Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/26/83; site ihuxm.UUCP 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