September 2017

The Science Behind Sound Damping

Pat Grotlisch and Frank Fuller

Designers and contractors have come under increasing pressure to reduce sound transmission between adjacent spaces in commercial and multi-family residential buildings. Driving demand for quiet are, among others, apartment dwellers who do not want to hear their neighbors’ music or the noise from the building’s community rooms; a business that wants a quiet workspace despite being next to the elevator shaft; and federal laws that mandate patient privacy in medical facilities. The solutions are the same whether the project is a condominium, an office building or a hospital.

Sound waves can pass through the materials used in buildings and through flanking paths. You can reduce sound transmission by acoustically decoupling partitions, sealing penetrations, adding mass and using sound-damping materials. It may require more than one approach.

Flanking Sound: What It Is And How To Reduce It

“Flanking” is the transmission of sound around building assemblies or through penetrations in the assembly. Flanking paths include the space above partition walls in office buildings, as well as penetrations in the floor and around electrical boxes. Failure to address these can derail an otherwise solid attenuation strategy. The best practices to reduce flanking sound include staggering electrical boxes, staggering board joints and using acoustical putty pads on electrical boxes.

Sound Transmission Class

Sound Transmission Class, or STC, measures how well a building material or assembly blocks airborne sound. The STC is a single number rating. STC is tested at one-third octave frequencies, from 125 to 4,000 Hz. This range includes normal conversation as well as everyday sounds. Sound-damping gypsum board (like 5/8” Gold Bond® BRAND SoundBreak® XP® Gypsum Board) is extremely effective at blocking this range of sound.

Sound Attenuation And Air Sealing

When sound hits the face of a wall, the wall will vibrate like a drumhead or speaker cone, transmitting sound waves from one side to the other. As mentioned above, sound can also move through airspaces or flanking paths, from one side of the wall to the other. Ways to attenuate sound include sealing the flanking paths, adding mass to the wall, decoupling the partition, using sound-damping gypsum board and adding insulation to the cavity wall.

Creating an airtight seal is an essential part of any sound-attenuation approach, regardless of the frequencies being targeted. It consists of sealing penetrations and gaps that create sound-flanking paths. These include gaps around electrical outlets, recessed lights, fire sprinkler heads, and doors or windows. Sealing is done with gasketing and acoustical sealant. Not sealing the perimeter of a wall can drastically lower its STC.

Reducing Stiffness

It is easier for sound to pass through a stiffer wall. For this reason, partitions with metal studs perform better than partitions with wood studs. In addition, partitions with framing 24 in. o.c. outperform those with framing 16 in. o.c., and partitions with lighter-gauge studs outperform partitions with heavier-gauge studs.

Careful Detailing Of Insulation

The secret with insulation is to not leave gaps that can create flanking paths. Research has found that leaving just 6 percent of the wall uninsulated will reduce the insulation’s sound attenuation effectiveness by 35 percent. When designing fire-rated partitions, it is important to follow the insulation guidelines of the rated assembly. Although it is common to use R-11 fiberglass batts in sound-rated assemblies, mineral wool or sound attenuation batts may offer better performance. Spray foam does a good job at sealing air gaps, but may not provide good acoustical performance.

National Gypsum Resources

When sound issues are a concern, which is increasingly common, National Gypsum has one of the country’s finest acoustical labs to test products. We also recommend that you review The SoundBook®, our acoustical assembly guide. Featuring 165 sound-rated assemblies, it is a valuable tool we created with you in mind.

Contact Your Construction Design Manager For More Information

Contact your construction design manager today for more information or if we can assist you in specifying the best gypsum board to help with your sound-damping requirements.

"Is it enough that National Gypsum Company already has a great product in SoundBreak® The answer is a resounding “NO.” National Gypsum is not inclined to stop at this. With more demand for sound-rated assemblies in more complicated designs, NGC is at the forefront of designing and testing new assemblies. An excellent example of this is the UL Design M514 (3/4” SoundBreak® XP® Floor-Ceiling Assembly). This assembly consists of 3/4” SoundBreak XP and resilient channel, fastened to 2x10 wood joists. This assembly is perfect as a floor-ceiling assembly, typically between units in multi-family projects. It provides 1-hr. fire resistance for the assembly, an STC rating of 58 (code minimum is 50) and an IIC rating of 57 (code minimum is 50). This is yet another example of National Gypsum Company’s commitment to providing the architectural community with solutions for its design considerations.”
- Frank Fuller

"When SoundBreak® is discussed, architects sometimes mention the higher cost of the board. But when discussing cost, we like to prompt architects to consider its value. Because when assessing its value, SoundBreak® is economical. Consider that to achieve STC results matching those of SoundBreak® would require multiple layers of Type X board, increasing installation costs and labor time. Using SoundBreak® also reduces the thickness of the wall and the footprint of the building — a major advantage where real estate prices are high. In addition, SoundBreak® installs and finishes like Type X board; it is not fraught with installation and finishing problems like other noise-reducing solutions. To further evaluate sound-reducing solutions, National Gypsum Company has published “The SoundBook®.” The SoundBook contains 165 assemblies that have been evaluated at NGC Testing Services, a nationally recognized, state-of-the-art acoustical testing lab. Applicable tests have been conducted in accordance with ASTM E90 and provide the STC test number and UL fire design number."
- Pat Grotlisch

Product Overview

Great For All Phases Of Finishing

Specify one of these hard-working ready mix joint compounds for an upcoming project:

ProForm® BRAND XP® with Dust-Tech® reduces airborne dust by 60 percent and allows quick and easy clean-up. Use it for taping, to finish joints and cornerbead, spot fasteners, skim and texture, and repair cracks in plaster walls. This formula provides a superior finish and resists mold growth per ASTM G21 with a score of 0 (best) and ASTM D3273 with a score of 10 (best).

Another excellent choice is ProForm® BRAND All Purpose. This formula applies easily and provides a strong bond and highly durable surface. Use it for taping, to finish joints and cornerbead, spot fasteners, skim and texture, and repair cracks in plaster walls.

Project Profile

Sustainable Single-Family House

Prescott Passivhaus
Studio 804
Norton & Schmidt

Designed to use minimal energy through affordable, passive means, this 1,700-square-foot house in the Prescott, Kansas, neighborhood, is just minutes from downtown Kansas City. To achieve its goal of a 90-percent reduction in heating and cooling costs, strategies including louvers, thermal mass, high-performance windows, super insulation, southern orientation and an airtight building envelope were employed. National Gypsum’s Gold Bond® BRAND eXP® Interior Extreme® Gypsum Panels are components of this project.

Read More About The Project

Continuing Education

Fall is a good time to wrap up some CEU requirements. Consider taking:

School is back in session. This month, we recommend taking:
1 hour/AIA HSW CE Hour
Understanding The UL Fire-Resistant Directory 101
1 hour/AIA HSW CE Hour

Protect Your Buildings With DEXcell®

Discover three great coverboard options with DEXcell® BRAND Roof Board.

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Amy Hockett
National Marketing Manager, Architectural Services & Sustainability

Trang Schwartz
Architectural Specialist

Scott Hughes
Northeast/Atlantic, Southeast/Gulf

Thad Goodman

Pat Grotlisch

Frank Fuller