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Sound masking raises the background level so most speech falls below it. Good masking offers a balance between privacy and comfort, says Jodi Jacobs, marketing director for Lencore.
"Sound masking is not meant to produce a cone of silence," Jacobs says. "It is meant to cover sound so it is not intelligible, so that content and meaning are not clearly understood and so are not as distracting."
Sound masking has the effect of making it sound like most of the people aren't there, says Moeller. The effect of sound masking increases with distance, so it doesn't interfere with talking in workspaces.
"For both comfort and effectiveness, the masking sound must conform as closely as possible to the desired masking curve and be consistent in volume," Moeller says.
Sound masking isn't the use of white sound, which is typically harsh, and scratchy. Instead, lower frequencies are added to make the sound more comfortable. The resulting "pink sound" is like the ocean, Jacobs says.
In addition to sound masking, open offices need barriers or materials to absorb and block sound, says Markham.
"Acoustical ceilings have to be designed to have high noise reduction coefficients (NRCs)," says Susan Raneri, ceiling product marketing manager at USG. Ceiling panels usually absorb about 70 percent of the sound (with .70 NRC). Panels that absorb 80 percent or more are better for open plans.
Some offices don't even use ceiling tiles. They have structures that show rafters, duct work, and so forth. "It looks like a warehouse and sounds like a warehouse," says Browne of Armstrong. "A longer reverberation time means you can hear someone 30 feet away."
What is needed to cope with distracting human voices is a balanced acoustical design, says Browne. The ceiling offers the largest surface area on which you can put absorbing material that will not be harmed. "You will instantly lower the volume and reverberation time, and the sound will die away more quickly," he says.
In situations where there is no ceiling, baffles that hang from the exposed structure can be used to absorb sound. New products include clouds and canopies, which are more decorative mini ceilings that hang from the exposed structure. They can be filled with ceiling tiles or constructed from materials that absorb sound from all sides. Of course, not all the sound will reach the ceiling. "The ceiling absorbs only what gets there," says Markham.
The acoustic aspects of office spaces have to be engineered just like everything else, says Herbert. "Most people think acoustics is just common sense. You do what everybody else does," he says. But each space is specific, and while the basics are similar, it is important to fine-tune carefully. "You have to engineer the whole acoustical system if you want to control distracting noise and provide privacy," Herbert says.
Maryellen Lo Bosco is a contributing editor for Building Operating Management.