PA Sound System through timing wire

There are multiple posts in the Data Communications forum. I'd suggest reading through them and make your own decisions.

You will almost surely receive false impulses on your timing lines due to the PA clipping. Find another solution.

There really is not enough information such as length of the timing cable to make an accurate determination of what is needed. James is 100% correct about running 70V speaker line over one of the cable pairs in your timing cable. However, there are two possible options that could be tried. One would be to send a "line level" signal (600 ohms)over one of the timing cable pairs up to a "line level" input to an amplifier up in your start area. From that amplifier you can feed each speaker with 70V from that start amplifier. If the signal is low, up at the start amplifier, then a 600 ohm amplifier may be needed. This would be your lowest cost option.

The other option would involve setting up a network between the finish and the start area using a set of DSL type adapters and using one of the cable pairs in your timing cable. You can then use a set of VoIP adapters to get the paging signal from the finish area up to an amplifier in your start area over that network set up. One other plus of this set up would be the fact that you would have a network connection up in your start area for other uses too. The downside of this set up is that it is not cheap to do and you also need an understanding of networking and VoIP equipment.

Steve

Don't do it!

Even before the wrong pulses, you might be in serious trouble with the law.
What you want to do is really far beyond any safety rules. Highly dangerous.
Do not mix a nontrivial voltage in a cable used with very low voltage equipment
such as timers and headsets.

Have a cable contractor suggest you the best way to do it.
Stocks are full of good not-so-expensive cables.