I would like to add to this post because I have a site just like the one described. Plant began as a 1500 x200 foot site with lots of noise. When I first went to site there were approx. 20 15 Wat horns
and and office overhead in hall ways. Every thing was cabled in conduit and using a 150 watt Bogen amp. Worked great and it was a 70 volt system.
I have had 3 major expansions and have been installing Valcom 5 watt horns. I like this application because the Valcom speakers/horns are
self amplified with local power supplies which mean you only need an audio pair cabled to that supply location.
Customer absoloutely loves it . I finally talked them into trunk level paging and a Valcom 2006 six zone page adapter.Now they can page only shipping and not wake everyone else up.
Since it is low voltage you can use Cat 3 cable and not concern yourself with building permits and inspections.
Try it, 7you will like it.
Have a great day, RBT