Lectrosonics FM875 - Manual (Page 9)

SYSTEM SETUP cont’d
4) If you have more than one transmitter on the same frequency, turn on only one transmitter at a time.
You cannot use the two transmitters at the same time with a single FM875. You will need to "alternate"
back and forth between the transmitters. Failure to do so will result in an obnoxious whining sound
from the system, and the audio will probably not be understandable.
5) Use the minimum volume that will enable everyone to hear. It doesn’t have to be loud to be heard.
Placing the FM875 in the back of the room works well in most instances, since this places the speaker
far enough away from the microphone to minimize feedback and close enough to the most distant
listeners to provide adequate sound coverage.
6) The FM875 should be elevated for best coverage. The unit should ideally be at least 2 feet higher than
the audience. For example, with an audience standing on flat ground, the number of people who can
hear clearly will double if you raise the unit from 5 feet above the ground to 7 feet above the ground.
See below for more detailed information on placement of the unit.
7) During actual operation, the FM875 should be aimed so that the sound from the speaker is directed
toward the audience and away from the microphone. This will reduce feedback problems. "Feedback"
is a loud squealing sound coming from the speaker when the volume is too high or the microphone is
too close to the FM875. Feedback is generally more of a problem when using lavalier (lapel) type
microphones than with hand-held or headset type microphones because the microphone is farther from
the mouth. See below for more details on feedback.
8) The standard FM-AV4 system includes an M140 cardioid lavalier microphone. This directional
microphone will minimize background noise and provide resistance to feedback when properly
positioned on the user’s body. Clip the microphone on the lapel or tie as close as possible to the
mouth.If the system is to be used outdoors or near an air conditioner duct, use the foam windscreen
provided with the mic. This will reduce "wind noise" caused by air movement across the microphone.
Refer to the Microphone Choices section on page 11 for optional microphones.
OPERATING TIPS
WHAT ARE THE CAUSES OF FEEDBACK?
Feedback (squealing) occurs when the sound from the speaker re-enters the microphone, comes back out
of the speaker again and re-enters the microphone, and so on. At a given distance between the
microphone and speaker, the sound can only be turned up to a certain loudness before feedback occurs.
Moving the mic further away from the speaker (or the speaker away from the mic) will allow a louder setting
of the sound system.
MAXIMIZING GAIN
1. Place the microphone as close to your mouth as is practical. This will increase the input level for the
microphone so that you are clearly picked up by the mic but background noise will be reduced.
2. Place the speaker (the main unit) as far as you can from where you’ll be speaking and in a position that
will cover your most distant listener.
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