HIGH FREQUENCY SOUND DISTRIBUTOR 



143 



clearances are required which introduce a loss. In addition, the space 

 factor in round wire introduces a loss. By using edgewise wound ribbon, 

 Fig. 7.18D, the space factor is improved and more conductor can be placed 

 in the air gap. 



7.18. Field Structures. — Five typical electromagnetic and permanent 

 magnet field structures are shown in Fig. 7.19. The most widely used 

 field structure for use with direct radiator loud speakers is depicted in 

 Fig. 1 .\9A. During the past few years materials for permanent magnets 



A-T 



SECTION A-A' 



E 



Fig. 7.19. Field structures. A and B electromagnetic type; C, D and E, permanent 



magnet type. 



have been improved and it is now possible to obtain high flux densities in 

 structures of reasonable size. These new alloys ^^ are combinations of 

 aluminum, nickel, cobalt and iron and have been termed " Alnico." Three 

 typical magnet structures employing these alloys are shown in Figs. 7.19C, 

 7.19D and 7.19E. For the design of field structures the reader is referred 

 to texts ^^ on magnetic circuit design. 



7.19. High Frequency Sound Distributor ^^. — The diameter of the 

 vibrating surface of multiple cones decreases with increase in frequency 

 and as a result the directional pattern is essentially independent of the 

 frequency. See Sec. 7.3 and 7.5. When a single uncorrugated cone is 

 used to cover the high frequency range the directional pattern becomes 

 quite narrow at the higher frequencies. By means of a distributor con- 

 sisting of vanes it is possible to spread the high frequency radiation and 

 thereby maintain uniform directional characteristics with respect to the 

 frequency. The high frequency contours of equal phase for a cone with 

 and without a distributor is shown in Figs. 1 .lOA and 7.205. The radius 



"Adams, J. Q., G. E. Review, Vol. 41, No. 12, p. 518, 1938. 

 i^Underhill, " Magnets," McGraw-Hill Book Co., New York. 

 16 Olson, H. F., U. S. Patent 2,102,212. 



