By Benjamin Markham, LEED AP and Ioana Pieleanu
The days of an empty, sterile atrium with nothing but a security desk and a skylight are over. The atrium today is the heart of the building — the living room, dining room, lecture hall, performance space, and cocktail lounge all in one (while still serving essential circulation and security functions).
Atriums lend themselves to monumentality, and tend to feature glass and stone. At worst, these spaces can be cacophonous — we’ve all had the experience of trying to have a conversation over dinner, during a cocktail party, or at the reception desk and feel that we must shout to be heard. But it is possible to weave intelligent acoustical design seamlessly into the design of such spaces, maintaining both monumentality and liveliness while simultaneously fostering easy conversation and control over the build-up of activity noise.
A great example of such a space, with its many functions and resulting acoustical challenges, is the “Forum” in TripAdvisor’s new global headquarters in Needham, MA, designed by Baker Design Group. Providing space for 1,500 employees, the Forum (seen below) is a four-story atrium that serves as an enormous lounge, informal work or meeting space, dining room for breakfast and lunch functions, and auditorium for company presentations, lectures, and even music events.
When it comes to the acoustics for such a space, success falls within a rather narrow “sweet spot” defined by what is reasonably achievable in such a large and open volume, what is necessary for the most sensitive activities, and what is feasible within the constraints of the budget. Achieving just the right outcome requires very close collaboration within the design team (generally comprising the acoustician, AV consultant, architect, mechanical engineer, and the client’s representatives), and capable and effective engineering.
A few guidelines when establishing the acoustical goals for a highly functional atrium or commons…
One priority is to define a suitable background noise goal. A space that is quiet like a concert hall is neither necessary nor desired: the space will be uncomfortable due to a lack of speech privacy when only sparsely occupied, and the project will incur unnecessary and possibly exorbitant costs. On the other hand, a space that is too loud is not desired either, and for several reasons: noisy spaces are caught in a vicious cycle with occupants raising their voices to overcome the background noise, leading to yet more noise; understanding speech can be difficult (or at the least, fatiguing); and in some cases, such as recording, the space may be plainly unusable.
The right noise goal will follow from the space’s uses. For example, if there is a significant performance component, the background noise goal could be on the order of 10 decibels more stringent than otherwise.
The next step is to define suitable sound isolation goals to and from adjacent interior and exterior spaces. In TripAdvisor’s case, the building is located only a few feet away from a busy highway, so the main challenge was to determine whether glass upgrades were necessary at the four-story exterior curtain wall.
A conservative but expensive approach would have been to request the client to finance such an upgrade; instead, the design team performed a thorough study of the noise conditions at the site and clearly defined the background noise goals for the most stringent activity (in this case recording for broadcasting). Based on noise measurements at the site and on estimates of the sound levels blocked by different glazing constructions, it was determined that a standard insulated glass unit would suffice as long as lavaliere microphones would be used for speech recording/broadcasting. For all other uses, it was agreed that the highway noise would be low enough to blend in well with indoor activities.
How did the team arrive at that conclusion? By listening to auralizations of the sound levels based on a computer model of the building’s acoustics – a highly useful tool in the decision-making process.
As it relates to the interior of the building, an effective approach both in terms of acoustical results and cost is to avoid locating sound sensitive spaces directly adjacent to the atrium — and more importantly, directly accessed from this large and active space.
Finally, focus on controlling sound levels at the source: the level of activity noise created in the space. In a dining setup in TripAdvisor’s Forum, there can be 1,000 people all talking at the same time. In a presentation setup, loudspeakers will energize the whole space. If the atrium has mostly sound reflective surfaces (stone, glass etc.), these activities will create a cacophonous environment. Everyone in the room must shout to be heard over everyone else, leading to more noise, and thus escalating a viscous cycle of noise build-up.
The remedy: incorporate significant areas of sound absorptive treatment among the room finishes to control the reverberation of the space and consequently the sound buildup. Once again, carefully engineered solutions and close teamwork are paramount to ensure that such treatment is sufficient but not excessive, and that the sound-absorbing finishes blend harmoniously with the interior design of the space.
With acoustical design for atriums, the goal is a lively, energetic space — no one wants a “dead” sounding atrium or commons – but one that is comfortable and under acoustical control.
Markham, LEED AP, is the director of architectural acoustics at Acentech, and Pieleanu is a senior consultant in acoustics at Acentech. Based in Cambridge, MA, Acentech is a multi-disciplinary acoustics, audiovisual systems, IT and security design, and vibration consulting firm.