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Author Topic: 70 volt auxilliary zone has low volume  (Read 33323 times)

Matt Carr

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Re: 70 volt auxilliary zone has low volume
« Reply #10 on: January 06, 2011, 06:44:13 pm »

Sidney Pilien wrote on Wed, 05 January 2011 19:52The speaker wire size sounds correct. The system runs higher voltage-low current  at high impedance for long wire runs and less heat so increasing the wire size may worsen the problem.


Sidney, why would it be worse?  Is it because in a sense I'm switching it from a high impedance to a low impedance system if I use 16awg wire, therefore, making the amp work harder to push current through that much wire?  I've always been taught that undersized wire meant more resistance and more heat which is exactly what you don't want your amp to have.
I certainly don't consider myself a pro sound guy so I'm just asking the question.
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Lee Buckalew

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Re: 70 volt auxilliary zone has low volume
« Reply #11 on: January 06, 2011, 08:29:51 pm »

Matt,
Larger wire is not worse for a 70 volt (or 25 volt or 100 volt) system.  Different rules are applicable that allow for the use of a higher gauge (smaller conductors) but it does not require the use of higher gauge wire.


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Lee Buckalew
Pro Sound Advice, Inc.
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Frank DeWitt

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Re: 70 volt auxilliary zone has low volume
« Reply #12 on: January 06, 2011, 10:28:32 pm »

There is a lot of confidence that nothing is wrong (nothing was changed, it just got quiet)  This reminds me of the joke we told while working on cars.  Has it got gas, yes, spark, yes compression, yes,  GET OUT OF THE WAY it must be running. Of course it never was.

So, something changed, or the gain structure is messed up.  If it was me, I would disconnect the speakers and put one 8 ohm on the 8 ohm output and listen Sounds good at any volume, amp and mixer and gain structure are OK  Doesn't, then I would disconnect the input and try a input from my tone generator or I-pod to check the amp.  

Once you have a good output then reconnect the speakers.  Still bad, Take one down and try that, if it is OK reconnect, and try to brake the line in the middle, ETC until you find it.  BTW  I know everyone says nothing changed, but is there one speaker that is nice and loud?  perhaps someone decided to help out and added or changed a speaker and put one in with no transformer. That will mess it up.

It looks like you are down to divide and conquer.

Frank

Jonathan Johnson

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Re: 70 volt auxilliary zone has low volume
« Reply #13 on: January 07, 2011, 12:08:56 am »

So what would the effect on the system be if an individual speaker or its transformer experienced a short-circuit failure, creating an extreme low-impedance situation, but not low enough to trigger protection in the amplifier?

This could be tested for by disconnecting all the speakers and connecting them one by one until the system dumps out. To make things quicker, you might be able to disconnect groups of speakers.

Just a thought to throw out there.
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Sidney.Pilien

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Re: 70 volt auxilliary zone has low volume
« Reply #14 on: January 07, 2011, 12:09:50 am »

Matt Carr wrote on Thu, 06 January 2011 18:44

Sidney Pilien wrote on Wed, 05 January 2011 19:52The speaker wire size sounds correct. The system runs higher voltage-low current  at high impedance for long wire runs and less heat so increasing the wire size may worsen the problem.


Sidney, why would it be worse?  Is it because in a sense I'm switching it from a high impedance to a low impedance system if I use 16awg wire, therefore, making the amp work harder to push current through that much wire?  I've always been taught that undersized wire meant more resistance and more heat which is exactly what you don't want your amp to have.
I certainly don't consider myself a pro sound guy so I'm just asking the question.


Like telephone lines, like balanced lines, the smaller wire=higher line (not speaker) impedance= longer runs.

It's like this: blow air through a 1/4" straw 20' long and another through 1" at 20'.
The amount of air(current) required to flow through the wider straw (lower resistance or impedance) is higher than the smaller (higher impedance) at the same rate and requires more effort thus producing more heat. And the air will travel farther w/the smaller straw(smaller lines).

This is not your typical 8 ohm amp in that it is designed for long runs typically paging systems and so lowering the size increases current and thus heat, reducing the life of the amp since it remains in use for the entire business day.

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Frank DeWitt

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Re: 70 volt auxilliary zone has low volume
« Reply #15 on: January 07, 2011, 09:36:11 am »

At audio frequencies bigger wire is always better.  There is a point where making it bigger doesn't improve things enough to be worth more money, it but it never hurts.  

A 70 volt system doesn't need very big wire because the voltage is high and therefor the current is low but big wire won't hurt it.

Ray Rayburn who has a extensive resume including designing audio systems for the US congress has published a couple of spread sheets to help select the best wire for speakers.

for low impedance systems.
http://www.soundfirst.com/LZ_DF_calculator.zip

And for constant voltage systems.
http://www.soundfirst.com/CV_DF_calculator.zip

His web site is here
http://www.soundfirst.com/technical.html

Frank

Matthias Heitzer

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Re: 70 volt auxilliary zone has low volume
« Reply #16 on: January 10, 2011, 10:39:32 am »

If there really is a short somewhere in the line, bigger wire could make things worse, but that's the only situation i can think about.

If we are talking about AC, the electrons aren't acutally travelling through the wire, they just move back and forth.
That's a good thing, because they are as slow as 0,3 mm/s.

Let's take Sidney Pillen's straw and fill it with water.
Now we fill our mouth with orange juice and pump the juice through the water-filled straw. What will come out of the straw? It's water, and if we beginn to draw back the liquid fast enough, the juice won't drip out of the straw. (if we exclude that water and juices blends in real life)
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Gary Creely

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Re: 70 volt auxilliary zone has low volume
« Reply #17 on: January 10, 2011, 11:05:18 am »

Matthias Heitzer wrote on Mon, 10 January 2011 10:39

If there really is a short somewhere in the line, bigger wire could make things worse, but that's the only situation i can think about.

If we are talking about AC, the electrons aren't acutally travelling through the wire, they just move back and forth.
That's a good thing, because they are as slow as 0,3 mm/s.

Let's take Sidney Pillen's straw and fill it with water.
Now we fill our mouth with orange juice and pump the juice through the water-filled straw. What will come out of the straw? It's water, and if we beginn to draw back the liquid fast enough, the juice won't drip out of the straw. (if we exclude that water and juices blends in real life)


Ok, I need to just say all this back and forth nonsense about cable size is just very unlikely to have anything to do with the problem at hand. If it was 18ga or 10ga it should not be causing a dramatic loss of volume.
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Gary Creely
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Matt Carr

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Re: 70 volt auxilliary zone has low volume
« Reply #18 on: January 10, 2011, 01:40:18 pm »

Well, it has been interesting and informative reading all the replies. Thank you.
I discovered Saturday when I disconnected the speaker run at mid point I was able to identify a problem with the first section. I discovered one speaker connected to the 25V side of the transformer in an old office that's not currently being used. The church didn't even know it was in there. Once it was connected to 70V everything worked great, even on the 22awg wire.
Thanks for all the feedback.
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Brad Weber

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Re: 70 volt auxilliary zone has low volume
« Reply #19 on: January 10, 2011, 03:28:51 pm »

Glad you found the problem and took care of it!
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Brad Weber
muse Audio Video
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ProSoundWeb Community

Re: 70 volt auxilliary zone has low volume
« Reply #19 on: January 10, 2011, 03:28:51 pm »


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