How to use absorption to reduce the noise in a room
Sound absorption is an important tool for designing good acoustic spaces because it helps reduce airborne sound. That’s the sound generated from conversations, radio, or that person eating lunch next to you, transmitted by air and atmosphere.
When we’re looking to achieve speech privacy in open offices, waiting rooms, or other sensitive areas of a building, consider distraction distance. When sounds are created in open spaces they will radiate out and distract people within a certain distance; consequently, an increase in distraction distance predicts an increase in disturbance by noise.
The Acoustical Society of America published an article in 2017 on the topic of distraction distance which proved the need to look at room acoustic design using absorption, blocking, and masking together to reach good working conditions in open-plan environments.
It’s also important to remember that when sound from the interior or exterior passes through a wall or roof assembly with ROCKWOOL stone wool insulation inside the cavity, you are already gaining a level of sound absorption. This is called cavity absorption. So when you think about it, you absorb noise just by insulating your interior walls to break the path of the sound.
What happens inside the room when sound is present—from either interior or exterior sources that hasn’t been controlled by the building envelope—is called room acoustics absorption. Here, either ceiling tiles or other materials with absorption properties are controlling the sound.
Overhead sound absorption demands can vary for the room, but the ROCKWOOL/Rockfon approach uses a “good, better, best” scale. Good = an NRC of 0.70, Better = an NRC of 0.80 and Best = NRC of 0.90 as outlined below, to create a good acoustic design, in particular for open environments.
This is because the ceiling is a critical element in open offices as well as meeting rooms, patient operating rooms, and classrooms. Adding to that, reaching the required sound absorption also shouldn’t limit your ability to develop a contemporary design. The NRC can be provided by any combination of baffles, islands, banners, acoustic metal decks, deck treatments. But based on our experience, ensure that you uniformly distribute the absorption across the space.
Why are ceilings so effective for sound absorption? Sound waves that rise above 5 ft. (roughly the space above chairs, desks, equipment and other surfaces that impact the path of noise) have to interact with the overhead surface before coming back down.
When the surface of that ceiling is absorptive, it is able to capture a significant portion of the energy. Stone wool acoustic ceiling tiles are especially effective at absorbing the reverberating sounds.
For more information about the factors and challenges presented by open-office-space designs, including what works and doesn’t work for occupants and how to address the acoustics, check out this podcast with Commercial Architect.
Physical barriers are another option for reducing noise in open spaces. This is not an argument in support of cubicles! Rather, consider using acoustic treatments on walls separating two spaces or interior zones.
This could include sound-damping panels (sound panels for walls that are installed after the room is finished to provide additional sound absorption) to reduce speech from traveling across the space. Or, when space is limited, using free-standing acoustic screens, furniture, or other sound-absorbing products that complement the room design might be a better choice.
Also, remember that to meet the criteria established for some high-performance settings, you’ll also need to consider how every structure, surface, fixture, material, and flanking path plays a role in the way noise is experienced. For the best results, this means thinking beyond walls for blocking sound and focusing on the true strength of ceiling panels—noise absorption.