HORN LOUD SPEAKER SYSTEMS 



167 



two degrees of freedom. The compliance of the suspension system and the 

 comphance of the air chamber are chosen so that very high efficiency is 

 obtained over the range required for intelligible speech. A typical effi- 

 ciency characteristic of this type of loud speaker suitable for acoustic out- 

 puts of 500 to 1000 watts is shown in Fig. 8.17. Due to the large audio 

 power amplifier requirements, high loud speaker efficiency is an extremely 

 important economic factor. 



B. Multiple Horn Multiple Channel System. — The two channel or 

 " two way " system 2^'^^ is the most common example of a multichannel 



an 



HIGH FREQUtNCY UNIT 



LOW FREQUENCY UNIT 



A^ 



CROSS SECTION 

 LOW FREQUENCY UNIT 



L.F, 



ixp-^flfi; 



WIRING DIAGRAM 



Fig. 8.18. A two channel theatre loud speaker system consisting of a folded low frequency- 

 horn unit and a multicellular horn high frequency unit. The circuit diagram shows the 

 electrical filter used to allocate the power as a function of the frequency to the two units. 



system. This loud speaker, Fig. 8.18, consists of a low frequency folded 

 horn unit for reproduction from 40 to 300 cycles and a multicellular horn 

 unit for reproduction from 300 to 8000 cycles. 



In order to minimize time delay and phase distortion due to a large path 

 length difference between the low and high frequency horns, the effective 

 length of the low and high frequency horns must be practically the same. 

 It has been found impossible to satisfy this requirement in practical multi- 

 channel systems. The difference in path length in the system shown in 

 Fig. 8.18 is made relatively small by employing a short folded horn 

 coupled to a large diameter dynamic speaker mechanism. A further 

 reduction in path length between a short straight axis high frequency horn 

 may be obtained by shifting the high frequency unit backwards. 



The high frequency horn consists of a cluster of relatively small horns 



27 Wente and Thuras, Jour. A.I.E.E., Vol. 53, No. 1, p. 17, 1934. 

 28Hilliard, J. K., Tech. Bui. Acad. Res. Coun., March, 1936. 



