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BELL SYSTEM TECHNICAL JOURNAL 



Since the characteristics of the horn are determined by the area of its 

 mouth and by its rate of taper the length of the horn is determined by 

 the area of the small end. This area is determined in turn by the 

 mechanical impedance and effective area of the system which it is ter- 

 minating, ^ls shown in Equation (22). It is seen, therefore, that the 

 length of the horn should not be considered as a fundamental constant. 

 A paper describing the design of horns based on these principles is being 

 prepared. 



An interesting feature of the horn which has been built commercially 

 is its method of folding. The sketch in Fig. 19 shows a shadow picture 



Fig. 19 — Sectional view of the folded horn showing the air passage 



of the horn. It will be noticed that the sound passage is folded only in 

 its thin direction, which permits the radius of the turns to be small and 

 thereby makes the folding compact. 



Fig. 20 shows the frequency characteristic of a phonograph designed 

 as shown above with a logarithmic horn w^hose rate of taper and area 

 of mouth opening place the low cut-off at about 115 cycles. It also 

 shows the characteristics of one of the best of the old style phono- 

 graphs. Curve A represents the new machine, while Curve B repre- 



