A HIGH EFFICIENCY RECEIVER 



143 



showed that with this type of coupUng for a particular size of diaphragm 

 and throat area the cut-ofif frequency was raised from approximately 

 3,500 to 6,000 cycles per second. 



Fig. 3 — Diaphragm and air chamber. 



Principal Dimensions 



Effective mass of coil and diaphragm = 1.0 gm. 

 Effective area of diaphragm = 28 sq. cm. 

 Area of throat of horn = 2.45 sq. cm. 



force 



Stiffness constant = -——. — —. — ; = 6 X 10« dynes/cm. 



static displacement 

 Resistance of coil = 15 ohms. 

 Length of wire in coil = 760 cm. 

 Average flux density = 20,000 gauss. 



The diaphragm was made of a single piece of aluminum alloy 0.002 

 inch thick; metal was used in preference to other materials because 

 of its superior mechanical properties. The form and principal di- 

 mensions are shown in Fig. 3. A driving coil is attached directly to 

 the diaphragm near its outer edge. With this arrangement the di- 

 aphragm can be driven nearly as a plunger and it has little tendency to 

 oscillate about a diametral axis, as there is great rigidity against a 

 radial displacement of any part of the coil. The portion of the di- 

 aphragm lying between the coil and the clamping surfaces has tangen- 

 tial corrugations of the same type as described by Maxfield and 

 Harrison ^ in reference to a phonograph sound box. The inner portion 

 of the diaphragm was drawn into the form of two re-entrant segments 



^ Bell System Technical Journal, \'ol. \', pp. 493-523, July 1926. 



