170 



HORN LOUD SPEAKERS 



multichannel system. However, from a technical standpoint the single 

 channel system is far superior to the multiple channel system. 



E. Folded Horns. — There are innumerable ways of folding or curling a 

 horn. Two different types of folded horns are shown in Figs. 8.18 and 8.19. 

 The principal purpose of folding or curling a horn is to use the volume 

 occupied by the horn more efficiently. Three more different types of 

 folding are shown in Fig. 8.21 . A simple folded horn is shown in Fig. ^.2\A. 

 A folded horn with a ring shaped mouth is shown in Fig. 8.215. The 



BOTTOM VIEW 

 A 



SECTION A-A 



B 



Fig. 8.21. Folded horns. 



SECTION A-A' 



c 



directional characteristics of a ring shaped mouth are sharper than those 

 of the rectangular or circular shapes having equivalent areas. See Sees. 2.6 

 and 2.7. The horn shown in Fig. 8.21 C is used for sending out radiation 

 over 360° normal to the axis. It is customary to mount this loud speaker 

 on a pole. 



The high frequency response is usually attenuated in a folded horn due 

 to destructive interference incurred by the different path lengths of the 

 sounds traversing the bends. In order to eliminate destructive interference 

 the same phase should exist over any plane normal to the axis. This con- 

 dition is practically satisfied providing the radial dimensions at any bend 

 are a fraction of the wavelength. Wide range reproduction of sound 

 requires a large mouth horn for efficient reproduction of low frequency 

 sounds and small dimensions at the bends of a folded horn for efficient 

 reproduction of high frequency sounds. Obviously, it is practically im- 

 possible to incorporate both of these features into a single folded horn. 

 It is true that folded horns have been used for years, but, in general, the 

 response at either or both the low or high frequency ranges has been 

 attenuated. 



