Room Combine Logic with Mix-Minus Matrixing of Room Mics

In a large convention center or conference room, microphones may be routed to different speaker zones in a mix-minus configuration in order to reinforce microphones from one zone to another zone while minimizing the potential of acoustic feedback. When in a “mix-minus” configuration, microphones are routed to all zones except the zone in which the microphone resides, so the microphone level can be quite loud without creating acoustic feedback with the speakers directly overhead.

In most SymNet applications the mix-minus setup is straight forward and easily
accomplished using a Matrix Mixer module. However, when the convention center or conference room using mix-minus routing is part of a larger divisible venue, where two or more rooms can be combined and uncombined, then the logic for combining/uncombining the audio, the automixers, and control parameters (such as mute and volume) must be taken into consideration.

When no mix-minus routing is necessary, room combining is simple using SymNet’s Room Combiner modules. These modules will combine and uncombine the audio, automixers, and control parameters (gain, mute, sources selection) of 2 to 16 rooms with the push of a combine button.

Above: 2 Room BGM Automix Combiner

In the example above, when #1 Combine Button on the BGM Automix Combiner module is turned “on”, the audio, the automix, and the control parameters are shared between room 1 and 2. Any change to the room controls, such as BGM selection, volume, or mute, will affect both room’s controls. When the #1 Combine button is turned off, both rooms operate in a standalone fashion. This functionality is especially helpful when using a 3rd party control system, as no combine or uncombined logic needs to be added to the control system programming since SymNet will do all combine and uncombined logic automatically.

The limitation with the Combiner module in a mix-minus application is that each room has only a single room input and output for the local sources, whereas in a mix-minus configuration each room would have multiple speaker zones, each with their own unique mix of the microphones.

The solution is to use a Matrix Mixer and BGM Automix Combiner module
in tandem, using linked controller assignments, to create a mix-minus, room combine system where audio, automixers, and control parameters combine and uncombine.

The following example will create a two room system with combining/ uncombining capabilities and mix-minus matrixing of the mics. There are 12 microphones in room 1 and 8 microphones in room 2. Each room has 4 amp channels. For simplicity sake, this example includes only the processing associated with automixing, combining/uncombining capabilities, and mix-minus matrixing of the microphones. A real world design would also include dynamics processing and filtering/equalization at the input and output stages. Follow these simple steps to program a mix-minus, room combine, SymNet site file:

Step 1:
Build the site file such that Slave Gain-Sharing Automixers are used for all mics in the system. Separate Slave Gain-Sharing Automixers should be used for the mics located in each room.
Step 2:
The Automixer discrete outputs should feed the inputs of a matrix mixer module instead of using the Mix output.

Step 3:
Add a BGM Automix Combiner to the site file that can accommodate the number of combinable rooms in the venue – two rooms in this example. Wire the Chain output of the Automixers to their respective Chain input on the Combiner (blue wire). Wire up the Master out of the Combiner to the respective Master input of the Automixer.

Step 4:
Create the mix-minus configuration of the microphones using the Matrix Mixer user interface for the rooms when in the uncombined state Once the routing and crosspoint gains are configured for the individual uncombined rooms, right click the Connect Matrix and select Store “Connect Matrix” in Preset to store the matrix settings to a preset. This example uses preset 1 for the “uncombined/standalone” preset.

Step 5:
Create the mix-minus configuration of the microphones using the Matrix Mixer user interface for the rooms when in the combined state. Right click the Connect Matrix and store to a preset. This example uses preset 2 for the “combined” preset.

Step 6:
To stay organized, open the Preset Manager and rename the combine and uncombined presets accordingly. Then recall both presets, checking the matrix each time, to ensure they are correctly changing the matrix.

Step 7:
Add the following logic circuit using control modules: 1 button latched, 1 inverter, 1 dual preset trigger. The top Preset Trigger-1 should use the “combine” preset, the bottom Preset Trigger-2 should us the “uncombine” preset.

Step 8:
Open the 1 Button Latch and the BGM Automix Combiner and assign the same controller number to Button 1 and #1 Combine. This example uses controller #1.

Step 9:
On the BGM Automix Combiner assign the Volume fader for Room 1 and Room 2 each a unique controller number. This example uses 10 and 20.

Josh Carter

Josh Carter

Symetrix Technical Support Engineer

Document: 2014-01
First published: January 2014

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