Building Noise & Sound Control:
This article series presents methods and materials used to control sound transmission in buildings: how to make a quiet home, office, or place of business using sound isolation for ceilings, floors, walls, plumbing, etc.
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This article series discusses noise and sound control in buildings, and includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. The page top illustration from the above text shows an example of a design to reduce transmission between building floors.
Because of its stiffness, wood framing (photo at left) readily transmits low-frequency sounds and impact noises through wood- frame houses. This is particularly a problem in floors and walls separating two housing units, but it can also be an issue within a single-family home.
For example, a person with a home office or music room might want to isolate it acoustically from the surrounding rooms so meetings or music proceed in private and so outside noises will not intrude.
Bedrooms located under living spaces can also require special treatment to reduce impact noises from above.
Another kind of noise control is important where a house sits by a highway or under a flight path.
The goal here is to keep outdoor noises from entering the house by reducing sound transmission through windows, doors, and exterior walls and ceilings. Special acoustical windows rated for low sound transmission are often required for substantial reductions in outside noise.
Sound can travel through both air (airborne sound) and solid materials (structure-borne sound). Structure-borne sound can be directly imparted to the building structure by a vibration, such as a humming compressor, or by direct impact, such as a boot stepping on a hardwood floor.
As sound energy travels through a building, it changes from one type of transmission to the other and back, losing energy in each transition. Because of its rigidity, wood framing is a very good transmitter of low-frequency sound and hollow wall cavities and thin doors do little to reduce sound transmission.
Sound levels are measured in decibels (dB), which are on a logarithmic scale. A sound increase of just 10 dB indicates an increase of ten times the intensity, although our subjective experience is that the sound is twice as loud.
Decibel levels for common sounds are shown in Table 5-14 at left.
Continuous exposure to sounds above about 85 dB can cause hearing loss in most people.
Sounds in an acoustically “live” room with all hard surfaces will seem loud and harsh due to the sound reverberating off the hard surfaces.
Adding sound-absorptive materials, such as carpeting and soft furniture, will make sound softer and more pleasant within the room, but will do little to reduce the transmission of sound to adjacent rooms.
To reduce transmission requires sound isolation strategies, typically using high- mass materials, double-framed walls, or resilient connections between the drywall and framing.
To keep airborne sound from passing through walls and floors, there are four main strategies:
A cavity with fiberglass is far more effective at blocking sound if the two wall surfaces (or ceiling and floor surfaces) are mechanically decoupled as in a double-stud or staggered-stud wall. Resilient channel works essentially the same way by breaking the vibration path from the stud or ceiling joist to the drywall.
The hardest sounds to block are low frequency, such as the thumping of a stereo bass. Using decoupled construction, such as double walls or resilient channels, is effective.
Where that is impractical, adding mass can also be effective. Very massive, non rigid materials such as lead or sand are ideal, but doubling or tripling the drywall is also helpful.
-- Adapted with permission from Best Practices Guide to Residential Construction.
Continue reading at ACOUSTICAL SEALANT CHOICES
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Technical Reviewers & References
As stated in Best Practices Guide to Residential Construction: Use fiberglass ductboard or fiberglass duct liners to quiet the noises of fans and moving air. Avoid sharing a common duct between two rooms that need sound privacy.
Elaborating on some duct insulation considerations: HVAC experts advise us that conventional practice is to insulate the interior of metal ductwork in order to minimize transmission of HVAC equipment sounds throughout a building. Some fiberglass duct liners are plastic coated and may be able to be cleaned using gentle procedures. But most common is the use of un-faced fiberglass duct interior insulation, typically treated with a surface resin binder to help reduce movement of fiberglass particles into the air stream.
Our fiberglass lined duct insulation photo (left) shows clean new metal ductwork with a pink fiberglass mat sound and temperature insulation installed on the duct interior.
However our work on indoor environmental and air quality topics suggests that from an indoor air quality maintenance view, we prefer to see insulation on the exterior of metal ducts. That approach permits the ducts to be cleaned, and it reduces the chances of mold growth in the ductwork. See DUCT SYSTEMS and see HIDDEN MOLD in OTHER PLACES for more about places to look for duct system defects and hidden mold on HVAC systems. Mold in Fiberglass Insulation illustrates problem mold growth in fiberglass inculation including in duct systems.
Construction of HVAC ducts from foil-faced insulating board combines sound and temperature insulation with aluminum foil to product ductwork that is quiet and cleanable.
As we show in our photo (left), white noise generators may also be used in locations where an extra measure of privacy is required. This installation is in the waiting room outside offices used by psychotherapists.
White noise is a sound containing a blend of all the audible frequencies distributed equally over the range of the frequency band. When this sound is generated it tends to make unintelligible or even less noticeable other sounds such as nearby conversation.
The proper setting for a white noise generator is not to make the output as loud as possible. Rather, set the volume on the white noise machine to just mask the noise (or conversation) to be overcome. Setting the white noise volume higher than that level risks making the white noise itself an annoyance in the building.
Shown is the Sleep Mate™ sound generator produced by Marpac. In addition to white noise, sound conditioners may produce sounds of nature such as that of a river or brook, lakeshore, surf, thunderstorms, or rainfall. Sound Screen® and SleepMate® are registered trademarks owned by Marpac Corporation.