RESISTIVE AND REACTIVE LOAD 81 



k = 27r/X, 



X = wavelength, in centimeters, 

 CO = 2Trf, and 



/ = frequency, in cycles per second, 

 /i and Ki may be found in treatises ^"'^^ on Bessel functions. They 

 are also defined by the series, 



JiilkR) k^E? k'R^ k^R^ 



kR 2 22-3 22-3M ^ ^j 



The acoustic impedance of the air load upon one side of a vibrating pis- 

 ton in an infinite baffle is 



The impedance per unit area of the piston is 



The resistive and reactive components of the air load per unit area on one 

 side of a vibrating piston set in an infinite baffle is shown in Fig. 5.1. These 

 characteristics are useful in determining the radiation resistance and re- 

 active component of the air load on the cone in a direct radiator loud 

 speaker. It is also customary to use these characteristics for the imped- 

 ance at the mouth of a finite horn in computing the throat impedance. 



5.8. Resistive and Reactive Load Upon a Pulsating Sphere. — The pul- 

 sating sphere is a sphere whose radius increases and decreases with time. 

 The motion of the air around the sphere will, like the motion of the sphere 

 itself, take place only in radial directors and will have the same velocity in 

 all directions, but will depend upon the distance from the center of the 

 sphere. 



The mechanical impedance of a pulsating sphere is 



, ™ ( (kRY +jkR \ 



^"Watson, "Theory of Bessel Functions," Cambridge Press, London. 

 " Jahnke and Emde, " Tables of Function," Teubner, Berlin. 



