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Author Topic: 70-volt speakers in series?  (Read 7401 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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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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John Roberts {JR}

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Re: 70-volt speakers in series?
« Reply #10 on: April 01, 2016, 05:38:32 pm »

You mean someone using "series" when they mean "daisy-chained"?
One of the bad things about wiki is no technical editor....

Quote from: wiki
The term daisy chain may refer either to large scale devices connected in series, such as a series of power strips plugged into each other to form a single long line of strips, or to the wiring patterns embedded inside of devices.

Seriously, while the outlet strip line cords may be in series, the loads are all connected in parallel.



Whenever someone say's "daisy chain" I ask them what exactly do they mean. Apparently daisy chain has become popularly used to describe digital data ring networks.

The best way to think about this is "never connect speakers in series". That was easy.

JR
 
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Mike Sokol

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Re: 70-volt speakers in series?
« Reply #11 on: April 02, 2016, 01:38:01 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.

I had a long conversation with the design engineer for the company acting as the overall contractor of these installs. He said they've installed this exact same sound system at 170 identical restaurants around the country (fast food joints, remember?) and this is the first one that was miswired. The sub-contracted crew that wired this site had already been fired weeks ago from a bunch of other things they goofed up. I'm guessing the new guy on the crew got to climb around in the ceiling while the supervisors stood outside and smoked. And yes, this will be a simple fix once we get the additional time approved. We just have to go to each speaker and reconnect in parallel instead of series.
« Last Edit: April 04, 2016, 09:52:34 am by Mike Sokol »
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Jason Lavoie

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Re: 70-volt speakers in series?
« Reply #12 on: April 04, 2016, 09:23:20 am »

Apparently daisy chain has become popularly used to describe digital data ring networks.

And that gets to another level of confusion, because device to device, the wiring IS in parallel, but then the overall configuration is a series ring

Jason
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Joseph D. Macry

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Re: 70-volt speakers in series?
« Reply #13 on: April 04, 2016, 02:59:24 pm »


The best way to think about this is "never connect speakers in series". That was easy.

JR

Okay, just to be contrary, I have a bass amp with a 4x10 cabinet (Fender Bassman Ten combo). The four 8-ohm speakers are wired series-parallel (two series pairs, which are connected in parallel) to make a 8-ohm system.
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John Roberts {JR}

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Re: 70-volt speakers in series?
« Reply #14 on: April 04, 2016, 03:39:03 pm »

Okay, just to be contrary, I have a bass amp with a 4x10 cabinet (Fender Bassman Ten combo). The four 8-ohm speakers are wired series-parallel (two series pairs, which are connected in parallel) to make a 8-ohm system.
That is a musical instrument cabinet, where accuracy is not paramount. DF for tube amps is not a strong point.

JR
[edit] and don't forget the Bose 901... 9 speakers in series [/edit]
« Last Edit: April 04, 2016, 03:42:17 pm by John Roberts {JR} »
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Mike Sokol

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Re: 70-volt speakers in series?
« Reply #15 on: April 04, 2016, 04:00:42 pm »

Okay, just to be contrary, I have a bass amp with a 4x10 cabinet (Fender Bassman Ten combo). The four 8-ohm speakers are wired series-parallel (two series pairs, which are connected in parallel) to make a 8-ohm system.

That is the correct way to wire 8-ohm speakers in a 4x10 bass cabinet. The original Bose 901 cabinets had 9 speakers that were 8 ohms each wired in series-parallel. And you can figure out the next number of speakers that will form systems with the same impedance of a single speaker by the squaring the number. So you can do the same trick with 4, 9, 16, 25, and 36 speakers, etc.... But there's always exceptions to every rule. I had four of the Ampeg SVT 8x10 cabinets back in the 80's, and they had 32-ohm speakers. So you wired all 8 of them all up in parallel to get a 4-ohm cabinet.
« Last Edit: April 04, 2016, 04:03:36 pm by Mike Sokol »
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John Roberts {JR}

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Re: 70-volt speakers in series?
« Reply #16 on: April 04, 2016, 06:16:50 pm »

That is the correct way to wire 8-ohm speakers in a 4x10 bass cabinet. The original Bose 901 cabinets had 9 speakers that were 8 ohms each wired in series-parallel.
Yes at first, but after they started making boatloads of these they tooled up a 0.9 ohm driver that they could wire all 9 in series.
Quote
And you can figure out the next number of speakers that will form systems with the same impedance of a single speaker by the squaring the number. So you can do the same trick with 4, 9, 16, 25, and 36 speakers, etc....
Any here old enough to remember the Sweet 16 speaker project? (4 strings of 4 drivers in one huge box). Back in the 70's I built a 16 driver box, and a friend built a 25 driver box... Loud for the '70s home hifi, but the small drivers in a sealed cabinet tuned for >100Hz needed a ton of EQ to make decent bass, and no amount of EQ would cover the top octave properly with those midrange drivers.
Quote
But there's always exceptions to every rule. I had four of the Ampeg SVT 8x10 cabinets back in the 80's, and they had 32-ohm speakers. So you wired all 8 of them all up in parallel to get a 4-ohm cabinet.
Without getting too esoteric musical instrument cabinets are different animals with other important considerations (like intentional cabinet interactions, etc)..

JR
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Steve M Smith

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Re: 70-volt speakers in series?
« Reply #17 on: April 05, 2016, 08:40:40 am »

But there's always exceptions to every rule.

Like the WEM cabinets I had with two 12" 16Ω speakers wired in parallel with an engraved plate on the back marked 6Ω.

Or the six small speakers in a Peavey CL-2 which make up 8Ω.  I can't remember if they are series/parallel or just all parallel.  Possibly 3 x 5.3Ω in series twice with each string in parallel.


Steve.
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Craig Hauber

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Re: 70-volt speakers in series?
« Reply #18 on: April 06, 2016, 11:43:18 am »

I had a long conversation with the design engineer for the company acting as the overall contractor of these installs. He said they've installed this exact same sound system at 170 identical restaurants around the country (fast food joints, remember?) and this is the first one that was miswired. The sub-contracted crew that wired this site had already been fired weeks ago from a bunch of other things they goofed up. I'm guessing the new guy on the crew got to climb around in the ceiling while the supervisors stood outside and smoked. And yes, this will be a simple fix once we get the additional time approved. We just have to go to each speaker and reconnect in parallel instead of series.

Are they actual 70V speakers with transformers?
You can wire a bunch of normal 8-ohm ones in series to hook them directly to a 70V line with no matching transformers needed.
-I can't remember the exact quantity off the top of my head but 7 will get you around 100W on the line. (50-ohm at 70.7V)
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Mike Sokol

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Re: 70-volt speakers in series?
« Reply #19 on: April 14, 2016, 04:48:12 pm »



Whenever someone say's "daisy chain" I ask them what exactly do they mean. Apparently daisy chain has become popularly used to describe digital data ring networks.

The best way to think about this is "never connect speakers in series". That was easy.

JR

And here's how they connected speakers to the main trunk line. As you can see, they just cut the one side of the line, and connected the speakers in series. Waco eh?
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Mike Sokol
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Re: 70-volt speakers in series?
« Reply #19 on: April 14, 2016, 04:48:12 pm »


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