ACOUSTIC IMPEDANCE. 37 



losses, and if the vibration amplitude were uniform over the whole 

 diaphragm, would be 789 V 0° acoustic absohms. The mass factor 

 of the diaphragm, as measured electrically, with its usual cover open- 

 ing into the air, was 0.263; so that if this mass factor had been 

 maintained under the geometrical conditions indicated in Figure 3, 

 the acoustic impedance on the outer surface of the diaphragm would 

 be 789 Y 0° X 0.263 = 208 Y 0° mechanic absohms. The actual 

 analysis, however, of the results with the tube attached as in Figure 3, 

 made the observed surge impedance on the front surface 187 'X 5?2 

 mechanic absohms. The discrepancy between the computed and 

 observed value of z^ may be attributed to three influences (1) acoustic 

 losses in the tube; (2) the sudden change in tube sectional area from 

 19.3 to 7.55 sq. cm. close to the diaphragm, and (3) a probable change 

 of mass factor mfM under the actual conditions of Figure 3. 



