Sound Control for Large Interior Spaces

by Mark Robins | September 1, 2021 12:00 am

Controlling noise may take several procedures and products to lower different noise sources to an acceptable level. Even for large interior spaces, there are noise reduction solutions and soundproofing options available. Understanding what they are and how to select them will create a successful acoustical design.

SOUND FACTS

To best learn how to contend with noise or at least keep it contained, first examine how sound waves work. When an object vibrates, it sets the air around it in motion. Sound pushes the air onward, and it’s heard when it reaches a listener’s eardrum and causes the eardrum to vibrate.

Metal reflects sound. “In interior locations this can be a major issue, from echoing the loud noise of a manufacturing process to the inability to hear a speaker in an auditorium or lecture hall,” says Nick Kaufmann, LEED AP BD&C, director of manufacturing and engineering, DuctSox[1], Dubuque, Iowa.

So, what are the factors that need to be taken into account to control sound waves when designing metal interiors and sound control/noise-proofing them? “Control of reverberation—how long sound takes to decay within a room—is key especially in large volume spaces, since the reverberation time increases both with volume and the amount of hard, sound-reflective surface area such as metal, concrete and glass,” says Jeremy Thorbahn, project director, Thornton Tomasetti[2], Halifax, Nova Scotia, Canada. “Noise buildup can quickly become excessive and speech intelligibility can be lost if some sound-absorbing material is not included in the design. Sound transmission both from other parts of the building or from the exterior environment must also be considered.”

Sound-absorbing materials absorb sound waves and make them disappear faster. When an object, like a wall, reflects sound, it causes an echo. This is because sound can bounce off of hard surfaces rather than sink into an absorbent material. Soundproofing materials prevent the transmission of sound by blocking sound. The sound transmission class (STC) is used to measure the ability of a material to block sound, whereas the noise reduction coefficient (NRC) measures the average of absorption at certain frequencies.

Alan Burt, partner at SSA Acoustics[3], Seattle, agrees that sufficient noise absorption in a large interior space is a key factor since metal acts as a reflective surface. “[This is true] whether utilizing perforated metal panels with sound-absorptive backing, or acoustical panels or clouds. Auditoriums and lecture halls need to be designed to focus the sound from the stage to the audience, which involves room shaping, and surfaces to reflect, absorb and diffuse sound. Industrial facilities often require a combination of localized noise control around equipment in addition to sound absorption to reduce the overall buildup of sound energy.”

Sean Browne, senior principal scientist at Armstrong Ceiling and Wall Solutions[4] in Lancaster, Pa., explains, “Fundamentally, the approach for acoustic design of a space is the same regardless of the type of space or the materials that are being utilized; the space needs to fit its purpose. If the space is for music performance, you will design to keep the ambient noise low and the reverberation moderate.

If the space is a conference room, where speech intelligibility with the space is important and speech privacy between spaces is crucial, you will design to keep reverberation low and sound isolation very high. If the space is a manufacturing facility, the ambient background sound level will need to be low to meet OSHA guidelines, so protection from machine noise will be crucial. The acoustic design needs to fit the use of the space.”

METAL AND NOISE

“When designing spaces that use metal ceilings and walls, considerations such as acoustical requirements are paramount,” explains Rick Loufek, director, Armstrong World Industries, Lancaster, Pa. “Our customers have told us acoustics is a primary consideration, which means we must address acoustical performance with every metal ceiling we produce.”

Metal is not typically a material that is thought of for its acoustical capability, but Thorbahn explains metal interior finishes are unique. “They are generally sound-reflective and contribute to longer reverberation. But, they can also provide sound absorption in the case of acoustic decks or perforated wall panels. Since metal roofs or floor structures are relatively lightweight compared to denser materials like concrete, they respond differently to sound transmission or vibration from equipment or human activity.”

“Metal is a relatively lightweight partition material, so it is not ideal for sound blocking and it is also not intrinsically porous, so it is not ideal for sound absorption,” Browne says. “However, it’s these qualities that make it very attractive as a component of sound-blocking and sound-absorption assemblies. Metal is very durable and cleanable and can be perforated with great precision. When backloaded with traditional porous sound absorptive materials (fiberglass, mineral fiber, etc.) it can become a very efficient sound absorber.”

Burt explains metal framing in wall assemblies is typically more resilient than wood framing. “[Because of this] the assemblies can provide more noise reduction than wood framing in a single stud wall assembly. Acoustical metal decking can often be utilized in spaces that require a lot of sound absorption such as gymnasiums or community centers. Steel is denser than wood or gypsum wallboard. Acoustical doors that need to meet higher STC ratings are typically steel construction.”

