VELOCITY MICROPHONES 



197 



seen that for R/\ less than .5 the phase of the pressure at the front of the 

 baffle leads that of the pressure in the wave. For values of R/\ less than 

 .1 the phase on the front leads by the same amount as the phase on the 

 back lags the pressure in the wave. 



o 



y-270 



O-360 



z 

 < 



< 



?-450 



•630 



'720 



3 4 5 6 789 



3 4 5 6 7 8 9 



Fig. 9.16. Computed phase frequency characteristic at the center, on the front and the back 

 of a circular baffle for normal incidence of the impinging sound wave. 



Equation 9.42 may be used to compute the difference in pressure between 

 the two sides of a relatively small ribbon located in a large baffle (Fig. 9.17). 

 The difference in pressure between the two sides of the ribbon in a circular 

 baffle, Fig. 9.17, is 



Ap = pg — pe+m 



9.45 



