Effective soundproofing — reducing sound intensity with respect to the source and your ears — involves a variety tactics. You can increase the distance between you and the noise source, add noise barriers to block or absorb the energy of the sound waves, use sound baffles and other damping devices to control noise within a room to quell the racket.
Soundproofing works through noise reduction and noise absorption. Noise reduction is achieved by distance and blockage. If you can’t move away from the source, you can place intervening objects, such as heavy walls, in the sound path. Noise absorption is achieved by changing the characteristic of the noise: suppressing echoes, reverberations, resonance and reflections and altering the frequency. This involves damping the noise that is within the room by using carpets, upholstered furniture, acoustical ceiling tile, interior walls and soundboard.
This cross section of a floor/ceiling sound-deadening system incorporates soundproofing plywood and drywall from Supress Products.
Construction materials make a huge difference in the transmission of sound. Sound Transmission Class (STC) is a rating for walls, doors, windows, etc. A higher number indicates less sound transmission. The walls in most homes are rated at about 45 STC or higher. Windows are typically less than 31 STC, and they are usually the primary transmission source of exterior noise.
The second biggest sources of noise leakage into the house are exterior doors, but correcting this problem can be more difficult. Unless you have an extreme noise problem, soundproofing the windows may be all that’s required.
Whether you’re building a new house or remodeling an existing home, wise use of construction materials is essential to soundproofing. Here’s how a variety of products work to reduce noise transmission:
- For exterior walls, concrete, brick and stone are excellent sound stoppers. For interior walls and ceilings, drywall is hard to beat. Mass equals effectiveness, if the material doesn’t weigh much, it won’t block much sound.
- Resilient channel is a half-hat-shape length of steel that is designed to stop the transfer of vibrations through the structure. Resilient channels work best on ceilings or walls to block large vibrations from sources such as overhead footsteps or loud speakers near an opposing wall.
- Mass-loaded vinyl (MLV) is a flexible vinyl barrier material designed to block sound transmission through walls and floors. During the manufacturing process, sand is added while the vinyl is in its liquid state so the material gains density.
- Lead-lined drywall is an excellent noise reducer, but it has two drawbacks: It costs $125 to $250 a sheet, and it can interfere with radio signals (from cell phones, wireless networks, etc.). Nonmetallic sound-suppressing drywall is a more practical choice.
- Acoustic ceiling tiles can be effective, especially when applied over drywall.
- Mineral-fiber sound insulation, which is installed in stud cavities and between floor joists, is much denser than fiberglass insulation and is specifically designed for acoustic usage. Sprayed-on foam-and-cellulose insulation that goes on wet is more effective than other types of insulation, but it is fairly expensive.
- Soundboard is designed to absorb noise, but it does not stop it. To be effective, soundboard must be installed on the outside of the drywall. An added layer of drywall may be a better and less expensive solution.
Some soundproof drywall products, such as Quiet Solution's QuietRock, use two material layers bonded with polymer to defeat noise.
Although the primary purpose of stud-cavity insulation is for energy conservation, some types can also reduce noise.
Materials that are not effective at reducing noise include loosely packed fiberglass insulation, dry cellulose insulation, rubber floor mats, foam rubber and standard forms of plywood and particleboard.
Soundproofing doesn’t necessarily require extensive remodeling; you can take a number of relatively simple steps to stop noise from leaking into your home. For starters, seal all holes in the outside walls, including entry points for utilities, with silicone caulk. Similarly, seal the trim around windows and doors. Although the space between the frames and jambs may be sealed with fiberglass or foam insulation, these materials may not block noise.
To reduce noise within your home, choose sound-absorbent materials such as carpets, large rugs, upholstered furniture, large pillows and heavy draperies. Fabric wall hangings and shelves full of books, plants and knick-knacks can also help to absorb noise. And when purchasing appliances (clothes washers, dryers, dishwashers, etc.) buy the quietest ones you can afford.
Even noise transmitted through HVAC systems can be reduced with the proper ducting.
Attacking weak links
Targeting the biggest noise leakers in your home — windows and doors — requires more effort. There are basically two ways to reduce sound flow through a window. The simplest and cheapest is to plug the window opening with 1-1/2 to 2-in.-thick closed-cell vinyl-nitrite foam wrapped with fabric. Most appropriate for bedrooms, this light-blocking solution can be used at night and removed during the day. (Vinyl nitrate foam is known by several trademark names such as America foam or Super Soundproofing Mat; you can find it on the Internet. For large windows, a backing board of 1/8-in. plywood may be necessary.)
