DOUBLE SOURCE 



21 



wavelength and located close to the boundaries indicated above. For 

 example, A would correspond to a loud speaker, which acts as a simple 

 source, suspended in space at a large distance from any walls or boundaries. 

 B would correspond to a loud speaker placed on the floor in the center of 

 the room. C would correspond to a loud speaker placed on the floor along 



SOLfD- ANGLE PRESSURE 

 OF SOUND AT A 



EMISSION DISTANCE V 



PO'flZR ENERGY 



OUTPUT DENSITY 



DISTANCE r 



zrt 



2? 



41 



4p 



4W 



161 



8p 



641 



Fig. 2.1. The pressure, total power output and energy density delivered by a point source 

 operating in solid angles of 4ir, 2-ir, ir and Tr/2 steradians. 



a wall, and D would correspond to a loud speaker placed in the corner of 

 the room. Of course, as pointed out above, these examples hold only when 

 the dimensions of the radiator and the distance from the wall are small 

 compared to the wavelength. 



2.3. Double Source (Doublet Source )i>2'3.4. — a double source consists 

 of two point sources equal in strength ± A^-wA', but opposite in phase sepa- 



^ Lamb, " Dynamical Theory of Sound," p. 230, E. Arnold, London. 

 ^ Davis, " Modern Acoustics," p. 59, Macmillan Co., New York. 

 ^ Wood, " A Textbook of Sound," p. 64, Bell and Sons, London. 

 * Crandall, " Theory of Vibrating Systems and Sound," p. 135, D. Van Nostrand 

 Co., New York. 



