SOUNDPROOFING

 

Maybe your tenants are complaining that their drummer neighbor’s midnight band practices aren’t getting any better. Maybe you just want to watch your awesomely deafening, giant explosion-filled Michael Bay movies in peace. We have solutions for everyone.

SIMPLE SOUND BARRIER
We add extra drywall, Homasote, or popcorn ceiling material to preexisting drywall. This is pretty straightforward installation and provides some decent noise reduction – the kind you see (er, hear) in condominium construction. We recommend this for people who don’t mind being aware of their neighbors’ comings and goings.

SOUND INSULATION
A step up from the simple sound barrier, this is drywall/Homasote/popcorn plus insulation between the floor joists. We recommend this for people who want more aural privacy.

SOUND PROOFING
A step up from sound insulation, this involves all of the above, but more so. We recommend this for people who want still higher levels of quiet.

ANECHOIC CHAMBER
Thick walls and ceilings stuffed to the gills with insulation, interior of the room covered with baffling, acoustic damping tiles, foam, dead bodies, whatever it takes. Anechoic chambers not only let you hear the sound of your own ear canals, they also block outside radio frequency interference. We recommend this for musicians, loud movie watchers, and misanthropes.

 

You can take several actions to control noise. Although some must be handled during a major building or remodeling project, others are relatively easy fixes you can do anytime.


The Mechanics of Sound
The clapping of hands, footsteps on hardwood floors…all physical actions produce “sound waves” going through the air. When these “waves” reach our ears, they vibrate a sensitive membrane–the eardrum–and we hear them as sounds.

Noise is simply unwanted sound. In the home, most people consider noise to be just about any sounds other than those made by what they’re doing. For example, if you’re on the phone, you don’t want to hear the television in the next room. Conversely, if you’re watching television, you don’t want to hear phone conversations. And you probably don’t want to hear your teenagers’ music, period.

Unfortunately, most walls and ceilings are only marginally effective at blocking noise. They are built like drums. They have membranes–typically drywall–on both surfaces, fastened to solid structural members and separated by a cavity of air. Sound waves strike one surface carry through the structure and the air to the other surface, where they’re broadcast as audible noise.


What’s an STC?
Walls and ceilings are rated according to their sound-transfer performance. The key rating is called an “STC,” short for Sound Transmission Class. This rates the barrier’s ability to block or muffle voices and similar sounds; the higher the number, the more effectively the barrier buffers sound. A less-frequently used rating, the IIC (Impact Insulation Class), rates a wall or floor’s transference of impact noises, such as bumps and knocks (an IIC rating of 50 or higher is considered acceptable).

For residential partition walls, recommended STCs depend on the particular type of room: for bedrooms, an STC of 40 is considered good, 45-55 is very good and above 55 is excellent. Living rooms should be a couple of points higher; bathrooms and kitchens up to 5 points higher. Conventionally built partition walls have poor STC ratings of from about 15 to 35.

Building Quiet Walls & Ceilings
During building or remodeling, an effective and affordable way to improve the performance of walls and ceilings is to put batt or blanket insulation between studs or joists. Major insulation manufacturers, including CertainTeed, Johns Manville, Knauf Fiber Glass and Owens-Corning, market 3 1/2-inch-thick fiberglass or rock wool batts specifically for this purpose. Fiberglass or rock wool is excellent at absorbing the sound that would otherwise travel through the air spaces.

Designed to fit between studs, acoustic batts are 14 1/2″ or 22 1/2″ wide and 3 1/2″ thick–most are the same as R-11 or R-13 insulation batts. Kraft-faced batts are friendliest to handle and easiest to fasten in place (a vapor barrier is not needed for interior walls). They should be installed tightly between framing members, and snugly around pipes, electrical boxes, wires and heating ducts, with as few hollows or gaps as possible. Leaving only a small portion of a wall or ceiling uninsulated can dramatically reduce its sound-reducing performance. Batts can be friction-fit in wall cavities; if temporary support is needed, two or three bands of drywall tape may be stapled horizontally across studs. In ceilings, batts should be installed just above the backside of the ceiling material.

A conventional wood-stud wall packed with insulation yields an STC of about 38, better than the 15 to 35 STC of an uninsulated wall, but still considered low. Boosting performance to recommended levels calls for additional measures. Using metal studs helps; the same wall, built with 2 1/2″ metal studs, yields an STC of 45.

Another way to achieve better performance is to apply a second layer of 1/2″ gypsum wallboard to one side of the wall. This gives the surface more mass, making it less prone to vibrate and transfer sound waves. Adding this layer to one side of an insulated wall increases the STC to 40. Adding it to both sides will push the STC to 45.