The most practical option for living areas is to install a second window inside or outside of the window opening. (Double-hung windows are the hardest to retrofit.) This secondary window covers the whole opening, as does the original window. Frames are sealed to the structure using either compression seals, nonsetting mastics or flexible caulk. Opening panels are fitted with compression or brush seals to fill any gaps. Typically used for commercial applications, soundproof windows are usually manufacturer-installed.
Of course, you can buy a standard window and install it yourself. The secret is to prevent airflow through the window. Gaps or cracks representing just 1 percent of a window area can defeat the sound reduction by as much as 10 decibles Installing a second window should give you a sound reduction of 38 to 40 decibles. A minimum air gap of about 4 in. is recommended between windows. Higher levels of sound insulation are obtained as the gap increases to about 8 in. Above that, the improvement is minimal.
Doors also pose soundproofing problems for obvious reasons. Solid-wood doors offer the best noise reduction. Seal the edges and especially the bottom as if the outside temperature were 40 below zero with a howling wind.
Commercial storm doors help with energy conservation, but they provide negligible sound reduction. When a main entry door is a major source of noise, consider adding a second solid-wood door rather than a storm door. Ensure that both doors are sealed all around. If you can incorporate a vestibule or mudroom with properly soundproofed doors and walls, it can provide an excellent sound barrier.
Building up walls
An easy way to reduce sound transmission through an existing wall is to add a layer of 5/8-in.-thick drywall. First cut openings in the old drywall to increase the dead-air space (see illustration, below). Apply a thick bead of silicone caulk to the drywall opposite the studs. Staggering the drywall joints, attach the second layer using screws (which require fewer fasteners than if you use nails). Don’t allow the drywall to touch the floor; it will transfer sound into the floor.
When building a new wall between rooms, alternate the studs and split the 2x6 bottom and top plate to break the transmission of sound (see illustration). The same principle works on an outside wall with stucco, siding, brick, etc.
Insulate outside walls for energy conservation. Although fiberglass insulation is typically used, two other insulating products provide better sound control as well as a high R-value. Natural cotton fiber is relatively new and is available in R-30 batts. It is safe to handle (it doesn’t cause itching) and fire-resistant. Mineral or rock wool is an excellent sound and heat insulator, but installers must exercise caution when handling the product as it can irritate the eyes, skin and respiratory tract.
A ceiling with living quarters above probably needs as much attention to soundproofing as does an outside wall. Noises from conversation, foot traffic and entertainment devices easily transmit through the floor joists into the space below.
Installing sound-absorbent mat (acoustical mat) and resilient channel as shown in the illustration below works well. You can do much of the work yourself, though fastening drywall to the ceiling is never an easy DIY task; you may need to hire a drywall contractor for that task.
Sound-absorbent mat is made of lightweight closed-cell extruded polyethylene foam that is acoustically engineered to isolate sound vibrations and impact noises such as foot traffic from other rooms. The mat can be laid after the drywall has been installed in the upstairs room. It is laid directly on the subfloor and is turned up at each wall. A gypsum concrete or two-layer plywood raft floats on top of the mat and provides a rigid surface for the finished flooring.
The resilient metal channel used in this soundproofing method is designed to substantially improve the sound insulation of drywall walls and ceilings. It isolates the drywall from the framing studwork by reducing direct contact. The channels are about 1/2 in. thick with a wide flange that is mounted to the wall. They can be attached directly to studs or existing drywall.
The amount of time and money you’re willing to invest in soundproofing will depend on how much noise you can tolerate. If you do undertake major remodeling projects, be sure to check with your local code authority before you begin. Even if you choose simple methods such as sealing leaks and adding rugs and drapes, your efforts will enhance the peace inside your home — no matter what the neighbors are up to outside.
NOISE FROM OUTSIDE
Although you have little control over noise generated outside your house, sound barriers can offer some relief. Any solid mass (trees, earth, concrete) can help to block sound. For example, earthen berms and prefabricated barriers made of steel, concrete, masonry, wood, plastic, insulating wool or composites can minimize road noise. So the neighbor who mows his lawn at 6 a.m. may be a more significant nuisance than traffic from a nearby highway.
Active noise control (ANC) involves the use of devices to cancel out sound. A computer measures the offending sound frequency and amplitude and creates a new sound wave of the opposite polarity. ANC is relatively easy to effect in automobiles and airplanes, where the sound is repetitive, and in one-dimensional applications such as earphones. Creating this effect in a three-dimensional environment such as your bedroom, however, is far more complex and relatively expensive and requires professional expertise.