30 



ACOUSTICAL RADIATING SYSTEMS 



DIAMETER=-|X 



DIAMETER -3X 



90 90' 



Fig. 2.8. Directional characteristics of a circular piston source as a function of the diameter 

 and wavelength. The polar graph depicts the pressure, at a large fixed distance, as a func- 

 tion of the angle. The pressure for the angle 0° is arbitrarily chosen as unity. The direc- 

 tion corresponding to the angle 0° is the axis. The axis is the center line perpendicular to 

 the plane of the piston. The directional characteristics in three dimensions are surfaces of 

 revolution about the axis. 



1 5 15 15 15 15 ° 15 15 ° 15 15 g 15 



1000 ru 20000., 4000 <%> 7000 'o 10.000 <>. 



Fig. 2.9. The directional characteristics of a group of exponential horns, with a constant 

 flare and throat diameter of f inches as a function of the mouth diameter. The number at 

 the right of each polar diagram indicates the diameter of a circular piston which will yield 

 the same directional characteristic. The polar graph depicts the pressure, at a fixed dis- 

 tance, as a function of the angle. The pressure for the angle 0° is arbitrarily chosen as unity. 

 The direction corresponding to 0° is the axis of the horn. The directional characteristics 

 in three dimensions are surfaces of revolution about the horn axis. 