An even more effective way to build an interior wall is to mount the 1/2″ gypsum wallboard on special, resilient channels that run horizontally across the wall. These channels absorb sound so it isn’t conducted through the wall studs, resulting in an STC rating of about 46. Typically, the drywall is screwed to a flange on these channels, not to the studs. Combining insulation, channel-mounted wallboard and a dual layer of 1/2″ gypsum on one side achieves an excellent STC rating of 52.

In roughly the same category is a wall with staggered wall studs. Though this requires more labor and framing material, a wall of 2 by 4 studs, staggered along 2 by 6 bottom and top plates with two thicknesses of fiberglass insulation produces an STC of about 50. Because the wall surfaces are each fastened to an independent set of studs, noise can’t travel through the studs from one surface to the other.

A floor-ceiling construction that produces an STC of 53 is to mount 1/2″ gypsum wallboard to resilient channels fastened to 2 by 10 ceiling joists, and install 3 1/2″ thick batts between the joists. In this scenario, the floor above has a plywood subfloor, particleboard underlayment, carpet pad and carpet.

Where codes and safety will allow, consider eliminating fireblocking in interior walls; these short blocks, mounted horizontally between wall studs, transmit noise readily from one wall surface to the other. If you’re thinking about doing this, be sure to check with your local building department.

Sealing Holes
Whether you’re building new walls or improving old ones, seal-up any place where air may leak through; where there is air, there is the potential for noise. Use flexible polyurethane or acrylic latex caulk or foam sealant to seal where pipes, wires, heating registers and any other objects penetrate the walls or ceiling. To avoid direct transfer of sound, switch and receptacle boxes and heating registers should not be placed back-to-back in a wall.

Sound-Blocking Doors
The biggest opening in a wall is the doorway. One of the most effective ways to minimize room-to-room noise is to install solid doors–and this is something you can do whether or not you’re remodeling or building. Standard hollow-core interior doors are poor sound blockers. According to Eric Ekstrom, Vice President of Operations at the National Wood Window and Door Association, “Any one of the particleboard core, composite core or solid wood doors would work much better at providing a sound barrier than a hollow core door. But most of the sound doesn’t come through the door, it comes around the door, so you would need to install weather-stripping to provide a seal.” Rubber bulb weather-stripping gaskets and a weather-stripped threshold should seal the gaps around the perimeter.

Of course, solid-core doors are more expensive, but you’ll find they’re available in a much broader selection of elegant styles. If you were to replace and weather-strip an interior door, what would be the result? According to Ekstrom, “If you did all of this, you could probably end up with a STC rating of 34 to 36.”

When planning for new doors and windows, also consider where sound travels. If possible, stagger doors along a hallway and arrange their swing so that they don’t deflect sound into adjoining rooms. Avoid sliding, bi-fold, and pocket doors where noise is a concern; they make noise and don’t seal as well as the swinging type.

Reducing Noise Makers
If you’ve ever stretched a string between two tin cans to create a primitive telephone, you know sound can travel along a physical object–a string–just as it travels through the air. With this in mind, opt for flexible furnace ducts rather than the rigid-metal type–or at least install flexible types between the air-handling equipment and the rigid ducts.

When possible, use resilient pads to separate pipes from framing members. Provide air chambers to eliminate water hammer caused when you quickly shut off a faucet. And caulk openings around pipes.

When purchasing new appliances, opt for the quiet ones. You’ll be amazed at the differences between conventional fans, dishwashers and the like and their newer, quiet counterparts. If possible, isolate noisy equipment, well away from sleeping areas. Dedicated equipment rooms with insulated walls and solid core doors are a good idea.

Choose Sound-Absorbing Surfaces
Hard surfaces reflect sound waves; soft materials absorb them.
Materials that help control sound within a room are familiar to most homeowners–if you want to minimize sound bouncing around within a room, opt for “soft” materials such as acoustic ceilings and padded carpet rather than hardwood, tile and laminates.

Companies such as Armstrong World Industries have a wide range of acoustic ceiling materials. Acoustic tiles and drop-ceiling systems offer excellent acoustic properties; people who think the conventional styles are a bit too institutional will like some of the newer varieties available. For example, Armstrong offers 2-foot by 2-foot panels that have a step-edged detail or look like embossed or molded plaster. “These are very good for blocking noise generated in the basement and keeping it from invading upstairs,” says Scott Qualls, marketing manager of Armstrong’s residential ceilings. “They will give your basement ceiling an STC of about 35, and even better performance if you install batt insulation between floor joist,” he adds. With ceilings as with the entire house, the most effective way to minimize noise is to combine several sound blocking and reduction methods.

To achieve a home that is not only functional but quiet takes a little work. But when you’re ready to put up your feet and enjoy a good book and you can’t hear the tube or the latest rock group, you’ll know it was well worth the effort. Silence is golden.

