Shure SCM810 User Manual page 12

Inhibiting Gating for Unwanted Sounds
As described in the Operating Principles section, MaxBus at-
tempts to activate only one microphone per sound source. Mut-
ing a microphone channel prevents its audio from appearing at
the mixer's output. However, the muted microphone still commu-
nicates with other mic channels via MaxBus. A sound source
picked up by a muted microphone will not activate other micro-
phones.
Sound sources that may cause unwanted microphone channel
activation include:
•
A noisy fax machine or printer
•
A squeaky door
•
A paging system loudspeaker
•
An audio teleconferencing return signal loudspeaker
The SCM810 can prevent these and similar sounds from activat-
ing microphones by taking the following steps.
1. Place one microphone near the unwanted sound source. Con-
nect that microphone's signal to a channel input,
connect the unwanted sound source directly into a Mic/Line
channel input.
2. Mute that channel using the logic terminal (see Figure
16—Channel 1 is muted).
3. Adjust that channel's gain control just to the level where other
microphones in the system do not activate for the unwanted
sound. If the channel gain is set too high, other system micro-
phones will be difficult to activate for desired sounds. If set too
low, unwanted sounds will continue to activate other micro-
phones.
M1
INHIBITING GATING FOR UNWANTED SOUNDS
FIGURE 16
Loudspeaker Muting
Some applications require a loudspeaker to be placed near each
talker to provide audio reinforcement, or to permit telephone con-
versation or conference monitoring. Each loudspeaker can
cause feedback unless it is automatically switched off when the
talker near it speaks. To provide this function, connect the GATE
OUT terminal of each channel to a separate loudspeaker muting
relay as shown in Figure 17 (Channels 1, 3 and 5 shown modi-
fied). Recommended relays are Omron G6B-1174P-US-DC12,
Potter & Brumfield R10-E1Y2-V185, or equivalent (available
through Digi-Key and Newark Electronics).
NOTE: A diode across each relay coil is required to suppress in-
ductive voltage spikes which may damage the SCM810.
An existing sound system using 24-volt relays can be used with
the SCM810 without modification if the relay coil current draw is
under 500 mA.
—or—
LOGIC
GROUND
D = 1N4148
D D
G1
LOUDSPEAKER MUTING
"Filibuster" Mode
In normal operation, when several people talk, each microphone
gates on so that no speech is missed. In "filibuster" action, a mi-
crophone that is gated on prevents other microphones from gat-
ing on. Once a microphone has gated on, other microphones
cannot gate on until the talker has paused long enough for that
microphone to gate off. Thus the person talking has the floor and
cannot be interrupted.
To establish this function, first perform the internal Mute to "Inhib-
it" modification (see Internal Modifications). Then connect all the
MUTE IN pins of the modified channels together, all the GATE
OUT pins of the modified channels together, and the GATE OUT
pin of one modified channel to the MUTE IN pin of another modi-
fied channel (see Figure 18—Channels 1, 2 and 3 modified).
Turn the Last Mic Lock-On switch (SW702, position 2) to off.
NOTE: To prevent high-frequency oscillation, do not wire a chan-
nel's GATE OUT pin to its own MUTE IN pin unless the Mute to
"Inhibit" change has been made.
JUMPER
"FILIBUSTER" MODE
Inhibit Function
See Internal Modifications.
12
+
D
12 V
POWER
SUPPLY
–
LOGIC
GROUND
G3 G5
FIGURE 17
G3
G1 M1 M3
G2 M2
FIGURE 18
FROM
POWER
AMP
LOGIC
GROUND