Acoustics In Creative Spaces
Programming RequirementsChallenging Conference Room – Room has two glass walls and an open ceiling. Open ceiling means no acoustical tile which is a huge opportunity to tame a space. Glass walls look great, but also create distraction on a video call. Currently the space is not used for video, but the right wall has been completely covered in absorption to remove direct reflections at ear height, and to counter the longer glass wall. Photo by Josh Rasch. Because of the costs involved to ensure proper acoustics, creative spaces are often used for multiple activities. Spaces may be scheduled to record a podcast followed by a practice session for a small ensemble of musicians. Later that same day, a job applicant may remotely interview for a position on a web conference, followed by a collaborative editing session of content captured out in the field by a team of videographers. Finally, that evening until the wee hours of the morning, a group of musician friends could unwind and play all their repertoire of tunes in a great space and capture all the highlights. Due to the multiple uses, the spaces may need to provide interfaces or controls for a range of user groups. Broadcast recording hardware and editing software may coexist with a touch panel programmed to launch a webinar or conference with a single touch (causing a series of actions to occur such as conference power and far-end connections, lighting scene, etc.). High-quality condenser and large diaphragm microphones used to capture the nuances of a fine string instrument might share space with a USB table mic plugged directly into a guest host’s computer used for a web conference. A truss or grid system with modular power and control connections for lighting subjects against a green screen backdrop may accompany a handful of permanent fixtures and a set control location. Regardless of the final version of the programming requirements, creative spaces often share many similar acoustical requirements. The spaces should be quiet or free from unwanted noise entering the room, and the acoustical “response” (what the room sounds like) must match the planned programs by carefully considering the size and shape of the space, along with the amount of absorptive and reflective surfaces. Background noise from mechanical and electrical systems must be minimized for success. Noise from these systems challenge the design team to abate sounds that travel both through the air and the building structure itself. Humans are excellent noisemakers by talking loudly right outside of a door or window of the creative space, playing music over loudspeakers, bouncing balls, dropping weights, dancing, etc. Exterior sounds like jet planes and rain noise must be addressed as well. Even in this modern age of sophisticated electronics with promises of noise-reducing processing algorithms, noise from diffusers that distribute conditioned air can easily be heard in many recording situations or during conferences that require voice communication. Many background noise types are “broad-band”, meaning that the noise is in the same range (or frequencies) as the “good stuff” one is attempting to capture. Signals that are highly processed in an attempt to eliminate the noise may end up substantially lowering the quality of sound being recorded or sent to someone listening on a call. Location of the acoustically sensitive creative space is paramount. Positioning the space away from loud mechanical equipment, bathrooms, kitchens or other noisy spaces avoids having to take expensive measures to block the sound later in the process. Sound transfer concerns must be considered from adjacent spaces that are both side to side, and above or below. If the room has an exterior wall or ceiling, the “weak link” of the structure such as windows or a poor performing roof deck can become flanking paths that lower the overall performance of the composite Sound Transmission Class (STC) rating, allowing more sound to enter.
Coordination during DesignOpen (left) to isolated (right) ceiling – Mechanical equipment is above the conference room. A spring isolated ceiling attenuates sound energy to create an environment suitable for the application. Photo by Josh Rasch. Because creative spaces are occupied spaces, they need to be served by typical building systems. However, there are key design practices that can be applied to ensure the acoustic needs are met. Both the architectural elements and building systems must be considered during design.
Architectural ElementsWindows are often used to allow natural light in and create excitement. Onlookers (when allowed), may be permitted to watch as a recording or high-profile interview is in progress. Often an acoustical window with laminated, double pane glass with dissimilar thicknesses and a large (insulated) frame are effective at providing the sound isolation required. Angled glass on the interior side provides both visual interest and acoustical benefits by eliminating flutter echoes between parallel surfaces or redirecting sound into an absorptive surface. Acoustical doors - especially pre-hung systems - or a sound and light lock (space permitting) provide excellent solutions for another room element vulnerable to sound transfer. It is critical to minimize penetrations and apply a non-hardening acoustical sealant when penetrations are required. A small hole or slit is all that is required to significantly reduce the performance of a partition wall. Partition walls should prevent enough unwanted noise from entering the creative space, but care should be exercised not to overdesign the walls as they are only as effective as the overall composite construction, which typically includes the lower-performing doors and windows. These will lower the composite sound transmission significantly if standard doors and windows are used. Acoustical products such as isolation clips that attach wall elements to studs or acoustical drywall with an integral “sound shock absorber” by including a layer of viscoelastic material allow designers to have thinner walls than in times past. One should consider an isolated ceiling or floor system to ramp up the STC and IIC (impact sound) ratings. More difficult situations for noise entering from above may require an isolated, sprung gypsum system, which does present design coordination challenges such as having to relocate mechanical equipment that must be accessed. IIC is considered less often than STC but is just as important. If the space above has a hard floor such as tile or laminate, impacts on the surface such as those from high heal shoes or sporting activities will transmit via structure and produce a great deal of noise. Introducing a sub-floor with a decoupling or “floating” layer into the assembly is a great way to combat this. Sound Diffuser – Designed to disperse sound and is typically used with sound absorbers to tune a space. Diffusers can break up standing waves and subdue flutter echo increasing clarity. Can also create a sense of spaciousness in critical listening environments like recording studios. Photo by Josh Rasch. A typical strategy is to install an acoustical tile ceiling or grid system with absorptive and diffusive materials to lower the amount of reverberation and direct sound to desired locations. Targeting the ceiling for absorption is ideal, as a large amount of surface area is usually available because the walls are often covered by other items such as technology and storage. The floor needs to have durability, and thin carpet tiles or other commercial carpets do not do a good job absorbing broad-band sound and completely ignore low-frequency energy. The grid can also be designed to support mounting lights and hide HVAC equipment.
