constructural brick wall has been so largely re- 

 placed by the thin partition, and experiments of the 

 type described should be of great value to architects 

 who are responsible for specifying materials and 

 construction. The present writer's experience is that' 

 a wall composed of Fletton bricks, which are very 

 dense, is less effective in stopping sound than one 

 composed of stock bricks, which are more porous and 

 less regular. 



It would be unwise to generalise too much from the 

 experiments described ; with floors, for example, the 



results of the tests confirm the views of earlier experi- 

 menters cited. Porosity results in absorption but a 

 good deal of transmission, while rigidity results in 

 large reflection ; the reflection from hair felt, for 

 example, being 6, while that from Sackett board of 

 the same thickness is 42-7. 



The effect of openings such as doors were also tested, 



NO. 2765, VOL. I 10] 



direct contact produces conditions different from those 

 of a sound wave in air, and through a solid concrete 

 floor every footfall may well be heard in the room 

 below. Much further work on this subject is needed, 

 and it is to be hoped that investigation in this country 

 will supplement and extend what is being done else- 

 where. 



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