Dialing down the decibels at home, at work and dining out

(Roger K. Lewis For The Washington Post)
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By Roger K. Lewis
Saturday, February 13, 2010

Nature's assaults are never-ending, but humans and what they build also cause environmental disturbances, one of which is unwanted noise -- intrusive noise, ugly noise, discomfiting noise. We have the knowledge and techniques to cope with unwanted noise, but sometimes we don't or can't use them.

Consider your house or apartment. Your dishwasher may progress noisily through its cycles, or your refrigerator compressor may crank up intermittently, interfering with television, music or conversation near the kitchen. Other than buying quieter appliances, the only fix is to increase the distance between appliances and your ears -- sound intensity is inversely proportional to the square of the distance between the sound source and your ear. For example, doubling the distance cuts sound intensity by a factor of four.

Forced-air heating, ventilating and air-conditioning (HVAC) systems produce unwanted noise from fans and fan motors, air flowing rapidly through ducts and registers, and vibrating sheet metal. Despite concealment behind ceilings, bulkheads, floors and walls, and despite putting equipment in basements, attics or mechanical rooms, HVAC noise frequently intrudes into living spaces.

Although today's state-of-the-art mechanical equipment is quieter and more energy-efficient, air conditioning still must move through ductwork and registers. Using larger ducts (to reduce air speed) and acoustic insulation in and around ducts and equipment can cut HVAC noise.

If you live in an apartment or townhouse sharing walls and floors with abutting units, noise generated by neighbors can be especially annoying. The problem is twofold: Inconsiderate people and inadequate acoustic separation. You may solve the first problem through diplomacy. Solving the second problem is tougher, as it stems from improper design.

Adequately reducing sound transmission between requires walls and floors with special properties. Substantial mass using concrete or masonry diminishes noise. And incorporating sound-deadening panels in steel- or wood-framed structures can reduce noise transmission.

Sound-absorbing insulation within walls and floors also helps. Equally critical, there must be no unsealed joints, cracks, holes or other penetrations through walls and floors because sound, like moisture, travels readily through the smallest openings.

But even with acoustically solid construction, high-impact noise is hard to block out completely. Low- and high-frequency vibrations generated by spirited dancing, stiletto heels, children jumping off beds or wall-mounted speakers can be heard even through many inches of concrete.

Two other annoying noise sources may afflict your home, as they do mine: snoring and aircraft. According to my wife, ear plugs are reasonably effective for coping with the former, but depending on where you live, intrusive aircraft noise may be a problem day and night. For example, my house is near the Potomac River in Northwest Washington, directly below the radio-beam-guided flight path to and from Reagan National Airport.

And helicopters regularly fly over the river at low altitude. In spring, summer and fall, when we are frequently outside, the whine of jet engines and chop of helicopters can stop conversations. Inside in winter, the noise is still audible but somewhat muffled thanks to double-glazed, tightly sealed windows and doors.

Offices, like homes, can be acoustically compromised, especially when numerous workers and their desks are arrayed in a single space or in open cubicles rather than separate offices with doors. Ringing phones and loud conversations intrude and distract. Fortunately, audio headsets, sound-absorbing carpeting, and acoustically treated ceilings and partitions help make the auditory ambience of workplaces tolerable.

Less tolerable, at least for some, are increasing numbers of restaurants and bars where ear-piercing noise levels make conversation difficult and sometimes almost impossible. But hyper-noisy restaurants are created purposely. The marketing and design assumption is that most patrons -- especially young adults -- prefer eating, drinking and socializing in informal, crowded spaces characterized by a 90-decibel din.

A few key design attributes make a space loud and resonant when filled with people: large room volume; high ceilings; and hard, sound-reflecting finishes on floors, walls and ceilings. Concrete, masonry, metal, glass, tile and hardwood can look good, but they suck up almost no sound.

Creating a gentler acoustic ambience in an eatery requires dissipated sound energy, which calls for large spaces divided into smaller spaces, lower ceilings and, most important, interior finish materials that scatter and absorb sound. This is accomplished with carpeted floors; walls covered with layers of fabric, tapestries or acoustic panels; upholstered seating; and acoustic ceiling treatments.

Aural sensitivity varies greatly from person to person. Perception of and response to sound depend on not only sound frequency and intensity, but also context. The sound of someone next to you in a movie theater unwrapping a candy bar may be more noticeable and annoying than noisy household appliances, airplanes flying overhead or loud bistros.

Thus the challenge for architects, engineers and acousticians: Everyone hears things a little differently.

Roger K. Lewis is an architect and a professor emeritus of architecture at the University of Maryland.


© 2010 The Washington Post Company

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