SOUND CONTROL DESIGN FOR LARGE INTERIORS

Browne explains that the thing about large interior spaces is that, “They sound like large interior spaces. Everyone knows what a gymnasium or an airport terminal sounds like just by looking at them. They have a lot of reverberation which can make speech intelligibility very difficult. Reverberation is the time it takes for sound to decay until it is inaudible. The longer the reverberation, the more sounds remain in a space and add to the background noise. Reverberation increases with the volume of a space but can be decreased with acoustical absorption. Large interior metal spaces will increase reverberation because the space is large and metal material on its own does not absorb sound. However, combining porous materials like mineral fiber or fiberglass to perforated or discrete arrays of metal elements can be a way of keeping the metal design and adding absorption to the space.”

“Designers should explore whether there is an acoustic version of a certain material that may be engineered to provide better sound absorption or sound transmission performance,” Thorbahn says. “If necessary, they should engage an acoustical consultant who can recommend appropriate design criteria for reverberation, sound transmission and vibration, and provide guidance on how to meet them.”

Burt agrees that working with an acoustical consultant is a big help in sound design and reiterates that the function of the space will define the criteria which will be used to guide the design of the space. “Generally speaking, if the space will have a lot of metal finishes, utilize perforated metal with sound absorptive backing. Design for acoustical response in a space includes a combination of materials that provide absorption, reflection and diffusion. A balance of these elements is most important in particular for design of performance or multifunction spaces commonly used for live music, lectures, dramatic performances, presentations, etc. There are metal building products that can be utilized for these applications.”

PRODUCTS FOR SOUND ISOLATION

Sound isolation attempts to keep sound contained in one space and not traveling into adjacent spaces. “There are a number of techniques used to increase the sound isolation capability of wall systems including multiple layers of drywall, decoupling adhesive, sound absorption within the stud cavity, etc.,” Browne says. “In addition, there are sound isolation clips, resilient channels, staggered studs and double-stud walls that will also de-couple adjacent spaces to increase sound isolation through walls.”

“For a big, reflective room, excessive reverb and echo are quite common, resulting in very poor clarity and intelligibility in the room,” says Chris Calzone, marketing manager and designer at GIK Acoustics[5], Atlanta. “The solution is to install absorptive panels, spread more or less evenly throughout the room. The number of panels—square footage of absorption—is far more important than where each one is mounted. Often, putting them on the ceiling or high on the walls makes the most sense—so they are out of the way—but there is a lot of flexibility to work around obstructions: doors, glass, video monitors, whiteboards, etc. You would want to focus your treatment on a range of square footage of coverage to be around 15 to 20%.”

Demountable and movable wall systems are growing in usage. These systems offer flexibility with space layout and configurations while reducing initial construction schedules, Browne says. “Acoustically, these systems will lack the sound isolation capabilities of traditional wall systems, but there are ways to enhance the absorption within a space and blocking between spaces by utilizing porous absorption in the form of attached treatments.”

Acoustic roof decks—typically perforated with insulation inside of the deck flutes—are commonly used in spaces like gymnasiums, schools and libraries for sound control. Thorbahn says there are also many acoustic metal wall or ceiling panels on the market that operate on the same principle. “Spray-applied acoustic coatings like K-13 [from Houston-based International Cellulose Corp.] are also highly effective for sound absorption and work well on bare metal surfaces. Resilient channels or isolation clips can be used to fasten ceiling or wall materials to a metal structure with a decoupled connection where increased sound transmission performance is required.”

Burt says perforated metal ceilings with acoustical backer can have a non-metal finish such as wood. “Curved metal panels can be used as ceiling reflectors for performance spaces.” Browne stresses that reducing sound transmission through ceiling systems is very necessary because the majority of wall systems are not sealed, finished and extended from slab below to deck above. “All demountable wall systems are like this by design; therefore, sound blocking ceiling systems must be used to reduce sound transmission through the ceiling plane,” he adds.

Unlike metal, fabric does not reflect sound, it absorbs it. Kaufman says when using his company’s DuctSox fabric overhead air dispersion product line, sound that hits the fabric does not reflect back. “Secondly, air diffusion sound can also be detectable in auditorium type of applications. DuctSox gives the combination of linear vent and the ability to perform under low static pressures, which result in quiet air distribution.”

GIK Acoustics’ Art Panels allows images to be printed onto the panels’ fabric of the panels, turning it into what Calzone calls, “a piece of sound-absorbing artwork. While performance is the same as a normal fabric panel, Art Panels open up a much wider array of aesthetic possibilities. Images can be chosen from our online library, or you can upload any image or logo for us to use.”

Source URL: https://www.metalarchitecture.com/articles/sound-control-for-large-interior-spaces/

---