Shure SCM410E manual Inhibiting Gating for Unwanted Sounds, Loudspeaker Muting, ªFilibusterº Mode

Inhibiting Gating for Unwanted Sounds

MaxBus attempts to activate only one microphone per sound source. Muting a microphone channel prevents its audio from appearing at the mixer's output. However, the muted micro- phone still communicates with other mic channels via Max- Bus. A sound source picked up by a muted microphone will not activate other microphones.

Sound sources that may cause unwanted microphone chan- nel activation include:

•Heating, ventilation, or air conditioning systems

•A noisy fax machine or printer

•A squeaky door

•A paging system loudspeaker

•An audio teleconferencing return signal loudspeaker

The SCM410 can prevent these and similar sounds from acti- vating microphones as follows:

1.Place one microphone near the unwanted sound source. Connect that microphone's signal to a channel input,

Ðor Ð

connect the unwanted sound source directly into a channel input.

2.Mute that channel using the logic terminal (see Figure 24). To perform this modification internally on the mixer, refer to the Shorting Mute In to Logic Ground Internally paragraph in

the Internal Modifications section.

3.Adjust the channel gain control just past the level where un- wanted sounds do not activate other microphones in the system. If the channel gain is set too high, the other micro- phones may not be activated by the desired sounds. If set too low, unwanted sounds will continue to activate other mi-

crophones.

LOGIC

GROUND

M1

INHIBITING GATING FOR UNWANTED SOUNDS

FIGURE 24

Loudspeaker Muting

Some applications require a loudspeaker to be placed near each talker to provide audio reinforcement, or to permit tele- phone conversation or conference monitoring. Each loud- speaker can cause feedback unless it is automatically switched off when the talker near it speaks. To provide this function, con- nect the GATE OUT terminal of each channel to a separate loudspeaker muting relay (See Figure 25). Recommended re- lays are Radio Shack 275±248, Omron G2R-14-DC12 (Digi- Key number Z745-ND), Potter & Brumfield R10-E1Y2-V185 (Newark number 45F106), or equivalent.

NOTE: A diode across each relay coil is required to suppress inductive voltage spikes which may damage the SCM410.

An existing sound system using 24-volt relays can be used with the SCM410 without modification if the relay coil current draw is under 500 mA.

D = 1N4148

D D +

12 V

POWER

SUPPLY

±

LOGIC

GROUND

G1 G3

FROM

POWER AMP

LOUDSPEAKER MUTING

FIGURE 25

ªFilibusterº Mode

Normally, when several people talk, each microphone gates on so that no speech is missed. In ªfilibusterº mode, a micro- phone remains gated on until the talker pauses long enough for that microphone to gate off. No other microphone can gate on until that microphone gates off. This prevents talkers from being interrupted.

To establish filibuster mode, refer to Figure 26 and proceed as follows:

1.Perform the Mute to Inhibit modification as presented in the Internal Modifications section.

2.Connect all the MUTE IN pins together on the modified channel.

3.Connect all the GATE OUT pins together on the modified channels.

4.Connect the GATE OUT pin of one modified channel to the MUTE IN pin of another modified channel .

5.Turn the Last Mic Lock-On switch to OFF.

NOTE: To prevent high-frequency oscillation, do not wire a GATE OUT pin to a MUTE IN pin on the same channel unless the Mute to Inhibit modification has been made.

G1 G2 G3 LOGIC

GROUND

M1 M2 M3

ªFILIBUSTERº MODE

FIGURE 26

13