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Bring On Da Noise

Rattle, roar, or ruckus: With these hidden acoustical techniques, you'll never know it's there.

Sound is all around us; sometimes more than we want. Architects are in a position to control unwanted sound in the built environment, leaving visitors blissfully unaware of the din. The following is an abbreviated guide to the hidden acoustics all around us, often known only to a building’s design and construction team.

Few people realize, for example, that Boston’s InterContinental Hotel and condominium building on Atlantic Avenue is isolated on rubber pads. Not so many years ago, this site was a mud pit with massive concrete vent stacks rising 237 feet above grade to discharge air from the Central Artery tunnel. These vent shafts are now concealed inside the hotel. Some guest rooms are directly against the vent shafts, and the four-diamond hotel has very high standards for comfort.

To control the effects of vibration from the fans, the entire building is isolated from the foundation piles on rubber pads. The rubber alone cost over $1 million. Cavanaugh Tocci’s design of each pad had to take into account vertical loads, lateral loads, and seismic loads in all three axes. Large steel bolts and plates act as stops to limit deflection.

Many of us understand the fundamentals of noise reduction: Avoid gaps and leaks; use sound insulation in wall cavities; use multiple layers of gypsum board at walls where extra sound isolation is needed; employ thicker concrete floors to control sound and vibration. Beyond the basics, however, sophisticated (and expensive) techniques can control sound and vibration, easing the tumult of our daily lives.

Central Artery Tunnel vent shafts as seen from the Congress Street Bridge.  (Photo courtesy Cavanaugh Tocci Associates, Inc.) The vent shafts rise over 200 feet. (Photo courtesy Cavanaugh Tocci Associates, Inc.) The entire building is noise-isolated from the vent shafts.  At the base of every structural column, custom-designed rubber pads isolate the steel columns from the concrete foundation footings. (Detail view.) (Photo courtesy Cavanaugh Tocci Associates, Inc.) The entire building is noise-isolated from the vent shafts. At the base of every structural column, custom-designed rubber pads isolate the steel columns from the concrete foundation footings. (Overall view.) (Photo courtesy Cavanaugh Tocci Associates, Inc.)
Diagram of the InterContinental Hotel, showing the hidden vent shafts and the strategy of rubber isolation pads surrounding the shafts and at the foundation. Drawing by David Butler. Many high rise buildings have large, roof-mounted window wash rigs similar to the one pictured here, attached to the structural frame of the building. Operating the rig can cause disturbing noise and vibration in the building’s upper floors. (Photo courtesy Cavanaugh Tocci Associates, Inc.) Detail view of a typical window wash rig, at the connection to the track. The metal-to-metal connection can transfer noise and vibration via the support column, to the building. (Photo courtesy Cavanaugh Tocci Associates, Inc.) Detail of custom-designed rubber pads at Atlantic Wharf. These rubber pads isolate this window wash rig from the building’s structure, and therefore prevent noise and vibration from transferring to the occupied floors. (Drawing by Greg Tocci, Cavanaugh Tocci Associates, Inc.)
The Peabody Essex Museum courtyard offered different acoustic challenge: creating a tranquil acoustic environment in a very large space with stone floors, and large areas of glass. Here, a combination of finish material and HVAC vent choices created an acoustic environment akin to being outdoors. It allows for multiple conversations to occur simultaneously without interfering with one another or getting too loud. (Photo by Timothy Hursley, courtesy Safdie Architects. Notes by Timothy Foulkes.)      

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The window wash rig at the new Atlantic Wharf office tower offers another custom-designed sound isolator system. High above street level, window washers work from a suspended platform. Their window wash rig moves around the building perimeter on a steel rail-and-column system at the roof. Below the roof are top-floor executive offices. In some buildings, moving these rigs on their steel rails creates distracting noise in offices below. At Atlantic Wharf, rig movements are almost inaudible because of a sophisticated system of rubber pads that isolate the track from the support columns. Each isolation point must be designed for vertical loads with and without the rig at that location, lateral loads in both directions, and uplift loads from the rig.

One look at the soaring atrium at the Peabody Essex Museum would lead most visitors to expect a noisy, reverberant space: The high ceilings, stone floors, and large glass areas are a potent combination for sound. But the acoustics are well controlled, with sound qualities more like an out-door courtyard. Even more surprising, there are no obvious acoustic finishes.

One of the atrium’s most important acoustic features, paradoxically, is background noise. The ventilation system was designed and adjusted to produce a low-level white noise, to mask the last 20 to 30 decibels of reverberation without interfering with speech. The jet nozzle air diffusers create this sound, and their velocity is carefully set to create the desired amount of noise.

The finish materials — sunshade fabric, brick walls, and ceiling panels at the adjacent balconies — also contribute. Each brick absorbs a small amount of sound; collectively the effect is significant. The sunshade fabric, covering a large surface area, works on a similar principle. The balcony ceiling panels — which absorb 85 percent of the sound that reaches them — are well-camouflaged, designed to look like smooth plaster.

Acoustic consultant Alban Bassuet of Arup wanted the space to be moderately reverberant. There should be some reflections to bring the space alive but still provide for easy communication. He used a computer model to calculate acoustic values and to simulate the sound of the space. Creative acoustic mitigation was wholly integrated with Moshe Safdie’s architecture.

Project credits

InterContinental Boston
Architect: Elkus Manfredi Architects
Structural Engineer: McNamara/Salvia, Inc.
Noise Isolation Design: a joint venture between Cavanaugh Tocci Associates, Inc. (Sudbury); Acentech (Cambridge); and Wilson Ihrig & Associates (San Francisco)
Lead Consultant for Vibration Pad Design: Greg Tocci, Cavanaugh Tocci Associates, Inc.

Atlantic Wharf
Architect: CBT Architects
Structural Engineer: McNamara/Salvia, Inc.
Noise Isolation Design: Cavanaugh Tocci Associates, Inc.

Peabody Essex Museum
Architect: Safdie Architects
Acoustic Design: Arup (Alban Bassuet, project manager)