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BELL SYSTEM TECHNICAL JOURNAL 



resistance with frequency is largely due to the fact that the disturbances 

 generated at different points of the diaphragm do not reach the throat 

 of the horn in the same phase. To minimize this effect the air chamber 

 should be designed so as to make this phase difference as small as 



20,000 

 /xR (cgs UNITS) 



30,000 



Fig. 2 — Mechanical impedance of air chamber and ideal horn. 



possible. In the same figure, ^2 and .ro show the resistance and react- 

 ance respectively, if the diaphragm were moved as a plunger, i.e., with 

 the same amplitude and phase over its whole surface. It is seen that 

 the resistance is considerably larger and the cut-ofif frequency nearly 

 twice as high. These curves show the superiority of the plunger type 

 of diaphragm. 



In order to cover the desired frequency range the method of coupling 

 a diaphragm to the horn shown in Fig. 3 was adopted. Here the 

 disturbances reach the horn more nearly in phase without having to 

 pass through any restricted passages. The throat of the horn is flared 

 annularly to the point A. The disturbances reach the throat of the 

 horn from the inner and outer portions of the diaphragm approximately 

 in phase up to comparatively high frequencies. \\'ith this type of 

 construction it is possible to use a fairly large diaphragm so that large 

 amounts of power may be delivered without a great sacrifice in effi- 

 ciency at cither the high or the low frecjuencies. An experimental test 



