RECORDIXC, AM) RUJ'KOnUCl \'C. 01' MUSIC JXl) Sl'LLCll 521 



The horn which has been used as a terminating resistance to the 

 mechanical filter structure is a logarithmic one. The general properties 

 of logarithmic horns have been understood for some time.^'' 



There are two fundamental constants of such a horn — the first is the 

 area of the large end and the second the rate of taper. The area of the 



Fig. 18 — Sectional drawing showing construction of the system shown in Fig. 17 



mouth determines the lowest frequency which is radiated satisfactorily. 

 The energy of the frequencies below this is largely reflected if it is per- 

 mitted to reach the mouth. 



From the equations given by Webster, ^^ it can be shown that all 

 logarithmic horns have a low frequency cut-ofT which is determined by 

 the rate of taper. If the rate of taper is so proportioned that its result- 

 ing cut-off prevents the lower frequencies from reaching the horn 

 mouth, the horn will then radiate all frequencies reaching its mouth 

 and very little reflection will result. ^^ It is, therefore, possible to build 

 a horn having no marked fimdamental resonance. 



" Webster, A. G., "Acoustical Impedance and Theory of Horns and Phonograph," 

 Proc. Nat. Acad, of Sci., 1919. 



'^ The authors wish to express their appreciation in this connection of the work of 

 Mr. P. B. Flanders who carried out the mathematical investigation of these relation- 

 ships and to Mr. A. L. Thuras who checked experimentally the mathematical theory. 



