Acoustics: Best to hear concerns during planning stage

By Denis Milsom  

Acoustic design is an integral part of planning commercial spaces. The time to set acoustics goals is early in the design phase — during concept or early schematic design — when the entire team can influence the outcome.

Approaching acoustic design in this way, instead of coming in after construction is under way or completed, also gives the team a chance to examine lease agreements regarding what the building owner provides, permanent changes that are made to the building, and the effects of construction noise.

During planning, the design team can designate spaces that will need attention, such as conference rooms or studios, and can determine the best floor plan to avoid acoustical problems, such as offices near elevator shafts or conference rooms located near machine rooms.

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Sloss Law, a law firm in Manhattan, shares its quarters with Cinetec, a multimedia company. The firms occupy 6,000 square feet on the fourth floor of a multitenant, 100-year-old wood-frame building. A redesign included a conference/screening room equipped with an impressive multimedia system for presentations. The team recognized that sound would be a problem for other office workers and for the tenants above and below.

To solve the problem, the conference room was acoustically isolated. The floor was built up and filled with lightweight concrete to create a sound barrier. The ceiling consists of two layers of drywall suspended from neoprene hangers to break sound transmission.

Studies prove that an office with acoustic levels appropriate to the work being done is more productive. Even at low levels, unwanted sounds can increase stress levels and impair communication and concentration.

In some cases, good acoustics are a legal necessity. According to the Health Insurance Portability and Accountability Act (HIPAA), medical information must be protected from being overheard by those other than the patient.

Almost every building has some acoustic problems. Some problems are a result of a building’s design, some are the result of poor construction, and some are caused by the users of the building. Although buildings can be acoustically treated after construction, it is generally more expensive and not as effective as designing the proper acoustics from the start.

Using structural and interior building components — such as the curtainwall, windows, door sand sealants — that have the optimal sound transmission class (STC) ratings for the acoustic goals of the occupant allows rooms to be isolated from ambient and outside noise. If the components have a rating that is too low, the building may not be suitable for its use. If the components have a higher rating than needed, the cost will be greater.

Similarly, the isolation of a room from outside noise is only as good as its weakest noise barrier. For example, high STC-rated walls are useless when combined with hollow-core doors and standard windows.

Construction methods also matter. Construction gaps are the easiest way for sound to pass from one room to the next. Sealing construction gaps is the least expensive method of improving acoustics, but many contractors view the practice as too time-consuming.

Common base-building sources of noise and vibration include elevator shafts, machine rooms, plumbing system noise, outside traffic and the HVAC system — either in the building, on the roof or outside the window. One of the most common scenarios is placing the high-level offices — those of the CEO and the company officers — on the top floor of the building. The view is great but the sound of the equipment on the roof directly above can be intolerable.

Other noise sources are smaller but can also exceed the desired background noise level of a room. These include high-intensity discharge lights, compressors in refrigerated drinking fountains, ballasts in fluorescent lights and transformers in exit signs. These noise sources are eliminated by specifying equipment with the proper sound ratings.

High sound levels are inherent to certain types of business. A medical office might need a magnetic resonance imaging system. Some small companies have their own printing equipment. And, occasionally, businesses require studio recording systems. All of these problems can be accommodated and designed for at the space-planning stage.

Some manufacturers may say that installing a single product will remedy every acoustic problem. But experience proves that a multipronged solution is usually more effective.

The first step in the planning process is to understand the users’ needs. This seems straightforward enough, but acoustic preferences are hard to define. People don’t really think about acoustics until they become a problem.

Exactly who is involved in the planning meetings depends on the complexity and size of the building. An acoustician should be an essential member of the design team. It is the acoustician’s job to establish and implement acoustic goals for the facility — goals that support the function, aesthetics and budget. A good architect or interior designer will get a general idea of the needs of the occupants during planning. But it is up to an acoustic consultant to explore these needs.

At Medtronic Inc., a medical technology company based in Minneapolis, such questioning helped define the company’s needs. Medtronic’s new campus, completed two years ago, is a multibuilding headquarters that includes a research center, a corporate conference center and administrative offices — a variety of acoustically complex spaces.

The biggest challenge was an atrium designed to serve multiple purposes, including accommodating large group meetings. Atriums are traditionally reverberant spaces, the effect of a lot of glass and tile flooring. But in this case, the noise was kept down by balancing the amount of glass with drywall. Hard-surface flooring was also balanced with carpet in certain areas. Ceiling coves were added to help capture and soften the area’s reverberation.

At the Medtronic headquarters, which is adjacent to a major highway, dimming the outside traffic noise was necessary to meet the company’s goals. The first order of business was to review a traffic noise study. Recommendations were made to upgrade the STC ratings of the curtainwall and glazing so that traffic noise wouldn’t be intrusive.

Probably the least expensive and most efficient way to reach a company’s acoustic goals is with careful space planning. Noisy equipment should be grouped in an area away from workstations; quiet spaces, such as conference rooms, should not back up to elevator shafts, lavatories or equipment rooms; areas of confidentiality should not be near the entry lobby; and theaters or presentation areas should not be adjacent to quiet areas.

Once the overall layout is defined, the elements of each area can be refined. This might include allowing sufficient space between cubicles and orienting them properly; keeping noisy equipment away from a hard wall or a corner where sound will be reflected back into the workplace; and facing the door of a private conference space away from the open office area.

Although creating a thoughtful floor plan is a good idea, it isn’t always possible to use the layout that is, acoustically speaking, most logical. Sometimes the conference room has to back up to the elevators because that is the only place it fits.

Another element that drives layout and, therefore, acoustic design, is aesthetics. Full-height, exposed ceilings are becoming more common; so are hard, sound-reflective surfaces, such as glass, concrete and stone. Some basic architectural shapes — domes, round rooms, rooms with concave surfaces, and square rooms — tend to focus reflected sound.

This sort of cutting-edge design makes spaces look cool, but they are not comfortable unless acoustics are considered. And that means investing in solutions, such as sound-masking systems to create background noise or special floor and ceiling configurations like those used at Sloss Law, to shield neighboring tenants from sound.

Denis Milsom is vice president and head of the acoustics department at Shen Milsom & Wilke in New York City.

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  posted on 8/1/2003   Article Use Policy

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