ACOUSTICAL DIFFICULTIES 
157 
away. It was therefore submitted to an accurate experimental 
investigation. The results are shown in the adjacent diagram, 
Fig. 15. Showing the relative efficiency of felt in differ¬ 
ent parts of a room having a barrel ceiling. Curve 1, 
normal absorbing power; Curve 2, absorbing power in 
the center of the room; Curve 3, absorbing power at 
the side of the room. C3 is middle C, 256. 
Fig. 15. In this diagram the curve marked 1 shows by its vertical 
ordinates the normal efficiency of a very highly absorbent felt. If