^^ 



. .--^ 



y% 



^,,^-''' 



.-^ 



Fig. 8. When the wave length is larger than the mouth 

 of the horn, as in the low-frequency sound waves A^, 

 Ag, and Ag, there is little or no focusing. But with a 

 much smaller wave length a narrow beam of plane 

 waves is produced. 



71 



