Speaker level controlled by rheostats.

[Donald]

Helping with the sound at a small church. Currently there are two front speakers and two rear speaker in the ceiling. The front has a rheostat to control it's level and the rear has the same. It's not really stereo as most of the sound is from the speaker's microphone.

I am not sure how the rheostats play into the impedance of the speakers being fed by a power amp.

I am thinking of getting rid of the rheostats and putting the front speakers on one channel of the power amp and the rear on the other channel and use the gain control for each channel in the power to get the level the same whether sitting in the front or back.

 

[eljefino]

Smart idea. Those line-level rheostats by design have to soak up a bunch of wattage.

 

[ctechbob]

It could possibly be a 70 volt system, which work a little differently than what normal systems do.

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[brianl703]

It could be a 70V system. Check for transformers at the speakers to be sure.

 

[Donald]

It could be a 70V system. Check for transformers at the speakers to be sure.

Well they are pretty high up in the ceiling. I have the manual for the power amp (QSC model 1200) and it looks like a normal system for 4 or 8 ohm impedance speakers

 

[mk378]

Is there a mixing board? Installing one at the pulpit or somewhere in the room would allow a live user to control the levels easily as needed.

 

[brianl703]

Well they are pretty high up in the ceiling. I have the manual for the power amp (QSC model 1200) and it looks like a normal system for 4 or 8 ohm impedance speakers

Might want to pull the volume controls out and see if they're designed for 70V. You can use a normal power amp with a 70V system by having it feed a transformer.

 

[AndyB]

A QSC 1200 will drive a 70V speaker system with out using a transformer.

 

[Donald]

So short of climbing into the ceiling of the church and looking at the speakers how can I confirm if it's a 70V setup?

I thought 70V systems where you had a PA system with many speakers throughput a building with many floors and rooms. This is 4 speakers in the ceiling of a church. Power amp is at the back with the mixing board.

 

[mk378]

If you're going to make any decisions on a project, you need to know what you have to work with.

How many wires leave the amplifier to drive the speaker system? If its only two, this probably is configured as a 70 volt line with the line splitting at the wall volume controls-- which you should also inspect.

If there are two pairs of speaker wire, that is probably independent circuits for the front and rear, you could investigate that by disconnecting one at a time.

Remember that if you touch it you own it though.

 

[AndyB]

70 line volt systems are used for long speaker runs. Pretty good possibility the system is configured that way.

 

[Donald]

I should say the speakers are speaker enclosures and 8" wide and 3' high. Each has 3 or 4 six inch speakers.

Four enclosures total.

I need to go through the audio related wiring in general as a lot of old unused wiring. Lots of cables for microphone and we have gone to wireless microphones.

I own all the technology at this church camp. That kind of work is my contribution. Better than painting or raking leaves.

 

[meep]

Partsexpress will have a lot of parts available for repair or replacement. The 70v system, if you have it, has its place - efficiency over long runs with controls for maintaining impedance. They also have a very active forum with folks that know a lot of this “esoteric” stuff well.