SABINE. — ARCHITECTURAL ACOUSTICS. 



81 



1.0 



.9 



.8 



.6 



2 3 4 



Figure 13. 



6 



The absorbing power of felt of different tiiicknesses. The data, Figure 12, is here 

 plotted in a slightly different manner, — horizontally on plotted increasing thickness, 

 — and the curves are for notes of different frequency at octave intervals in pitch. 

 Tims plotted the curves show the necessary thickness of felt for practically maxi- 

 mum efficiency in absorbing sound of different pitch. Tliese curves also show 

 that for the lowest three notes surface friction is negligible, at least in comparison 

 with the other factors. For the high notes one thickness of felt was too great for 

 the curves to be conclusive in regard to this point. C3 (middle C) 256. 



do not give any evidence in this respect in regard to the higher notes, 

 Cs 1024, Cs 2048, and C7 4096. 



It is of course evident that the above data do not by any means 



VOL. XLII. 



