Interiors Are Noisy Places But Buildings Can Be Retrofitted to Ensure Acoustic Comfort and Privacy

Left: The area of intelligibility around a speaker is not circular. Its shape is determined by numerous factors, including the orientation of the person speaking, as well as the physical barriers and absorptive/reflective materials used within the space.
Right: When sound masking is applied, the area of intelligibility shrinks.

Sound Solutions for Existing Buildings

Susan Orlandi, associate director and interiors practice leader at Skidmore, Owings & Merrill, San Francisco, points out there are a number of challenges when designing for acoustics in existing buildings, including high exposed ceilings, glass walls, hard surfaces and concrete floors that are in high demand in certain markets. Nevertheless, those challenges can be addressed effectively with proper strategies. “Typically, this involves reducing noise from building systems, such as HVAC and plumbing, improving sound isolation between spaces and collaborating on the interior design to achieve suitable room acoustics,” Orlandi explains.

Traditional solutions to help absorb unwanted sound include treatments on the floors, walls and ceilings. Carpet or cork flooring, fabric-wrapped panels, curtains, acoustic wall panels and acoustic ceiling tiles all help mitigate noise indoors to varying degrees of effectiveness. When comparing products, it’s important to consider their Noise Reduction Coefficient (NRC), STC (Sound Transmission Class) or IIC (Impact Isolation Class) ratings (see “Acoustic Ratings Glossary”). Additionally, Orlandi notes noise exposure modeling can assist in predicting future noise levels from a variety of sources to effectively address them. “The measurements and modeling are used to evaluate noise impacts and to develop mitigation measures to meet applicable standards and to minimize annoyance,” she says.

Although most facility executives are familiar with the elements needed to absorb and block noise, fewer know how sound masking functions, what’s involved with a successful implementation and how to tell if their system is doing its job, 32 to Moeller.

“Once a space is complete, if the walls’ real-world performance doesn’t live up to their lab-tested results, you can increase the masking level to make up for that deficiency—a flexibility uniquely afforded by this technology,” he says.

For example, an organization might have assumed it could rely on HVAC for a masking effect, only to discover upon move-in that this type of equipment doesn’t actually provide a reliable background sound level or produce a spectrum conducive to speech privacy. If masking was omitted from the original design, it’s also one of the most affordable and least disruptive remedies to retrofit in open and closed spaces. “Adding masking is far less costly and complex than upgrading the physical shell—and likely more effective,” Moeller notes.

Finally, technology has evolved to the point where acoustical engineers are beginning to study sound at the molecular level to address noise in the built environment based upon applied quantum physics research, Hsu says. “Using metamaterials and quantum physics applied to air molecules, quantum acoustics controls air at the molecular level,” he says. “As air is the medium on which sound travels, quantization removes the source of acoustical issues before they can exist by quantizing any air molecule before it contacts an interior surface.”

In other words, air is no longer a medium through which sound can travel because the technology forces sound to behave as individual particles rather than in groups or waves. Utilizing this groundbreaking technology, DHDI’s proprietary ZR Acoustics system is able to regulate all elements of sound, such as frequency response, amplitude, timbre, phase and resonance. It essentially renders walls, ceilings and hard reflective surfaces invisible— inaudible, rather.

Regardless of the products utilized to retrofit an existing space, it’s important to remember the most effective method of mitigating unwanted noise is a holistic one. Project teams that address acoustics early in the design process and leverage the expertise of consultants will be better positioned to build a sound barrier that works. And the sounds of silence will be music to the ears.

Acoustic Ratings Glossary

When comparing products to address acoustics, it’s important to understand their ratings in terms of effectively reducing, absorbing or isolating unwanted sound. Here are the most common classifications and what they mean, according to AcoustiGuard, a Mississauga, Ontario, Canada-based supplier of soundproofing products:

  • Noise Reduction Coefficient (NRC) determines how well something absorbs sound within a given space. It is measured using values between 0 and 1. An NRC rating of 0 indicates perfect reflection, meaning a material bounces 100 percent of the sound back into the room. An NRC rating of 1 indicates perfect absorption, meaning a material soaks up 100 percent of the sound.
  • STC (Sound Transmission Class) represents a material or product’s ability to block sound from traveling through a wall, ceiling, floor or other building assembly. It is the most common sound measurement system in North America, which is why it is associated with so many soundproofing products. The higher the STC rating, the better a material’s ability to block sound. STC is expressed as an integer and is calculated by taking the Transmission Loss (TL) values tested at 16 standard frequencies over the range of 125 Hz to 4000 Hz and plotted on a graph. The resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate TL Curve (or Transmission Loss Curve) to determine an STC rating.
  • IIC (Impact Isolation Class) measures a floor assembly’s ability to absorb impact sound, such as footsteps. It is represented by an integer or a whole number, where a larger number means more impact sound is being blocked. For example, bare concrete (150-millimeter thickness) has an IIC of 25; high-rated underlayment, like ISO-SEP 25HD, delivers an IIC of 62 for a single layer. Many building codes require a minimum IIC of 50.

Images: K.R. Moeller Associates LTD.

About the Author

Robert Nieminen
Robert Nieminen is a freelance writer; the former editor of Interiors & Sources magazine; and retrofit’s editor at large, specializing in interiors. Under his direction, Interiors & Sources was the recipient of several publishing awards, as well as a pioneer of sustainability reporting.

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