HORN LOUD SPEAKER SYSTEMS 171 



F. Diaphragms and Voice Coils. — The diaphragm or cone of a horn loud 

 speaker in use today is made of aluminum alloys, molded bakelite with 

 various bases, molded styrol, fiber or paper. Typical diaphragm shapes 

 are shown in Figs. 8.1, 8.9, 8.10 and 8.17. Both round wire and edgewise 

 wound ribbon voice coils are used. See Sec. 7.17. 



G. Field Structures. — The field structures shown in Fig. 7.19 and 

 described in Sec. 7.18 are also used with horn loud speakers. In addition, 

 certain special structures are used as, for example. Fig. 8.9. In this case 

 the throat of the horn passes through the center pole. In general, it is 

 customary to use higher flux densities in the air gap of horn loud speakers. 

 Soft iron may be used for the pole tips of the air gap for air gap flux densi- 

 ties up to 20,000 gausses. For flux densities from 20,000 to 23,000 gausses 

 special iron (Permandur) ^^ may be used for the pole tips of the air gap to 

 obtain these high flux densities efficiently. 



H. Horn Walls. Vibration and Absorption. — In the theoretical analysis 

 carried out in this chapter it has been assumed that the horn walls are 

 rigid and nonabsorbing. In the case of certain materials such as wood, 

 paper and fiber the absorption of sound by walls of the horn may introduce 

 an attenuation of several decibels. The absorption may be reduced by the 

 application of lacquers and varnishes. The attenuation in metallic horns 

 due to dissipation is negligible. The vibration of the walls of the horn 

 distorts the response frequency characteristic and introduces " hangover " 

 and reverberation. The response to transients is usually poor when the 

 walls of the horn vibrate. This vibration may be reduced by increasing 

 the thickness of the walls and by suitable bracing. The vibrations and ring 

 in metallic horns may be reduced by coating the outside of the horn with 

 deadening material such as asphalt or pitch compounds. 



Elmen, G. W., Bell Syst. Tech. Jour., Vol. 15, No. 1, p. 113, 1936. 



