How do I create a Fire Alarm Mute?

Will Fraser

How do I create a Fire Alarm Mute?

Interfacing Soundweb London with a fire alarm system is a common application. This is typically achieved by connecting a dry normally closed relay from the fire alarm system to a Control Input on a Soundweb London device. If the connection fails or the fire alarm system is triggered, the Control Input to the Soundweb London will change state. Programming the desired functionality can be achieved by several different methods. These methods generally fall into two categories - System Mute or Alternate Audio Source. Which method you use is at the discretion of the local fire authority, but usually it is the System Mute variation.

System Mute

In this example we have placed an N-Input Gain at the output of the signal chain. The Master Mute in this object will be used to mute all the audio in this device. If you have multiple outputs on multiple devices, make sure to link all the Master Mutes to create a Fire Mute Link Group. For more information on creating Link Groups, view the guide on the BSS Audio User Groups or download from the BSS Audio web site.

Remember: When using controls in a Link Group, any one of the controls can be attached to a port in order to control the entire Link Group.

Open the default control panel for the N-Input Gain.

Open and expand the Design Tree to show the control ports of the device we are connecting to. Note: This does not have to be the device containing the N-Input Gain; it can be any device on your network.

Once the Design Tree is expanded to the correct location, pin it open so that it will remain on the desktop.

Navigate back to the N-Gain default control panel. Click and drag the master mute from the control panel over to the Design Tree and drop it on the Control Input that we are connecting to the Fire Alarm system.

This will open a dialog box for configuring how this control will be attached to the port. There are three options - Direct Action, Inverted Direct Action and Toggle Action. You will use Direct Action or Inverted Direct Action depending on whether the closure from the Fire Alarm system is normally open or normally closed.

Ideally in this type of application the Fire Alarm system would be providing a dry contact in the closed condition that would fault to the open state during alarm. If this is the case, you will choose Inverted Direct Action when attaching the mute button to the port. If the system goes into alarm, the cable comes unplugged or the wire is cut, the system will mute, indicating a problem or alarm.

Alternate Source Selection

In the example file, we have placed 2x1 Source Selectors on each output signal chain. These need to have only two states (the two states of the control port), so make sure the “Allow None” property of the Source Selectors are set to “No”. The first input on this Source Selector is the audio signal from the Fire Alarm system. The second input of each Source Selector is the audio signal for each zone.

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