Acoustical Terms and explanations:

READ and UNDERSTAND these terms to tell us what you expect and to understand our proposal:

In alphabetical order:

A Weighing-A special electronic filter, built into most sound level meters that approximates the hearing characteristics of the human ear.

Absorption Coefficient-See Sound Absorption Coefficient.

ASTM-The American Society for Testing and Materials. An organization that standardizes acoustical test methods. ASTM also has test methods for other materials and purposes.

dB-See Decibel.

dB(A)-A unit of sound loudness, in decibels, measured with a sound level meter that has an A Weighing filter. The most common unit of sound loudness. See also Decibel and A Weighting.

Decibel-The most common unit of sound level (loudness) measurement. Zero decibels is the threshold of hearing, the quietest sound that most people can hear under ideal conditions.

:mrgreen: Diffusion-The scattering of sound. Usually in reference to the evenness of sound distribution in a room (no hot spot or dead spots). Also, a way to prevent echoes by scattering sound with surface irregularities rather than by absorbing it.

Echo-A discrete reflection of sound from a hard sound-reflecting surface resulting in an audible repetition of a sound. See also Reverberation.

Hertz-The unit of sound frequency: cycles per second.

😆 Masking-The covering up or obscuring of one sound with another sound. This is commonly done in open-plan offices where a random (pink) noise is played quietly through ceiling-mounted loudspeakers to mask or partially interfere with conversation from other workers. Masking is used to prevent distraction from neighboring conversation and to give an impression of privacy in the midst of an open-plan environment.

NC-See Noise Criteria.

😀 Noise Criteria-A standardized system of rating the ambient noise level (usually from HVAC) in a room. The NC value is roughly 10 points lower than the corresponding dB(A) level. A room with an NC-15 is very quiet such as a recording studio. An NC-35 is a typical quiet office level. See also Room Criteria. 95% of Acoustical Consultants use Noise Criteria.

Noise Reduction Coefficient-A single-number rating system (standardized by ASTM) used to classify the amount of sound absorbed by a material. The Noise Reduction Coefficient is the average of the individual sound absorption coefficients at 250, 500, 1000, and 2000 Hz rounded to the nearest 0.05. The NRC rating is most applicable to the absorption of speech sounds.

Noise-Unwanted, bothersome, or distracting sound. However, some noises can be useful: See Masking.

NRC-See Noise Reduction Coefficient.

Octave Band-A frequency band with an upper frequency limit equal to twice the lower limit. Octave band center frequencies used in architectural acoustics are at 125, 250, 500, 1000, 2000, and 4000 Hz.


Pink Noise-A type of random noise that sounds very much like the noise between stations of a radio or TV. Similar to white noise but with a different tone quality. See also Masking.

RC-See Room Criteria

Reverberation Time-The time it takes for a sound level to decrease by 60 dB after the sound is abruptly stopped. For most office and residential rooms the reverberation time is less than 0.5 second, in performance halls it is typically about 2 seconds, and in large cathedrals it can be 6 seconds or more.

Room Criteria-A standardized system of rating the ambient noise level (usually from HVAC) in a room. Both the Room Criteria and Noise Criteria systems have been in use during the past several years, but as of 1991, the Room Criteria system is the preferred method. For most purposes, the Room Criteria and Noise Criteria are equivalent. See also Noise Criteria. 95% of Acoustical Consultants use Noise Criteria.

RT,RT60-Abbreviations for Reverberation Time.

Sabin-A unit of sound absorption. One sabin is equal to one square foot of total (100%) sound absorption. The sabin was named for Wallace Clement Sabine (1868-1919), the “father” of architectural acoustics.

Sound Level-The loudness of sound, usually measured with a sound level meter. Sound levels are usually expressed in decibels (dB). See also Decibel.

😛 Sound Absorption Coefficient-The percentage of incident sound that is absorbed by a material. The remaining percentage of incident sound is reflected by the material. The NRC value is a number between 0 and 1.00. Multiply the number by 100 to get the percentage of sound absorption. A rating of NRC-0.00 indicates no (0%) sound absorption; NRC-0.50 indicates 50% absorption; NRC-1.00 indicates perfect (100%) absorption.

Sound Transmission Class-A single-number rating systems (standardized by ASTM) used to rate the sound insulation performance of a material or assembly. The Sound Transmission Class is most commonly used to rate the sound insulation provided by common building partitions. Typical office walls (gypsum board on studs) are in the range of STC-40 to STC-50. The STC number is roughly the number of decibels that a sound would be reduced when passing through a partition or assembly.

STC-See Sound Transmission Class.

T60-Another abbreviation for Reverberation Time.

White Noise-A type of random noise that sounds very much like the noise between stations of a radio or TV. Similar to pink noise but with a different tone quality. See also Pink Noise.