Sound Choices in Acoustical Drywall

New generation products deliver enhanced sound suppression solutions that reduce cost and offer revenue opportunities to developers.
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Drywall gypsum manufactured in the United States as opposed to Asia will reduce energy to ship overseas. Manufacturers with production plants across the United States can further reduce energy consumption associated with shipping its product across North America.  Shipping via rail is nearly four times more efficient that trucking.  According to statistics offered by Union Pacific, since roughly 200,000 pounds of acoustical drywall can be placed on one center beam railcar versus just 45,000 pounds on a truck. 

Thin Panel Construction.  Panels come in standard ½-inch, 5/8-inch, ¾-inch, and 1-inch thicknesses, with each successive width offering additional sound attenuation properties.  Some acoustically engineered drywall can achieve levels of soundproofing up to STC 78;  ¾-inch panels are recommended for home theater applications and 1-inch for professional recording studios, as these panels have the capability to reduce low frequency noise.    Depending on the wall construction, the 1-inch acoustical product can achieve STC 80+.

The Metal Factor.   There are different types of acoustical panels, some of which use metal and ceramic. Acoustical panels that use sheets of metal and cement or ceramic in layers in an effort to boost acoustical performance and fire resistance pose problems-they are difficult to cut and install correctly, and interfere with or prevent cellular calls, wireless network transmissions, and general communication with and between other wireless devices.

Effective in Remodeling.   Acoustical drywall can also be effective in renovation and remodeling situations.  The panels can be added directly to the existing standard drywall on one or both sides of the wall assembly and to the existing ceiling.  No demolition is needed, nor is there any need to remove paint from the walls, provided the walls are in reasonable condition. An existing room in a condo, an office or even a whole structure that is undergoing conversion from rental apartments to condominiums can be readily upgraded.  Other applications include existing hotel and motel rooms where excessive noise is a factor; a single layer of panel can be applied directly to walls and ceilings. 

Easy Installation. Because the acoustical drywall panels install and finish just like standard drywall, no special skills are required and installation can generally be handled by existing drywall crews, enabling builders to keep their labor costs in line.

The panels can also be easily cut with standard commercial drywall routers and saws.  It is important to measure the space and cut the panel to size, minimizing the gaps between panels and with other surfaces. Due to the aggressive nature of air- and structure borne sound, a contiguous application of the acoustical drywall should be made on all surfaces, meaning walls from floor to ceiling and with 100 percent coverage on ceilings, boxing-in recessed lighting, audio speaker fixtures, etc. with the same thickness of panel.  Every gap between the panels and any cut-outs or penetrations for electrical outlets, pipes, fire sprinkler nozzles and such should be sealed with special acoustical sealant.   After cutting, the panel is put in the correct position and attached with standard drywall screws measuring the appropriate length for the material and job.  The acoustical panels may be applied to either wood or steel framing or directly on top of existing walls.  Detailed installation instructions are often available on manufacturers' websites. 

 

How Sound Travels    

Sound can be classified into categories depending on its source:

  • Airborne sound travels through the air, as in conversation, traffic noise, or music. 
  • Structure borne sound is transmitted through walls in the form of vibrations.
  • Flanking sound, or sound leakage occurs through doors, windows, or other wall, floor and ceiling penetrations that create paths for sound.

 In a residential setting, sources of structure borne sound are washers and dryers, exhaust fans, and footsteps. Airborne sound becomes structure borne when it passes through floors, walls, and ceilings.  Structure borne sound becomes airborne when it is radiated by a wall.  Air- and structure borne sound are very aggressive in nature and tend to spread out through the entire building. Open attic areas and plenums above acoustical ceilings allow sound to travel.  Unless these paths are fully sealed-and that includes openings for recessed lighting, audio speakers, electrical outlets, fire sprinklers and the like-sound energy may pass through these areas, too, reducing overall acoustic performance.  To suppress any unwanted sound perceived as coming through a common wall, sound control coverage may have to be extended to the adjacent hard flooring surfaces, walls, ceilings or virtually any penetration in walls, ceilings or floors.

 

Traditional Methods

As an alternative to acoustical drywall, several traditional techniques can be used to control sound.  Alternatively, acoustical drywall can work in concert with traditional techniques such as using multiple layers of standard drywall, channels, sound boards, insulation and resilient clips.

Adding Multiple Layers of Drywall.   In simple terms, the thicker or heavier the structure, the harder it is for sound waves to penetrate it.  But other factors must be taken into consideration.  Adding layers of standard drywall to a wall will help to block the path of noise. Merely doubling a wall's mass, however, will not double its STC rating.  In fact, going to four layers of drywall on a typical stud wall yields only a small benefit, garnering only a 4-5 dB improvement. Changing a wall's sound attenuating capacity means making significant changes in mass.  Often, the sheer amount of mass that would yield meaningful benefits would be impractical from a cost perspective and would also reduce the usable square footage of a structure.  Simply adding multiple layers of drywall to a standard wall is considered by some to be the least effective way to improve sound proofing. 

Adding Absorptive Material. Adding insulation as absorptive material within the assembly will block some sound just as it blocks airflow.  The key benefits of insulation are best realized with mid- and high-frequency noise, such as conversation; however, insulation does lose its effectiveness against the low end of the frequency spectrum, such as that troublesome bass from the neighbor's stereo.  Insulation will have little or no effect on structural noise, so the HVAC system or a vibrating dishwasher or washer/dryer will continue to be audible.  Better sound control can be achieved via damping materials added to the assembly; these materials reduce the vibrations allowed to pass through to the adjacent room.  

Mechanical Decoupling.  Breaking sound's vibration paths by decoupling, or disconnecting two sides of a wall, will decrease vibration and increase transmission loss far better than merely adding successive layers of mass to a wall assembly.  Structurally decoupling the drywall panels from each other can result in considerable improvements in STC, though only in that part of the spectrum well above the low frequency resonance.

The same goal-reducing the sound movement from one side of the wall to the other through the studs-can be achieved to various degrees by different decoupling methods, including sound clips, resilient channels, double stud walls or staggering the joints between panels of drywall. Double stud walls offer the greatest potential to boost sound control and can achieve STC ratings of as high as 63 with improved low-frequency transmission loss, as well.  

 

 

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Originally published in May 2008

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