DISPERSION OF SOUND 



281 



Table 12.1. absorption coefficients of various building materials and objects 



No. 



2 

 3 

 4 



5 



6 



7 



8 



9 



10 



11 



12 

 13 



14 



15 

 16 



17 

 18 



19 



20 



21 



Material 



Frequency 



128 256 512 1024 2048 4096 



Coefficient 



Author 



22' 



23 



24 



Draperies hung straight, in contact 

 with wall, cotton fabric, 10 oz. per 

 sq. yd 



The same, velour, 1 8 oz. per sq. yd 



The same as No. 2, hung 4" from wall . . 



Felt, all hair, 1", contact with wall .... 



Balsam wool 1" paper and cloth cov- 

 ering 



Rock wool, 1" 



Carpet, 0.4" on concrete 



Carpet, 0.4" on |" felt on concrete .... 



Cork board 1" 



Firtex i" on 2"x 4" wood studs 16" 

 O.C. 



Masonite §" board on 2"x 4" wood 

 studs 16" O.C 



Asbestos Felt 



Acoustex Excelsior Tile 1" 



Acousti-celotex type A jf" 441 small 

 holes per square foot 



Wood sheeting, 0.8", pine 



Brick wall, unpainted 



Brick wall, painted 



Concrete porous 2" block set in 1 : 3 

 cement, sand, mortar 



Plaster, lime on wood lath on wood 

 studs, rough finish 



Plaster, gypsum on wood lath on wood 

 studs, rough finish 



Ozite I" 



Individual Objects 



Audience, per person 



Auditorium chairs solid seat and back. 

 Auditorium chairs upholstered 



.03 

 .05 

 .06 

 .09 



.06 

 .35 

 .09 

 .11 



.22 



.16 

 .06 

 11 



.13 

 .10 

 .024 

 .012 



.15 



.027 



.016 

 .09 



.35 

 .36 

 .35 

 .39 



.46 



.37 

 .25 



.55 



.25 

 .18 



.23 

 .11 

 .070 



.025 



.51 

 .056 



.028 



.47 



P.S. 

 P.S. 

 P.S. 

 P.S. 



P.S. 

 V.K. 

 B.R. 

 B.R. 

 F.W. 



V.K. 



P.S. 

 W.S. 

 B.S. 



F.W. 

 W.S. 

 W.S. 

 W.S. 



B.R. 



P.S. 



P.S. 

 P.S. 



Absorption Units in Sq. Ft. (Sabins) 



W.S. 

 P.S. 

 F.W. 



Abbreviations in the above table are as follows: W.S., Wallace Sabine; P.S., P. E. Sabine; 

 F.W., F. R. Watson; V.K., V. O. Knudsen; B.R., Building Research Station, England; 

 B.S., U. S. Bureau of Standards. 



The average power of unamplified speech is much less than that required 

 for distinct hearing. A greater reverberation time increases the intensity 

 of sound at the auditor. However, increased reverberation decreases the 

 intelligibility of speech. These two factors oppose each other with the 



