Polycom SoundStructure C16 Design Manual page 721

All participants that are seated at the table are well within the microphones pick-up ranges as shown in the
next figure.
Wireless Microphones
Wireless microphones are also commonly used in conferencing applications, particularly for presenters.
The advantage of wireless microphones is that they may be used anywhere within the room (depending on
whether in-room sound reinforcement is used with that microphone) and have the advantage that they are
usually closer to the local talker's mouth than a tabletop microphone. It is better to use a lavalier style of
wireless microphone than a hand-held wireless microphone to ensure that the microphone stays a constant
distance from the talker's mouth which will minimize the sound level variation to the remote participants in
a conferencing application. Wireless handheld microphones typically end up being placed on tables, used
as pointing devices, and end up in other situations that reduce the quality of the resulting audio signal. One
consideration with lavalier microphones is to ensure the users of the microphones understand where to
attach the microphone to minimize the occurrence of fabric being dragged across the microphone element.
There are different methods of transmission that wireless microphones use, ranging from analog
transmission over UHF or VHF frequencies to digital encrypted transmissions over a 2 GHz frequency band.
Considerations for choosing a wireless microphone include the signal bandwidth that is transmitted (narrow
or wide band), the latency introduced by the wireless microphone, the battery type and life (rechargeable or
not), reliable transmission distances, cost, freedom from interference, and whether it uses encryption to
secure the wireless channel.
Ceiling Microphones - Quality vs Convenience
In all applications, getting the microphone closer to the local talker results in a higher quality signal due to
improved signal-to-noise ratio (the local talker is louder compared to the background noise) and a reduction
in the amount of the multipath signal compared to the original signal.
In most conferencing applications there is a trade-off with the usage of a room, the location and
configuration of the furniture, and the maximum achievable audio quality. It is common for rooms with
movable furniture to not have permanently installed microphones on the tables. To accommodate this,
microphones are often moved away from the participants and placed in the ceiling. A consequence of this
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