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70/100V speaker / amp questions...

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John Roberts {JR}:

--- Quote from: Richard Hedderly on December 31, 2020, 11:41:13 AM ------------------------------------------------------------------

Hey Kevin,

This is certainly a "trying to understand what they had / have got" scenario.

Some background.

The church is over a hundred years old and when I went under the floor near where there the speaker cable feed is, there was a label around the cable of 70V.

Now, the current sound system is circa mid 1990s. That's not to say they didn't have a old 70V distributed system before in the 60's until then and reused the speaker cables.

I'm new to the PA side of things. I wanted to make sure that there wasn't a hidden setting somewhere that needed to be enabled.

Given they only have one set of FOH speakers and a smaller stereo pair in a side room, I'd prefer to use this Behringer which has no mention of 70/100V setup.

So if it's a case that there are non 70/100V systems and 70/100V systems, that's great.

It points to that they did reuse the old 70V speaker wire and that the 90s kit is in fact a non 70/100V system.

Would love your take on that.

Best wishes

--- End quote ---
It is still unclear what hand you are dealt.

The behriger nx4_6000 seems like a lot of power for a church instal.

70/100v "constant voltage" systems are confusing because they are neither constant voltage or always 70V. I won't attempt to deliver a full tutorial, there are several easy enough to find on the WWW. A few high points, these constant voltage systems are popular for industrial background music installs. They generally standardize on a relatively high voltage output and load that high voltage feed with higher impedance speaker loads, often using step down transformers. Any number of these modest power 70v speaker loads can be added in parallel as long as you don't exceed the total amplifier power output.

If you use your 4 channel high power amp, it is simple enough to drive 4 low impedance speakers individually. 

To answer your speculation about driving low impedance speakers through 70V speaker wiring, one intended benefit from 70V systems is lower current in the speaker wires meaning you can get away with cheaper, thinner gauge wire. Also 70V wiring would probably put all speakers in parallel unless designed to support different zone. You can use thinner wire to drive low impedance speakers, just don't tell your audiophile friends. They won't catch fire, and you seem to have power to burn...

Good luck.


Kevin Graf:
Most modern pro amplifiers (300 Watts and larger) can drive most 70 Volt systems, without any modifications or special transformers.

Lee Douglas:
It would appear that unless somebody modified it with a transformer, the SM112IV and the rest of that line were 8 ohm speakers:

Richard Hedderly:

--- Quote from: Erik Jerde on December 31, 2020, 12:04:07 PM ---It would probably be helpful to know exactly what equipment is currently installed and (as beat you can determine) how it is hooked up.  The suspect 70v line may be appropriate for high voltage audio or it may not.  Knowing what the cable is will help with that.  For instance you can run 70v systems through a building on category cable and often be fine.  A high voltage system would have major problems doing that.

--- End quote ---

As it is hooked up, there are two FOH Yamaha S112IV-OAK speakers and their + - cables go down under the floor and come up next to the console desk into a speakON 4 pole panel socket. A speakON 4 pole plug into it then splits into two speakON 2 pole plugs that plug into the back of the Harmon Spirit Soundstation 600 analogue mixer / amp. [Manual picture attached]

There isn't a distributed speaker system installed around the church for announcements. I can't find any specific transformers for any 70/100V lines. It looks like all the power the FOH speakers need comes out the back of the mixer and that the label on a cable that says 70V is of a long gone legacy install.

Richard Hedderly:

--- Quote from: Lee Douglas on December 31, 2020, 02:44:28 PM ---It would appear that unless somebody modified it with a transformer, the SM112IV and the rest of that line were 8 ohm speakers:

--- End quote ---

Right, that's the manual I have and to double check, I got a ladder and it says it on the back of the speakers as well.


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