THROAT IMPEDANCE 



C-^ 5<4 ^^ f s 



Co h^ 



93 



where w = 2?!/, 



/ = frequency, in cycles per second, and 

 c = velocity of sound, in centimeters per second. 

 The radiation resistance of a mouth 10 inches in diameter is relatively 



e 



7 

 6 



5 



iff 



3 



X 

 O 



I' 



0.0 



2 

 -I 



-2 



-3 



-4 



-5*- 



100 



200 400 



FREQUENCY 



B 



-^ 



100 



200 400 



FREQUENCY 



'Ltci. 



1.25 

 ■1.00 



100 



200 400 



FREQUENCY 



1000 



a. .25 



"\^ l^^^^ I I I 



100 



200 400 



FREQUENCY 



Fig. 5.S. The throat impedance characteristics of a group of exponential horns, with a 

 flare cutoff of 100 cycles and a throat diameter of 1 inch, as a function of the mouth diam- 

 eter. S\ is the area of the throat in square centimeters. Note: the characteristic shown 

 is the throat acoustic impedance multiplied by S\ and divided by pc. r, resistive com- 

 ponent. X, reactive component. 



small below 500 cycles. The large change in impedance in passing from 

 the mouth to the free atmosphere introduces reflections at the mouth and 

 as a result wide variations in the impedance characteristic as shown in 



