Acoustical Solutions: Sound Absorption and Sound Transmission

Acoustics play a crucial role in any environment, impacting everything from productivity in the workplace to the market value of residences. Though the science behind sound is well established, the act of implementing it to design a desirable acoustic environment is complex and a broad scope of solutions is used to address unique acoustical parameters. While all successful acoustic spaces start with strong structural and mechanical engineering, architects and designers create ideal acoustical atmospheres through materials, form, and spatial organization, turning the taming of noise into an expression of art as they tie together the needs of sound and structure. The information below reviews two acoustic categories that should be considered for improving sound in environments—sound absorption and sound transmission loss.

Acoustical Considerations

While there is no universal solution for resolving acoustical concerns, the particulars of the architectural environment in question play a crucial role—including whether or not it is a new build or existing structure. “The control of sound or noise (unwanted sound) in architectural spaces involves a number of acoustical considerations,” says Nereo Castelli, acoustic consultant at Acoufelt. “With a new build, the sound control is in the hands of the designer, so the selection of the type of barrier constructed rests on the assessment of how much noise is required to be controlled. The barriers are elements such as walls, ceiling, floors, and additional items such as doors and windows. In existing spaces many of these elements are already established and, depending on the building or space, these elements may be difficult or costly to upgrade. This brings into play the consideration of sound absorption versus sound transmission.” Although it is a complex science, it is beneficial to attain an understanding of two technical categories used in acoustics: sound absorption and sound transmission. “In all considerations, both new builds and existing, these two noise control tools should be used to reach the desired results,” adds Castelli.

Acoustical needs are often addressed across the categories of ceiling, wall, and flooring treatments, with materials that are designed to tackle both sound absorption and sound transmission concerns. “In flooring, we look at airborne sound and impact sound, with airborne sound referring to sound that bounces around an empty room; and impact sound which is the sound transmitted from a room above, through the ceiling, and into the room directly below,” says John Jarvis, technical services manager at Karndean Designflooring. Sound absorption products prevent noise from reverberating around a room, while high sound transmission loss materials serve to effectively stop sound waves from traveling into adjacent spaces. Materials used to block sound differ from those that are designed to absorb sound, and as such, they are subject to different rating systems for efficacy. Sound absorption products are given a Noise Reduction Coefficient (NRC) rating, while sound transmission materials are subject to a Sound Transmission Class (STC) rating.

Photography Courtesy of Acoufelt
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Sound Absorption

Referring to the elimination of reverberation within a space, sound absorption is the process by which sound waves are soaked up by surfaces. Sound absorption materials absorb unwanted noises within a room before they can bounce around the space, effectively lowering the level of background noises. “Sound absorption occurs when a sound wave strikes any surface and depending on the nature of that surface or body of material sound energy is converted to heat energy,” says Castelli. “Sound absorption is used within a space and can perform two functions: it can reduce reverberation within the space and thus reduce the noise within the space, and because of the reduced noise there is a corresponding reduction in the noise transmitted through the barrier into the other space.” Designed to dampen reverberation and reduce reflected sounds, effective sound absorption products include acoustic panels, tiles, and ceiling baffles, which are often constructed out of thick, porous, or fibrous materials.

Photography Courtesy of Acoufelt
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Sound Transmission

Sound transmission refers to sound that penetrates between adjoining spaces, making its way through dividing walls or floors. “Sound transmission (loss) is the prime barrier function in reducing sound from one space into another,” says Castelli. “The level of loss is dictated by the type of barrier constructed and there are many configurations depending on the application.” Preventing noise from leaving or entering a space, high sound transmission loss materials and products are typically installed inside walls, floors, or ceilings, and are not visible within a room. “When trying to isolate sound transmission, the building assembly is key,” says Jarvis. “There are many ways to diminish the sound transmission, including air space, insulation, ceiling tile, and sound underlayments that get installed under thick poured gypsum. You can often times pair an acoustic underlayment with your flooring to further reduce noise transfer.” Materials that perform well for high sound transmission loss are often heavy and impermeable, helping to act as a barrier in preventing noise from spreading from one space to another

Successful sound absorption materials reduce sound reflections and reverberations within a space, while high sound transmission loss materials provide noise insulation from one space to another. While both acoustical solutions mitigate unwanted sound, it is important to understand their differences.

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