A HIGH EFFICIENCY RECEIVER 



145 



The Electromagnet 

 As shown in Fig. 6, the electromagnet is of conventional design 

 except that the central pole piece has an opening through its center to 

 200 



zo 



Fig. 



2 4 & a 10 12 14 l<b 18 20 22 

 POWER INPUT (WATTS) 



5 — Variation of temperature of coil with direct current input. 



avoid a reaction of any air pockets on the diaphragm, 

 widely flared to prevent tube resonance. 



This opening is 



Experimental Results 

 It has already been pointed out that an ideal horn should have an 

 acoustic impedance at its throat equal to that of a tube of infinite 

 length and of the same cross-sectional area. In order to measure the 



Fig. 6 — Field magnet. 



10 



