Soundproofing Done Right

Tips for keeping noise in or out of a soundproof room

By Vance Holloman

Photo by iStockphoto.com

While there are several ways to soundproof a room, doing it right requires a combination of several methods. Properly choosing and installing mechanical systems can lower noise levels passing through a room, but combining that with proper framing and sound-attenuation methods can result in a room that is completely soundproof.

Purpose

Usually the reason for soundproofing is to keep noise out or in. Sometimes it can be a combination of both. People seek to keep noise in a room such as a home theater or a room in which music is practiced or played loudly. Sound is usually kept out of offices or conference rooms, or even bedrooms in houses. Two-way soundproofing is usually desired in more professional settings, such as medical offices, where privacy while discussing delicate health concerns without interruption would be of a high priority.

Mechanical Systems

Heating and air conditioning supply and return ducts can transport sound from one part of a building into another. To prevent this unwanted sound transport, make sure that each supply or return is connected to a dedicated duct. Dedicated ducts run from the vent to the main HVAC unit without any other ducts being connected to them. This way, sound can't enter the duct from a vent in one room and travel to another room. Plumbing can be another source of noise penetration if the sink or shower/tub share a drain -- or, more importantly, a vent stack -- with plumbing fixtures elsewhere in the building. Design plumbing fixtures in the soundproof area to have their own drains and vent stacks.

Framing

Where space allows, frame a separate wall around the perimeter of the room, keeping the new wall an inch or two away from the existing walls. This will prevent sound from bridging the wall by passing through framing members. The dead space between the two walls will not allow much, if any, sound to pass through. If you are building the room from scratch, another option is to use a floor and top plate that is 2 inches wider than the wall studs and alternate the studs so that those on one side of the wall don't touch the other side of the wall. You are in effect creating two walls, but taking up less floor space by doing it this way. For either option -- or even if you choose not to add or stagger a wall -- apply a second layer of drywall over the first. Make sure that the second layer is of a different thickness than the first. An even better option is to cover the studs with lathe and plaster. While this isn't done much any more and it may be difficult to find someone to do it, it was the standard method for houses built before the mid-1960s. The density of the plaster will make it difficult for most sounds to pass through, even more so than two layers of drywall.

Sound Attenuation

Fill wall and ceiling cavities with insulation batts rated as "sound attenuating." These are available at most home improvement centers. Batts are typically 8-feet long and precut to fit between studs with either 16- or 24-inch spacing. For even better soundproofing, use mineral or rock wool in place of insulation or opt for specially designed foam-insulation panels purchased form a soundproofing company. Another option is to install sound-attenuating panels on the walls and even ceiling of the room. These are available from specialty companies that will take the size and finish materials of the room into consideration and recommend a certain size and number of the panels to be installed. They are typically foam panels covered with fabric that can be coordinated with the room's decor and are hung in much the same way as pictures or mirrors.

Room Accessories

While construction materials and insulation are used to prevent the passage of sound from one side of the wall to the other, room accessories that absorb sound can be used to limit the amount of sound waves that try and penetrate through the wall. Carpet and soft furniture do a better job of absorbing sound than hard furniture and flooring. Carpeting does a much better job of sound deadening than hardwood or tile floors, and carpet combined with an 8-pound pad does a better job than carpet alone or carpet with a lighter pad underneath. As an alternative, use special acoustical mats for the optimum in sound-dampening for the floor. Consider using wall hangings similar to blankets to help dampen sound before it passes through the wall. Floor-to-ceiling drapes, even along walls without windows, will also help deaden sound. In general, softer materials such as foam and cloth absorb sound more than harder surfaces such as wood, plastic, glass or leather. Select furniture that is stuffed and fabric-covered over wooden or leather-covered furniture with little stuffing or foam filling.