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ANNUAL REPORT SMITHSONIAN" INSTITUTION, 19 3 2 



foot of section rather than to its logarithm. Often a combination 

 of the porous flexible material and the rigid dense partition is 

 advantageous. 



It may here be mentioned that for the stages of talking-film studios 

 insulation values of from 50 to 70 decibels are aimed at according 

 to the circumstances. 



As regards multiple partitions, they should be wholly free of cross- 

 ties, that is, completely isolated from one another, if the combina- 

 tion is to be any better (as it may be) than one single partition of 

 the same over-all thickness. Whether or not a loose filling material 

 should be sandwiched between the panels is a matter for experiment, 

 as such a filler may or may not be beneficial. On the one hand, it 

 may act as an absorbent and a damper of vibration, and on the other 

 it may serve as a tie. 



Tablk 2. — Sound insulation values of rigid single partitions for air-home sounds 



1 4V2-inch brick wall. 



The question of protection from structure-borne noises is one to 

 which it is hoped attention may be paid in the new sound laboratories 

 which are to be erected at the National Physical Laboratory, as 

 there is need for systematic experiment. Heterogeneity and dis- 

 continuity appear to be of value, and loose fillers may prevent the 

 drumming of resonant panels or walls which is often an accom- 

 paniment to such vibrations and may result in pronounced sound 

 emission. 



In many houses the windows are the chief offenders in admitting 

 external noises. Sound-proof construction would be greatly simpli- 

 fied if windows could be abolished. This, of course, is not to be con- 

 templated, but we can at any rate use substantial windows of thick 

 glass. Opening a window even a little will, of course, largely nullify 

 the benefit of noise shielding and absorbing devices. Within limits 

 the amount of sound admitted by a crack or opening is proportional 

 to its area. In the case of a door or window affording, say, 30 

 decibels insulation, a crack with an area one one-thousandth of that 

 of the door would admit as much sound as passes through the door 

 or window. 



