Using Ceiling, Sound Masking Systems to Get Acoustics Right
Improperly diagnosing why employees can’t hear phone conversation — or why they hear too much of coworkers’ discussions — can lead facility executives to throw good money after bad.
Whether correcting acoustics problems in a conference or an open or private office, understanding the cause of employee frustration can guide the selection of technology to remedy concerns.
When there are acoustic problems in a conference room, unintelligible speech typically is blamed on the phone. When employees complain, office managers rush out to buy higher quality speaker phones — only to find the problem remains unsolved.
To the untrained ear, the speaker phone seems like a logical cause, but in reality, unintelligible speech is caused by reverberation and background noise. Reverberation refers to the sound bouncing around the room. It measures how long sound will bounce.
“In a conference, the sound is usually fine, but once there’s a teleconference, it’s hard to understand,” says Mei Wu, a principle with San Francisco-based Mei Wu Acoustics.
What the Ear Hears
While the human ear is not sensitive enough to pick up on the bouncing sounds, the speaker phone microphone is. The phone transmits voice sounds and background sounds along with reflective sounds. The result is muddled speech.
Kring Herbert, a principal with Ostergaard Acoustics in West Orange, N.J., says facility executives can screen conference rooms and offices for potential problems simply by spending a few minutes tape recording the sounds in the room. The playback will reveal what sounds speakerphone picks up.
“You’ll hear all this noise you didn’t hear before, but that’s what the microphone hears,” he said.
One quick fix might be to turn off the HVAC system and other controllable background sounds for the duration of the call.
Reverberation can be controlled by using acoustical ceiling tiles. “Acoustical ceiling tiles provide sound absorption and increase speech intelligibility,” Wu says.
Acoustic tiles can carry a variety of ratings. The NRC rating — noise reduction coefficient — measures the amount of noise a panel can absorb. The higher the rating, the more sound the tiles can absorb. Sound-absorbing wall materials can help, too. For example, fiberglass with a smooth texture is more acoustically friendly than standard drywall.
Unfortunately, issues with unintelligible speech don’t always disappear once the conference call is over and participants return to their workspace.
“In open offices, acoustics are very important,” Wu says. “If the ambient noise is too loud, you won’t hear anything. If it is too quiet, you’ll hear too much. It’s not good either way.”
Acceptable ambient noise is 35 decibels for open offices and 40 decibels for private offices.
Offices are full of distracting sounds. The most commonly cited sound distractions include ringing phones, including cell phones with custom ringers, employees who talk too loudly on the phone, coworkers who yell across the space and foot fall noises.
“The smaller space, the more noise you have,” Herbert says.
If the ceiling material is reflective, it will intensify sound problems. Installing acoustical tiles can reduce reverberation and increase sound absorption.
A key rating for open plan offices is AC — articulation class — which indicates how well ceilings and other interior products provide speech privacy in open offices. Open floor spaces require a high-performance ceiling with an AC rating of 180 to 210 to reduce reflected sounds.
Sometimes, the HVAC system can cover wayward sounds. If the HVAC system can’t cancel out the distracting noises, however, the space is a candidate for a sound masking system. Generally described as a nondescript white noise, sound masking will block distracting noises and improve speech privacy.
Most systems involve ceiling-mounted speakers. A good quality sound system can put out sound levels of 48 decibels without causing annoyance. A system that is too loud causes everyone to talk louder, adding to the noise problem.
Trendy office designs frequently incorporate exposed structural elements into the interior design. Concrete and steel beams are two examples.
“It’s been popular to have exposed structures, but exposed elements don’t have enough sound absorption and the place sounds noisy,” Wu says. “Sound bounces back and forth, and you can hear sounds from the other end of the office. The reverb is too long, and people will raise voices. But they still can’t understand each other because the sound is stretched out.”
This problem is particularly noticeable in converted warehouses, which weren’t designed for acoustical performance in the first place. High ceilings allow sound to travel farther above the source. Without sound-absorbing material, these large spaces can become reverberatory.
Ceiling systems are also available for open plenum spaces; the ceiling panels hang over selected areas of the space and are designed to reduce reverberation time and noise levels.
Lynn Proctor Windle is a contributing editor to Building Operating Management. She is a freelance writer who has written extensively about real estate.