SABINE. — ARCHITECTURAL ACOUSTICS. 



79 



below the point for Ci 64. Considering, however, the whole family of 

 curves and recognizing that each point is not without some error, the 



C3 c, c. 



Figure 12. 



C, 



The absorbing power of felt of different thicknesses. Each piece of felt was 

 1.1 cm. in tliickness. Curve 1 is for a single thickness, curve 2 for two thicknesses 

 placed one on top of the other, etc. As shown by these curves, the absorption 

 is in part by penetration into the pores of the felt, in part by a yielding of the 

 mass as a whole. Resonance in the latter process is clearly shown by a maximum 

 shifting to lower and lower pitch with increase in thickness of the felt. C3 (mid- 

 dle C) 256. 



curves as drawn are more nearly correct. The best method of reconcil- 

 ing the several curves to each other is to plot two diagrams, one in 

 which the variations in pitch are taken as abscissa and one in which 



