What’s the difference between Audible Silence and Selective Silence?
Selective silence I’ve seen most commonly referred to on Simplex systems, where they can silence a 2 wire horn-strobe so that just the strobes are running when signal silence is pressed. It’s all about the circuitry of the alarm and diodes and stuff that I don’t quite understand!
Audible silence, requires a four-wire horn/strobe to work and each have their own dedicated NAC. So, NAC 1 would most commonly be silenceable (for the horns). Strobes would be hooked up NAC 2 and set on nonsilenceable.
All speaker/strobes are four wire because they need separate wiring for the audio and strobe… although I’d be interested to see if selective silence would be possible someday on speaker/strobes.
I’ve never heard of selective silence on a Simplex system, as Simplex does not make 2-wire horn/strobes. (Smartsync does not count.)
Audible silence is when audible alarms can be silenced but visual signals cannot. One way of achieving this is by having audible appliances on one NAC and visual on another. If audible and visual appliances are combined (like a 2-wire horn/strobe that is not Simplex), then selective silence essentially pulses them to synchronize the horns and strobes, and gives a shorter pulse if only the strobe should be activated at one point.
For example, if in code-3, then the NAC would be pulsed like this:
Long
Long
Long
Short
(Repeat)
If silenced, it would only be short pulses.
This article clears up some of the code-related myths of audible silence: