|Sound Advice on Teleconferencing Room Acoustics
"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
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.
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.
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
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.
If you have acoustical or noise control design problems you
would like to discuss, feel free to call or FAX us any time.
3201 Ridgewood Drive
Columbus, Ohio 43026
For more information on... Angelo J. Campanella, P.E., Ph.D. (Principal)
Last updated 06-Jun-2005.
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