410 



BELL SYSTEM TECHNICAL JOURNAL 



20 





180 184 188 192 196 200 



FREQUENCY IN CYCLES PER SECOND 



Fig. 9 — Acoustic impedance of 112 foot open tube, 0.7 inch in diameter, coiled 

 into helix. Measuring frequencies chosen at half and one cycle intervals to show 

 oscillatory character of impedance. 



O 2 20 



1500 2000 2500 3000 

 FREQUENCY IN CYCLES PER SECOND 



Fig. 10 — -Acoustic radiation impedance of hole, 0.7 inch in diameter, in flange having 



diameter of 6 inches. 



the frequencies of interest. The dotted lines are the resistance and 

 reactance as calculated by the equations of Rayleigh.^ 

 9 "Theory of Sound," Vol. II, p. 164. 



