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Some sound advice.

Productivity can be improved in today's open plan offices.

A recent survey by Washington, D.C.-based American Society of Interior Designers (ASID) revealed that 71 percent of workers at five major companies with open plan offices thought noise interfered with their ability to effectively perform their jobs. Fifty-two percent of those same workers complained that noise levels in the office increased stress. Sound can negatively affect productivity, performance, and morale. Acoustical ceiling panels, wall treatments, and more can all be specified to ensure lower background sound levels. Here are some sound tips for improving acoustics in open plan offices:

Isolate the HVAC system.

The goal here is to isolate noisy heating, ventilating, and air-conditioning (HVAC) sources from activity spaces. Atlanta-based American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has established standards and procedures for rating the sound output of mechanical equipment. In addition, noise from air-handling systems can be limited by:

* Installing long duct runs.

* Increasing the duct size.

* Lowering the air flow velocity.

* Installing absorptive fiber glass duct liners.

* Creating noise diffusers or sound traps.

Muffle noise with ceiling tiles.

An absolute must to control sound in office spaces is acoustic ceiling tile. The ceiling area is, without a doubt, the largest open space in an office. Soft surfaces with little mass, such as fiber glass ceiling tiles, absorb some of the sound striking their surface and prevent it from being transmitted in the space.

The most common measurement is the noise reduction coefficient (NRC) - the ability of a substance to absorb sound. A tile with an NRC of .85 - the recommended rating in an open plan environment - means that 85 percent of the sound that strikes the tile is being absorbed.

In addition to reducing noise, another factor to keep in mind with ceiling tiles is their articulation class (AC). This measures a tile's ability to absorb speech frequencies that strike the ceiling at angles of 45 to 55 degrees, a typical level inside an open plan workstation with partial-height walls. An AC rating up to 200 is recommended.

Use caution with interior choices.

Typically, systems furniture used in open plan offices is evaluated based on an ability to block sound. Look for a sound transmission class (STC) rating of 20 or higher. In terms of partition heights, they should be designed and selected based on reducing the amount of sound traveling over and above the adjacent offices. As such, partitions should be tall, approximately 65 inches. As far as sound absorption is concerned, look for an NBC of .60, with a speech frequency and absorption average of .80 or more.

Absorb sound with carpet.

Carpet with ample padding, rather than tile or wood, is a good element of acoustical control for flooring as it absorbs airborne sound; reduces the surface noise generation of things, such as footsteps and furniture movement; and helps block sound transmission to rooms below. Consider carpet with an integrated polyurethane cushion, which has been shown to be significantly better at cutting noise levels by both absorbing sound and reducing transmission between floors in multistory buildings. For example, a concrete floor has an NBC of .015, a conventional carpet, .20, and a polyurethane cushion and carpet, .25.

Drown out distractions with sound masking.

Sound masking - the strategic placement of speakers to transmit a steady level of ambiguous noise into the environment - is another technique to control sound in offices. A well-designed sound system, mounted above the suspended acoustical ceiling, pointed upward on 12- to 16-foot centers, will produce a uniform hum similar to the sound made by an HVAC system. By taking into consideration the many aspects of good acoustical planning, tenants will be happier and more productive while working.

Eddy Scott is president of Ecophon Certain Teed, Montgomeryville, PA, an acoustical tile manufacturer.

Soundly Speaking: A Glossary

Following is a brief sampling of acoustics terminology to better understand sound reduction technology and to impress guests at parties.

* Articulation class (AC): Rates the listener's ability to understand the spoken word within a space, expressed as a decimal with 1.0 being perfectly understandable.

* Attenuation: The diluting or holding back of the energy of sound waves as they pass through a material. Materials are rated for their ability to prevent sounds from traveling through them.

* Decibel (dB): A unit to express difference in power. One decibel is about the smallest change the ear can detect.

* Frequency: Cycles per unit of time, usually expressed in hertz (Hz). The frequencies of audible speech lie in the range of 400 to 2,000 Hz - one cycle per second.

* Noise reduction coefficient (NRC): The ability of a substance to absorb sound.

* Reverberation: Persistence of reflected sound in a room after its source has stopped emitting sound.

* Sound transmission class (STC): A single number rating of a structure's efficiency to block airborne sound.
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Title Annotation:office noise levels
Author:Scott, Eddy
Date:Feb 1, 1999
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