On the Valcom the speakers use two pair. One pair for power , the other is to hookup to page port on Valcom unit. The Valvom page adapter alows you to hook up speakers to one of the 6 page zones. You hook a CO port of KSU to the input on Valcom page adapter. You either dial code to acces the CO port or put it on a key on the phones, after you access the CO port you dial a code to page a zone or all page.
The Valcom unit can feed each building with one pair (the page zone) and then install a 24 volt power supply in each building to power the speaker. I always run my speaker cable back to the IDF/MDF, that way you can change zones that speakers are in.
Each speaker as I said is self amplified. They come in speakers or horns and also different watts (5,10,15,30).
If you go to any Best Buy store there paging system is A Valcom unit using horns.
The only thing you want to make sure of: is that the paging speaker/horn are not to close to any phone that will be paging. This wil cause feed back and that loud squel everyone hates, but this is for any paging system.
Good Luck!!