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From: eda@tekid.UUCP (Ed Averill)
Newsgroups: net.misc
Subject: Re: sound insulation
Message-ID: <1390@tekid.UUCP>
Date: Tue, 12-Jul-83 06:05:53 EDT
Article-I.D.: tekid.1390
Posted: Tue Jul 12 06:05:53 1983
Date-Received: Tue, 12-Jul-83 20:10:40 EDT
References: ihuxm.333
Lines: 43


        This is a real sore spot with me, so I'll pass a bit 
of info along. 

       There is a real inexpensive way of getting great 
reduction in sound conduction.  It is to use "offset studs".   
The standard sheetrock wall surfaces are placed on studs that 
do not connect through the wall.  This is most easily done in 
standard construction with six inch plates at the top and 
bottom, and with 4 inch studs placed alternately against each 
edge at intervals to support the size sheetrock in use.  The 
effectiveness comes from the low resonant frequency, and the 
low Q of a sheetrock resonator.  It should be a standard 
construction technique for seperating sleeping areas from the 
rest of the house, unless there is some other two-wall barrier 
like a closet.  I also used fiberglass batting on the premise 
that it would help disperse high frequency noise.  My success 
is so complete that sounds from my living room are perceived 
to come from the opposite direction in the adjacent bedroom 
because the hallway leads around to a door there.  While this 
is a standard technique in industrial construction, it took 
some heavy emphasis to get my home contractor to put it in.  

       The other sound path that is hard to control is 
ductwork.  I suspect that the answer there is massive baffles 
for low resonance, probably at the center of a star 
distribution system. This is the significant path for noise 
from one end of our house to the other.  I can understand my 3 
year old's requests for potty-help if my head is on the sofa 
next to the heating duct at the opposite end of the house.  
The duct has a straight shot through the central distribution 
point to there. 

        There are good references on this subject in libraries 
with architecture schools.  I have no memory of book titles I 
have read, but I remember clear discriptions of how to solve 
the ploblem.  The clearest analogy I ever ran into was that of 
transmission line theory. The energy must be dissapated 
somewhere, and will be reflected where there is significant 
impedance mismatch.  The logarithmic nature of the ear 
requires a lot of attenuation to be effective. 

Good Luck.