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Path: utzoo!linus!decvax!tektronix!zehntel!ihnp4!ihuxm!gjphw
From: gjphw@ihuxm.UUCP
Newsgroups: net.misc
Subject: Re: sound insulation
Message-ID: <333@ihuxm.UUCP>
Date: Thu, 7-Jul-83 14:41:32 EDT
Article-I.D.: ihuxm.333
Posted: Thu Jul  7 14:41:32 1983
Date-Received: Sat, 9-Jul-83 13:10:43 EDT
Organization: BTL Naperville, Il.
Lines: 43


   A recent article asked for further information about ways to sound 
insulate the interior walls of a house.  This is a short tutorial about
sound insulation.

   Recently, I purchased a house which was built by the owner.  In an
attempt to add sound insulation, the owner insulated the interior walls
the same way the exterior walls were insulated: 3.5 inches of fiberglass
batt.  Predictably, this had little effect on the sound transmission
properties of the walls.  Thermal insulation is most efficiently realized
using materials that contain lots of air pockets (e.g., fiberglass, styrofoam).
Sound insulation can only be achieved by using construction techniques that
use no air (e.g., a good vacuum between the walls).  These two objectives are
somewhat at odds.

   Thermal insulation is intended to retard the heat flow between two regions
of different temperatures (e.g., inside and outside of a house).  The least
expensive technique to accomplish this involves installing materials that
prevent conduction and convention.  With their low specific heats and many
trapped air pockets, fiberglass batt and styrofoam are inexpensive choices.
About the most effective, and costly, means of thermally insulating two volumes
requires a vacuum (i.e., a thermos bottle or Dewar vessel).

   Since sound requires a medium for its travel, a vacuum provides the most
effective insulation against it.  Unfortunately, a vaccum is still quite 
expensive to produce or maintain under normal conditions (e.g., a household).
The second approach to sound insulation uses very heavy construction materials.
While the energy contained in sound is not lost, heavy materials absorb part
of this energy, reflect some, and retransmit some at lower frequencies.  These
lower frequency sound waves, often inaudible, are less objectionable than the
original.  Also, sound absorbing surfaces, which are designed to trap sounds,
can reduce the sounds that escape from the room in which they are generated
and thus reduce the background sound level in the entire house.

   So, in summary, if you want to keep in the heat, use fiberglass or
styrofoam.  If you want quiet, build with heavy walls, use sound absorbing
materials on the walls, and don't build the house near a highway.

                                                 Patrick Wyant
                                                 Bell Labs (Naperville, IL)
                                                 *!ihuxm!gjphw