Tufts — Transmission of Sound through Solid Walls. 449 



Art. XXXVII. — The Transmission of Sound through Solid 

 Walls ; by F. L. Tufts, Ph.D. 



Lsr a previous article* the author gave the results of some 

 experiments on the transmission of sound through materials 

 pervious to air. and it was shown that such materials behave in 

 the same way with respect to sound transmission and to the 

 flow of air currents through them. In the present paper 

 experiments are described which were undertaken for the pur- 

 pose of studying the transmission of sound through materials 

 impervious to air. 



On account of the increased noisiness of cities and the desira- 

 bility of excluding these noises from offices and dwellings, a 

 knowledge of the laws governing the transmission of sound 

 through various materials is becoming daily of greater import- 

 ance, and the present investigation was, in fact, suggested by 

 certain difficulties which had been encountered in excluding 

 noises from telephone booths. The experiments, described 

 below, were undertaken for the purpose of ascertaining the 

 essential qualities which a wall must possess in order to render 

 it impervious to the sound waves transmitted to it from the 

 air. 



Consider, for example, a sound wave traveling in air, and 

 suppose it to impinge upon a solid wall; there are three con- 

 ceivable ways in which the sound may be propagated through 

 the wall to the air on the other side : 



First, if the wall is pervious to air, the sound may be trans- 

 mitted through the air in the pores of the material. The laws 

 governing this kind of transmission were investigated in the 

 previous paper. 



Second, if the material is impervious to air, the sound may 

 be transmitted as an elastic wave in the material of the wall ; or, 



Third, the pressure of the sound wave against the wall may 

 produce a slight displacement of it, and the sound may thus 

 be transmitted as a vibration of the wall itself. 



The apparatus used in studying the transmission of sound 

 from the air on one side of an impervious wall, to the air on 

 the opposite side, is shown in cross section in Fig. 1. A and 

 B are two three-inch "gas unions," each fitted at one end 

 with a "bushing" which reduces the opening to one inch. 

 In these bushings, respectively, are screwed pieces of one inch 

 gas pipe, a and &, about one foot in length. Rubber tubes, c 

 and d, are passed through these pipes and are cemented in at 

 their ends with beeswax. The rubber tubes are connected to 



* This Journal, vol. xi, May, 1901, page 357. 



Am. Jour. Sci. — Fourth Series, Vol. XIII, No. 78. — June, 1902. 

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