Many people know of acoustical design as it relates to concert halls, where it is vital to maintain the quality of the sound throughout the hall or, when desired, embellish the sound. Even on a smaller scale, like in a classroom, acoustics are important. Architects must design these spaces so there is no echo and a student in the back can hear as well as one in the front. Although this type of design is important, it is not the only role of acoustics in architecture. If you’ve ever worked in an office where you can hear every work spoken in a private conference room or lived in an apartment where you wondered if your upstairs neighbor was bowling every night just before you went to bed, you are familiar with the other side of acoustical design.
Acoustical separation is one of the biggest challenges of architecture and interior design. This problem is exacerbated in mixed-use buildings where very different program elements can be happening within the same building. In a recent RODE project, the fit-out of a commercial space for a new spin studio, we were tasked with providing acoustical separation between the studio and its neighbors. These neighbors included a spa on one side and apartments above, both of whom would be sensitive to potential noise intrusion. Not ideal neighbors for a spin studio, especially one with loud music as a critical part of their brand and notes on their website that the “music will be bumping.”
Although there is a limit for any construction’s ability to block noise, it was our goal to do what we could to reduce it. Working with Acentech, our acoustical consultant, we developed a ‘box-in-a-box’ strategy
for the cycling studio. The two key elements of this strategy are mass and isolation. The isolation eliminates any pathway for the transference of sound and vibration, while the mass inhibits the transmission of sound from one area to another. A different method is used to achieve isolation and mass at the floor, the walls, and the ceiling:
At the floors, we employed a concrete floating floor system, the “Kinetics Noise Control RIM System”. This system consists of a 4” concrete slab on fiberglass isolators that prevent sound and vibration from transferring to the surrounding area through the base building floor slab. A resilient interface and acoustical caulking is used to keep the topping slab from contacting any base building elements along the perimeter. On our project this was the surrounding party walls, but in some cases, it will be the base building floor slab. Often the floating floor system is set in a depressed floor slab for accessibility, the RIM System is typically over 6” thick, requiring a ramp.
Built on top of the floating floor are the acoustical walls, which consist of a 2” gap from any other building elements, cold-formed structural metal studs, and four layers of 5/8” gypsum wallboard with acoustical insulation packed tightly in to the stud layer. The cold-formed metal stud can support the walls vertically but must be braced laterally. With typical wall construction this is done by extending the wall up to the underside of the structure above. This cannot be done here because it would transfer sound and vibration to the adjacent spaces. Therefore, the walls are braced against the surrounding party walls using resilient sway braces which eliminate any transference of sound and vibration.
The ceiling consists of a similar construction as the walls, with four layers of GWB on metal studs and acoustical insulation hung from above. Spring isolators are used at every hanger to keep sound or vibration from transferring. Hung from the GWB acoustical ceiling is an ACT ceiling to hide ductwork and allow for the installation of diffusers, sprinklers, and recessed light fixtures.
Because any weak areas in the system will allow for sound transmission, penetrations must be limited, and all joints and penetrations should be properly sealed using acoustical caulking. This is particularly critical because penetration can greatly reduce and, in some cases, eliminate the acoustical benefit of the construction. Another obvious weak point in the system is the door. There are many acoustical doors on the market but like anything else installing the right one is key. Acoustical doors, such as “Noise Barriers QuietSwing Door”, come fully assembled from the factory, which ensures the door properly seals in the noise. Kit-of-part doors are more susceptible to assembly errors which can, again, reduce or eliminate the acoustical benefit of the system.
As noted above this box-in-a-box system provides the mass (4 layers of GWB or 4” of concrete) and isolation (fiberglass isolators, sway braces, or spring isolators) to allow for our clients to create the music driven experience they desire while still being respectful of their neighbors. These similar strategies can be used throughout different projects.
Even if the system doesn’t need to be as robust the principles still apply. In an office where you need privacy between offices, or the shared walls of a multi-family residence, adding mass to the walls and sealing penetrations can create the needed privacy. Isolating mechanical equipment from the building structure avoids the transference of the noise and vibration to the rest of the building. Just as architects want the aesthetics of our projects to respond to their surroundings and we design the layout to work for the function of each space, acoustical design should be considered with the same specificity and care.