Foley Telephone Monthpiece 



199 



AN INVESTIGATION OF THE FOLEY TELEPHONE 

 MOUTHPIECE. 



James E. Brock, Sweetser, Indiana. 



One of the chief results of Dr. A. L. Foley's phctographic studies 

 of sound pulses through horns is the discovery that the condensing 

 power of flared horns is considerably less than what has been taught 

 by physicists heretofore.' The heretofore accepted theory is that the 

 condensing power of such horns is inversely proportional to the areas 

 of ci-oss-section of the ends." Researches by Foley, Cloud, and others 

 at Indiana University have shown conclusively that such is not always 

 the case. In fact, it was found that in flared horns there seems to be an 



Fig. 1. Foley telephone mouthpiece. 



actual "backing out" of some of the energy' which enters the wide mouth 

 of the horn, instead of all passing through, as the old theory demands. 

 It was also found that horns having a somewhat parabolic curvature as 

 indicated in figure 1 seemed to have much greater condensing powers 

 than those that are flared in the manner ordinarily found on telephone 

 transmitters. The net result of all these studies was the Foley Tele- 

 phone Mouthpiece shown in figure 1. As one would expect from the 

 geometry of the parabola a marked advantage of this type of horn 

 comes from the focusing effect of the curve. It was sensed that one 

 very serious fault of the flared horn mouthpiece was the fact that all 

 sound waves created in any instant did not arrive simultaneously at the 

 diaphragin of the transmitter, due to the fact that some of them had to 

 suifer reflections while others traveled directly in without impedence 

 of any kind. This was overcome in the case of the Foley Telephone 



' A Photographic Study of Sound Pulses Between Curved Walls and Sound Amplifica- 

 tion by Horns. Phy. Rev., Dec, 1922. 



"A. I.. Kimball, ColleRe Physics. Revised Edition, pp. 1!)(5-197. 

 ^ Ibid. See 1. 



"Proc. 38th Meeting, 1922 (1923).' 



