THE ACTION OF CONICAL HORNS 



G. W. STEWART 



ABSTRACT 



Conical horns possess two aspects of considerable importance. In 

 the first place, they are an exceedingly important form of acoustical 

 apparatus. Again, there is no exact theory of the action of conical 

 horns and hence the only recourse for quantitative information is 

 that of experiment. 



Using two frequencies, i. e., 256 d. v. and 512 d. v., the following 

 experimental results were obtained with conical horns : 



1. If with a conical horn of fixed angle the length be altered with 

 the frequency of the received sound constant, it is found that the 

 intensity at the vertex of the horn passes through a series of max- 

 ima and minima with the peculiarities that the maxima are of the 

 same order of intensity and the minima increase with the length of 

 the horn, showing an amplification of the sound at all lengths greater 

 than that for fundamental resonance. 



2. There is an optimum angle for each of the frequencies, the 

 greater frequency requiring a larger angle at fundamental reso- 

 nance. For 256 d. v. the optimum ratio of radial length to diameter 

 is about 5 to 1. With 512 d. v. this optimum ratio is about 4 to 1. 



3. For a given frequency and varying lengths of conical horn 

 the optimum angle decreases as the frequency becomes an over- 

 tone of a higher order. The rapidity of this decrease when ex- 

 pressed in ratio of radial length to diameter of opening as a func- 

 tion of the order of overtone, is approximately the same for the 

 256 and 512 d. v. 



4. The variation of intensity with horn ratio is less marked the 

 higher the overtone. 



5. The resonance of any tube attached to a horn for listening 

 purposes will be superimposed upon the characteristics of the horn 

 itself but with resonance frequencies of the attachment modified in 



