Topic: Hal, your opinion please

[MrGemini]

I'm laying out a new paging system for a 260 K SQ. Ft warehouse.
I,m thinking 6 zones each with a 100 watt Amp using 70 V horns.
My question is will I be OK with running the line level from my page out on the PBX
throughout the warehouse?
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Thanks, Wayne

[telemarv]

I'm not Hal (TG) but I'm curious why would you run PBX line out through out the building. It only needs go to the rack of amplifiers.

[Marc Haycook]

I'm not Hal (TG) but I'm curious why would you run PBX line out through out the building. It only needs go to the rack of amplifiers.

I think he's referring to the line LEVEL out of the PBX, not a physical trunk port. I've been known to be wrong, but that's how I read the post.

Oh... and I too am not Hal.

[silversam]

Full Disclosure:

I'm not Hal either.

However I ran Line Level Microphone connections several thousand feet at JFK airport. Microphone connections should be run on shielded cable and not run along with speaker wiring.

Sam

[hbiss]

I'm Hal. As Sam says you should be fine. You do want to use a balanced line however and depending on the PBX the page output may or may not be. This may require a balun or other unbalanced to balanced converter possibly at the page port and at the amp input if it doesn't have a provision for a balanced input, however those are relatively inexpensive. I'm assuming that the reason for your question is because the amp will be that distance away from the PBX? Ever consider moving the amp and running speaker wire?

-Hal

[MrGemini]

Sorry guys, just got in.
Marv, (and others), the reason is to have the amps mounted remotely within a central area of the zone they will be handling.
It makes troubleshooting easier and if you get a short on a speaker run it doesn't take out the whole system.
Separate amps in a rack would do the same thing but then a few zones I would need to run several thousand feet
 of speaker wire before I hit the 1st speaker in that zone. Also I already have 25 and 50 pair IDFs throughout the warehouse
I was hoping to use for the input.

[telemarv]

So your power amps are spread thoughout the building to minimize long speaker runs.

If you are splitting the PBX page output into 6 zones you definitely need a zone page adapter at the pbx. Running that length over a twisted pair will have a lot of line loss.

[hbiss]

So it's not just one amp as I first thought. Are you using a zone controller or are you thinking if bridging all the amp inputs together off the PBX page port? How many amps?

Also I already have 25 and 50 pair IDFs throughout the warehouse
I was hoping to use for the input.

I assume then that you plan on using a pair on the existing cabling for line level audio?

-Hal

[silversam]

Can you use an unshielded pair in a house cable for a line level mic feed? Wouldn't you run the risk of picking up interference from existing voice pairs?

Sam

[MrGemini]

Hal, 5 to 6 100 watt amps.
Yes, i was thinking of using existing pairs but the more I think about it
a separate 22/2 shielded would probably be better.
I'll have to give it more thought tomorrow.

[jknichols]

I'm not HAL either, but if you want to use house pairs, I'd use something like Bogen's WMT-1A transformer to go from unballanced line level to 600 ohm balanced twisted pair. (actually, I used one of them in the other direction - to go from a 600 ohm page output to a Line input on the amp, but they should work in either direction. If you are tying 6 of them together on one zone output, you may need some kind of amplified spliter.

[hbiss]

I've run line level on a pair in a 25pair for maybe a couple of hundred feet without problem. No interference with other pairs but put your toner probe within a foot of the cable and you hear the audio program loud and clear. I think a lot has to do with the twist of the cable and how well you balance the feed. Probably less than CAT3 might be a problem. It doesn't cost anything to give it a try though on a long run before you start running shielded twisted pair. I also agree that you will need a line driver to handle all those bridges. Something like THIS at the PBX location will also take care of the unbalanced to balanced conversion. The amps you select should have balanced line level inputs.

-Hal

[MrGemini]

In an amplified speaker application I know you can run the page output all around the world,
usually in the same UTP as the power until distance mandates remote power supplies.

My original thought was to use 70 V horns and have the amps in the field and either daisy chain the page output or star configure it.
 One problem that comes to mind immediately is any interference picked up on the page output, (amp input) will be distributed
throughout the whole system. But maybe not if I use a bridge. 
All the IDF are fed with no less then cat 3. 
as you said, I think a balanced system is the only way to go, probably with STP cable for the page output/ amp input.
I don't want to be fighting old problems on a new system, might as well do right from the start.
That's why I'm looking for input here. 
---------------------------------
Thanks, Wayne

[hbiss]

My original thought was to use 70 V horns and have the amps in the field and either daisy chain the page output or star configure it. One problem that comes to mind immediately is any interference picked up on the page output, (amp input) will be distributed throughout the whole system. But maybe not if I use a bridge.

By "bridge" I meant taps off the daisy chained line pair for each amp, the same way we use the term in this industry. Not a distribution amp that takes an input and provides separate line level outputs which you would run individually to supply each amp- although that would be a better choice if you could do it. In the least it would make troubleshooting easier since a short in the line level line would kill the whole system.

In an amplified speaker application I know you can run the page output all around the world,
usually in the same UTP as the power until distance mandates remote power supplies.

Quite true, the only limiting factor is voltage drop on the pair that carries the DC power. Just goes to show that you can use the existing UTP but there have been instances of noise attributed to that method. But you are only talking about 5 or 6 locations, not a building full of amplified speakers with wiring that can be anywhere.

-Hal

[tonyburkhart]

seriously thinking about changing my sig to "I'm not Hal, but..." :)