70 V system with multiple locations for amp connection

Teiresias

New Member
Joined
Nov 29, 2017
Location
Washington State, USA
I'm building up a meeting room AV system and had a quick question. Due to a number of factors we will be using ceiling mount speakers in the drop ceiling and our 70V amp will be in a mobile lectern or cart with a snake of wires that will connect it to a wall jack panel. I've put in 70V systems before in this way, but I was asked if it was possible to have multiple wall jacks that the cart or lectern could be plugged into at various locations around the room to help reduce the length of the cable snake and keep it from being a trip hazard if running across the room. I have yet to have wire to more than one wall jack and was wondering if this would cause any problems or need to be wired in a specific way for a 70V system. There is no chance that multiple wall jacks would be in use at the same time as there will only be one cart and amp in the room. I figured I could just wire all the 70V speakers in parallel like normal and then whatever speaker is nearest to the jack can also be wired to that particular wall jack. I wasn't sure if the extra wall jacks and wiring to them will cause any issues.

Thanks,
Teiresias
 

MNicolai

Well-Known Member
Fight Leukemia
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Mar 30, 2008
Location
Sarasota, FL
It's bad form to have multiple locations to drive the same speakers from but functionally it will work to parallel the various inputs together. I would label the jacks accordingly to caution users to never have more than one location plugged in. Someone very well may try to run two carts in that room 5 or 10 years from now. Things get upgraded/replaced/abandoned, and what looked like it was impossible on Day 1 becomes inevitable by Day 600.

Ideally, the amplifier would be installed permanently in the room or in the ceiling, and the cart would connect into the speakers just by plugging an XLR into the wall that feeds the amp. Stewart Audio makes some great, plenum-rated 70V amplifiers you can do this with.
 

Teiresias

New Member
Joined
Nov 29, 2017
Location
Washington State, USA
It's bad form to have multiple locations to drive the same speakers from but functionally it will work to parallel the various inputs together. I would label the jacks accordingly to caution users to never have more than one location plugged in. Someone very well may try to run two carts in that room 5 or 10 years from now. Things get upgraded/replaced/abandoned, and what looked like it was impossible on Day 1 becomes inevitable by Day 600.

Ideally, the amplifier would be installed permanently in the room or in the ceiling, and the cart would connect into the speakers just by plugging an XLR into the wall that feeds the amp. Stewart Audio makes some great, plenum-rated 70V amplifiers you can do this with.
Excellent Point. I certainly don't want them getting in trouble in the future by hooking up multiple amps to the same speakers and blowing the whole system. There isn't much room for the amp outside of a cart/lectern, but I'll look at the amps you recommended and I may be able to cram it up in the drop ceiling (as there really isn't anywhere else to put it) and then just put a line mixer in the lectern for volume control. Good to know this is possible, but I'll see if they have the budget to avoid it.

Thanks,
Teiresias
 

Craig Hauber

Member
Joined
Nov 6, 2016
Location
Plentywood MT, Grenora ND
Excellent Point. I certainly don't want them getting in trouble in the future by hooking up multiple amps to the same speakers and blowing the whole system. There isn't much room for the amp outside of a cart/lectern, but I'll look at the amps you recommended and I may be able to cram it up in the drop ceiling (as there really isn't anywhere else to put it) and then just put a line mixer in the lectern for volume control. Good to know this is possible, but I'll see if they have the budget to avoid it.

Thanks,
Teiresias
But you don't have to have the amp in the same room. You can go hundreds of feet with your XLR input line, and you aren't as limited in speaker line length when running 70V. You could put the amp in an equipment closet or I-T room along with all the other equipment in your facility.
They also make self-powered ceiling speakers for commercial applications -some models even run off a form of POE so the power supply can be remote and you don't have to worry about finding power above the drop-ceiling and the code implications of having gear sitting in the plenum space.