"Teleconferencing" is a buzz word these days along with "Videoconferencing" which adds slow-scan TV for better group communication. With the rising use of satellite communications, this will become the rule rather than the exception. This thrust leads to many attractive and convenient conference rooms. Good speech intelligibility is vital. However, the teleconference room is now part of the audio circuit. This demands adequate acoustical treatment of all room surfaces. The slightest echo will undermine the ideal that "everybody understands everybody else". Duplex Designing the conference room to meet client expectations hinges on the critical need of "duplex" telephone systems. Your ordinary telephone is "full duplex", where anything either party says is heard by the other whether or not the other party is speaking. However, if the receiver speaker volume is turned up so that many can hear and also speak, the duplex system breaks down. Either they cannot all hear, or cannot all be heard, or the system squeals in a feedback frenzy fostered by room echoes. "Half-duplex" circuits are a fix for this problem where the receiver is shut off during voice transmission and vice versa. But "dead time", while the half-duplex computer decides whether a talker is done speaking, increases in rooms with insufficient sound absorption. This conversation time stretch-out undermines rapid repartee. Echoes Reverberant echoes will fool the half-duplex computer into thinking a talker has not yet finished speaking and will also introduce an undesirable "hollow" sound into the transmitted audio. Reverberation reduction requires significant sound absorbing material. Since teleconferencing started in higher management echelons, early teleconferencing rooms were "designer showcases" of panelling and window surfaces, all of which inspire sound echoes. Cost-effective sound absorbent finishes such as ordinary acoustical tile were shunned. In contrast, soft furniture and drapes make ideal teleconferencing room finishes. The reverberation time must be very short, with sound absorbent treatment spread over a significant portion of all surfaces. Thin carpet is not a very good sound absorber for its area share, but it does eliminate distracting floor noises from foot and chair scuffing. Noise Most offices and conference rooms are too noisy and too reverberant to serve as a teleconferencing room. A quiet library stack area would be better. The HVAC background noise must be not more than NC-25 (about 30 dBA). More noise will require higher half-duplex microphone threshold settings making it necessary to speak in raised voices, which can be tiring. Another consideration is the location and pickup pattern of the microphone(s). Since a conference table is a gathering place for papers, documents, maps and general object movements, it is a noisy place indeed for a microphone! That works for an individual speaker-phone, but often fails in practice except for hands-folded conferences. So the favored place for pickup microphones is often below the ceiling over the conference table. Summary The teleconferencing room is to be designed as a package with the aid of a professional acoustical consultant, especially when an upscale interior design is required. An A/V consultant or knowledgeable A/V equipment supplier can then designate an effective teleconferencing electronics package to the client's satisfaction.
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Campanella Associates
For more information on... Angelo J. Campanella, P.E., Ph.D. (Principal)
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