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Author Topic: 70-volt speakers in series?  (Read 6293 times)

Mike Sokol

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70-volt speakers in series?
« on: March 30, 2016, 10:39:33 am »

I'm working on a restaurant sound system which has 4 ceiling speakers with 70-volt transformers driven by a little 35-watt TOA 70-volt mixer/amplifier. I was asked to add a 70-volt outside speaker with its own Atlas auto-transformer on the wall. When I tapped on to the existing 70-volt wiring by paralleling to the last speaker in the chain, my new speaker had very low volume and the paralleled speaker's volume dropped to nearly nothing, while all the other 3 speakers jumped up in volume a little bit. Some more testing showed that the original contractor had wired all 4 ceiling speakers in series, even though they each had transformer taps set at 3.5 watts. There was also a complaint from the client that the sound system wasn't ever loud enough even with the wall volume control on 10. I know the fix is to rewire all the ceiling speakers in parallel, but I'm curious as to why someone would wire four 70-volt ceiling speakers in series to begin with. Don't they know how 70-volt distribution works? Have any of you guys seen such a thing? Should I write an article about how 70-volt distribution works for PSW/LSI?
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Mike Sokol
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John L Nobile

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Re: 70-volt speakers in series?
« Reply #1 on: March 30, 2016, 10:58:34 am »

I'd really appreciate that. I have no experience with 70v systems but we have one in the hotel and I'm sure there will be a time when I'll have to look at it. All I've had to do so far is replace an amplifier.
So far all I know is what you said above. Wire in parallel not series.
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John Roberts {JR}

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Re: 70-volt speakers in series?
« Reply #2 on: March 30, 2016, 11:43:39 am »

There are numerous white papers on the WWW from just about every constant voltage system manufacturer.
=======
@ Mike, there is no good reason for wiring 70V speakers in series, if anything it makes the system less reliable (like old christmas tree light strings).

Arguably it uses less wire, but that is not the significant expense compared to labor, etc.

JR
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Lee Douglas

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Re: 70-volt speakers in series?
« Reply #3 on: March 30, 2016, 12:01:15 pm »

I'm curious as to why someone would wire four 70-volt ceiling speakers in series to begin with.

I'm trying to imagine not only why, but how someone would go to the trouble of wiring them in series.  If one were pulling a two conductor cable and only breaking one of the two wires to insert a speaker and using the other unbroken as a return, as long as the pair went by each speaker you should be able to correct it fairly easily.  Or did they really run a single conductor loop that goes by each speaker?  I'm really having a hard time wrapping my head around doing it so wrong! 

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Kevin Graf

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Re: 70-volt speakers in series?
« Reply #4 on: March 30, 2016, 12:21:08 pm »

Newer readers could start with this RaneNote:

Constant-Voltage Audio Distribution Systems
Dennis Bohn, Rane Corporation
RaneNote 136 written 1997; last revised 3/07

    25, 70.7 & 100 Volts
    U.S. Standards
    Just What is "Constant" Anyway?
    Voltage Variations -- Make Up Your Mind
    Calculating Losses -- Chasing Your Tail

http://www.rane.com/note136.html

**************************************
I remember decades ago, the was a great article about troubleshooting 70V systems. It was in either 'dB' or 'RE&P' magazine.
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Mike Sokol

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Re: 70-volt speakers in series?
« Reply #5 on: March 30, 2016, 12:23:40 pm »

I'm really having a hard time wrapping my head around doing it so wrong!

Yeah, me too. It was a single lay of 2-conductor / 18-gauge wire done in a single run from the amplifier, past each speaker, all the way to the end. So it didn't save an inch of wire to do them in series. They cut this feed wire and bugged each speaker onto it in series. Again, exactly the same labor and number of connections. It's all in how it was hooked up. I know it's all in series because as I changed the wattage tap on one of the speakers, all the other speakers would change as well, but in the opposite direction. And when I pulled a wire off of any single speaker, all the rest would die except for a little high-frequency bleed thru, which sounded exactly like an open leg in an XLR mic wire, for exactly the same reasons. Of course, this is some other sub-contractor who installed this, but I wonder how many other restaurants he's wired exactly the same way? Be on the lookout for this sort of crazy hookup.
« Last Edit: March 30, 2016, 02:00:57 pm by Mike Sokol »
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Steve M Smith

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Re: 70-volt speakers in series?
« Reply #6 on: March 31, 2016, 02:56:40 am »

Don't they know how 70-volt distribution works?
I think the previous text in your post answers this!


It was a single lay of 2-conductor / 18-gauge wire done in a single run from the amplifier, past each speaker, all the way to the end. So it didn't save an inch of wire to do them in series.
So it should be fairly easy to correct


Steve.
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John Roberts {JR}

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Re: 70-volt speakers in series?
« Reply #7 on: March 31, 2016, 10:15:00 am »

I have actually seen 70V outputs stacked in series to make higher voltage for very long feeds. One large race track, stacked up three output transformer windings in series to send 210V audio out over miles of wire.

JR
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Jason Lavoie

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Re: 70-volt speakers in series?
« Reply #8 on: April 01, 2016, 12:47:29 pm »

I'm working on a restaurant sound system which has 4 ceiling speakers with 70-volt transformers driven by a little 35-watt TOA 70-volt mixer/amplifier. I was asked to add a 70-volt outside speaker with its own Atlas auto-transformer on the wall. When I tapped on to the existing 70-volt wiring by paralleling to the last speaker in the chain, my new speaker had very low volume and the paralleled speaker's volume dropped to nearly nothing, while all the other 3 speakers jumped up in volume a little bit. Some more testing showed that the original contractor had wired all 4 ceiling speakers in series, even though they each had transformer taps set at 3.5 watts. There was also a complaint from the client that the sound system wasn't ever loud enough even with the wall volume control on 10. I know the fix is to rewire all the ceiling speakers in parallel, but I'm curious as to why someone would wire four 70-volt ceiling speakers in series to begin with. Don't they know how 70-volt distribution works? Have any of you guys seen such a thing? Should I write an article about how 70-volt distribution works for PSW/LSI?

Often people use the term (wired in series) as being the opposite of having a home run for each speaker.
I could very easily see someone saying "just wire them all in series" and an electrician or someone taking that literally.

Jason
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Joseph D. Macry

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Re: 70-volt speakers in series?
« Reply #9 on: April 01, 2016, 04:15:48 pm »

Often people use the term (wired in series) as being the opposite of having a home run for each speaker.
I could very easily see someone saying "just wire them all in series" and an electrician or someone taking that literally.

Jason
You mean someone using "series" when they mean "daisy-chained"?
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