Building SystemsInstalling acoustical lining in ductwork, preferably two inches or more will lower both the noise from the equipment upstream and prevent sounds such as voices from entering the ductwork and coming out in the next room. Elbows may be added to further reduce noise traveling down the ductwork, along with duct silencers if more drastic measures are required and the system can handle the additional pressure drop caused by the silencer. Adding liner will reduce the inside dimensions of the duct, resulting in a velocity increase of the air. This velocity increase will hurt acoustics, so the duct dimensions must be increased to maintain design velocity. For multiple acoustically sensitive spaces that are adjacent to one another, it is important to avoid running ductwork between rooms. Instead, it is better to run the main ducts down a corridor and bring branches into each space which extends the flanking path between diffusers. One should avoid locating variable air-volume (VAV) boxes or other distributed HVAC items in the space. Fully enclosing VAV or fan-terminal units later is very difficult and cost prohibitive, and factory attenuation packages provide only marginal improvements. Noisy lighting ballast drivers should also be re-located outside of the space. Providing isolation to structure-borne noise is often paramount. The chiller in the basement that has piping extending underneath the creative space will probably need to be hung with isolation hangers. The small mechanical pump room nearby will need an isolation base as well as hangers with resilient elements in-line for all the piping in close proximity. A digital room sign with touchscreen that shows the schedule for the space and ties into the network may be a required feature, allowing the room to be booked both locally and remotely with the proper credentials. The room sign may double for the traditional “on-air” light. Larger displays on the outside of the creative space may broadcast the event occurring inside, or a streaming encoder may be used to allow the event to be broadcast over the internet. If a public address system is required throughout the facility, a mute switch should be installed for the local speaker in the creative space with an emergency override circuit if required. The nature of the noise coming in, and the sound produced in the creative space going out is important to consider. If the other occupants in the facility are fine with hearing some of the activities that occur in the creative space, then the partition types should be defined by the noise or potential sounds entering the space, negating the need for more extreme and expensive measures. A voice entering the space would be much easier to attenuate than the subwoofers used to play back content inside the creative space that is radiating out. A video studio destined for interviews will not produce noise concerns to neighboring spaces but is concerned about noisy neighbors. Acoustical Isolation Products – Vibration Isolator (pink), and the rest are damping products for room isolation. Photo by Josh Rasch. Standard sound isolation ratings such as the STC for building elements do not account for the full-range of human hearing (125-5,000 Hz versus 20-20,000 Hz). The STC works quite well for speech frequencies as the tests includes the voice range, but a space for music recording may have a drum set with a kick drum requiring a higher STC wall assembly. Special attention with instruments that produce frequencies below 125 Hz (like a kick drum) should be paid to the wall assembly as the STC rating only covers down to 125 Hz. Two assemblies with the same STC rating can behave vastly different at 63 Hz which is often at the heart of the kick drum. As the demand for multi-use creative spaces continues to grow, the necessity for proper acoustics becomes all the more critical. Other than clear programming requirements of the space, there are a number of factors to consider both from an unwanted noise prevention standpoint and a sound isolation desire. During the design phase, it is important to consider architectural elements in play, active building systems and the nature of the application itself. Most importantly, acoustic engineers should have open communication with the client at the front end, so no stone is left unturned and the ultimate outcome meets the expectations. Josh Rasch is an Acoustical and Systems Engineer and David Bick is an Acoustical Engineer and Audio/Visual Designer at McClure Engineering, a mechanical and electrical consulting engineering firm dedicated to the development of innovative solutions to unique engineering problems.
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