302 



ARCHITECTURAL ACOUSTICS 



Equation 12.12 shows that the reduction is due to both the loss intro- 

 duced by the partition and the absorption in the receiving room. 



The choice of a partition for insulating a room against sound involves a 

 number of considerations. Some of the factors are the frequency distri- 

 bution and intensity level of the components of the objectionable sound, 

 the transmission frequency characteristics of the partition, the ambient 

 noise or sound level in the receiving room which will mask the objection- 

 able sound and the response frequency characteristics of the ear. 



Measurements have been made by various investigators upon the trans- 

 mission by single partitions. The results of these measurements arc shown 

 in Table 12.3. 



Table 12.3. noise reduction through various structures 



Material 



Author 



Aluminum, .025" 



Iron, .03" galvanized 



Lead, i" 



Plywood, i" 



Celotex, Standard {" 



Celotex, Standard §" 



Hair Felt, 1" 



Hair Felt, 4" 



Wood Studs, Wood Lath, Lime 



Plaster 



Tile, 2" Gypsum 



Tile, Clay 6"x 12"x 12" Plastered 



both sides 



Brick, 8" Plastered both sides 



Door, Light 4 Panel 



Door, Oak 



Door, Steel i" 



Window Glass, Plate j" 



Window Glass, Small Panes ys" ■ ■ ■ 



B.S. 



B.S. 



B.S. 



B.S. 



B.S. 



B.S. 

 P.E.S. 

 P.E.S. 



P.E.S. 

 P.E.S. 



B.S. 



B.S. 

 P.E.S. 

 P.E.S. 

 P.E.S. 



B.S. 

 P.E.S. 



The abbreviations in the above table are as follows: 

 P. E. Sabine. 



B.S. — Bureau of Standards; P.E.S. — 



The mass controlled partition with air between the partition elements 

 is a low pass filter in which the mass of the wall is the series element and 

 the volume between the partitions is the shunt element. See Sec. 4.10D. 

 The partitions in this case are mounted in edge supports which allow free- 

 dom of motion without cracks which would pass air borne sound. 



N. Nonlinear Distortion Generated in a Plane Sound Wave. — A sound 

 wave of large amplitude cannot be propagated in air without a change in 



