166 



HORN LOUD SPEAKERS 



efficiency characteristic is only a few per cent below the ultimate efficiency 

 characteristic obtained from the envelope of the family of characteristics 

 shown in Fig. 8.3. 



The two preceding horn loud speakers are suitable for high quality repro- 

 duction of speech and music. For certain types of announce installations 

 it is desirable to project intelligible speech over very great distances (one 



100 

 80 



z 



U40 



100 

 FREQUENCY 



1000 

 CYCLES PER 



SECOND 



Fig. 8.16. Efficiency characteristic of a diaphragm coupled to the horn of Fig. 5.8 and 

 driven by an aluminum voice coil of one-half the diaphragm mass in a field of 22,000 gausses. 

 yi. Without air chamber. B. With air chamber. 



to two miles) under all manner of conditions. This requires acoustic out- 

 puts of the order of from 500 to 1000 watts. The characteristics of 

 Fig. 8.14 show that it is not practical to build a horn loud speaker of this 



CROSS-SECTfONAL VIEW 



1000 

 FREQUENCY 



Fig. 8.17. Cross-sectional view and equivalent circuit of a loud speaker of two degrees of 

 freedom. The graph shows the efficiency frequency characteristic. 



capacity for the reproduction of the lower frequencies. A cross-sectional 

 view of a high power announce loud speaker and the simplified equivalent 

 circuit is shown in Fig. 8.17. The equivalent circuit shows a system of 



