Sound Masking Part III
Can You Hear Me Now?
Perfecting Sound for Video and Telephone Conferencing Rooms

by Art Barkman

Have you ever spoken on the telephone to someone who is using a speakerphone? Chances are that the quality of the signal was not good. It may have sounded as though the person was speaking through a pipe – that “tin can” effect. Usually it’s not the phone, though; it’s the room.

The microphones in speakerphones are very sensitive, more sensitive than our ears. They pick up not only the first incidence of sound, but also the many successive reflections of that sound as it bounces from the hard surfaces within the room. You can’t hear it, but the microphones pick it up. The result is distortion.

This phenomenon is a smaller scale version of the effect of announcements we frequently hear in a large space such as an arena, railroad station, or airline terminal. You can hear, but it’s very difficult to understand. As one word is spoken (usually amplified and delivered through a loud speaker system), it reflects from the various surfaces in the space and you hear it again and again. Although at diminishing volume, it overlaps and interferes with the next word or syllable. Under extreme conditions, you hear much and understand little.

In a more intimate space, such as an office, the distortion is hardly perceivable to the people in the room. Their ears are not that sensitive. The microphones, however, do pick up those reflections and record and/or transmit them. That’s why the audio quality on your home video tape may not be what you heard when you recorded it. Again, it is not the equipment, but the room.

In a videoconference/telephone conference room this distortion is most always annoying to the listeners at the remote receiving location and may interfere with understanding. A reverberation time of less than 0.5 seconds is desirable, whereas times in excess of one second are typical of untreated rooms.

To correct this, many facilities add acoustical (sound absorbing) treatments to room surfaces. The walls are the most important surfaces to be treated as they permit multiple reflections. Application of acoustical panels above chair-rail height usually corrects the problem. The quantity of those panels, their performance (NRC) and placement is an important design consideration.

But ultimately, addressing more than just noise annoyance, taking the time to troubleshoot any sound problems upfront when designing an audiovisual room will help boost employee productivity in the space.


Art Barkman is president of Sound Management Group, Inc., Hillsborough, New Jersey. www.smg-corp.com