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Author Topic: 70.7v system puzzling me  (Read 1628 times)

Nathan Walker

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70.7v system puzzling me
« on: January 17, 2008, 11:13:37 pm »

I've just recently added a speaker and volume knob to a 70.7v system. We wanted to connect an older 70.7v speaker in the kitchen with it's own volume knob so that music could be played throughout the fellowship hall.

After installing the volume knob which is an Atlas Sound AT10, I realized that the speaker in the kitchen was way to soft from 1-9, and then when I switched from 9 to 10, the kitchen speaker picked up a great deal of volume while the fellowship hall speakers lost a great deal of volume.

For the sake of time, lets assume that all speakers are 15watt and the amplifier is rated at 60watt.
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Gary Creely

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Re: 70.7v system puzzling me
« Reply #1 on: January 17, 2008, 11:44:43 pm »

We need alot more info than that to help you out. How many speakers total ? What are they tapped out at? Are they tapped at 15 watt or is that the max, because that is pretty much for a 70v system if there are many speakers and a 60 watt amp.. Give us some more actual specifics about how this is all laid out.
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Gary Creely
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Nathan Walker

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Re: 70.7v system puzzling me
« Reply #2 on: January 17, 2008, 11:53:24 pm »

Ok, well I've got two speakers in the front of the fellowship hall that are normally used as mains (the system was installed before I had arrived and I still don't quite understand why they had these two speakers on a 70.7v system). They have little adjusters at the back of the speakers for wattage, when adding the new speaker I dropped the wattage of the speakers from 30 to 15 each.

The speaker that was installed in the kitchen is actually the original from an old paging system back in the 70's or something. It has a transformer in it and was wired as common and 4ohm according to the screen type on the transformer itself.

There are three speakers total, two tapped out at 15 watt and the third is an older existing speaker that was recently reconnected before we decided to get a volume knob for it.
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Gary Creely

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Re: 70.7v system puzzling me
« Reply #3 on: January 19, 2008, 10:32:54 am »

Are you sure the old speaker in the kitchen is actually 70v, and not 100v? It sounds like it is responding like a non- 70v speaker does when you hook it up to a 70v system. I would just try a new 70v speaker, they are very in-expensive.
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Gary Creely
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Nathan Walker

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Re: 70.7v system puzzling me
« Reply #4 on: January 19, 2008, 12:41:02 pm »

Would replacing the transformer make a difference?
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Mike Sessler

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Re: 70.7v system puzzling me
« Reply #5 on: January 22, 2008, 02:23:49 pm »

A transformer will cost you $5 plus shipping. A new speaker will cost $10-20 including a transformer. Better to just get a new one than use a 30 year-old paging speaker. Parts Express has a good selection of 70v stuff.

FWIW...
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Mike Sessler
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Brad Weber

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Re: 70.7v system puzzling me
« Reply #6 on: January 22, 2008, 05:20:10 pm »

Nathan Walker wrote on Thu, 17 January 2008 23:53

The speaker that was installed in the kitchen is actually the original from an old paging system back in the 70's or something. It has a transformer in it and was wired as common and 4ohm according to the screen type on the transformer itself.

Which side is wired as common and 4 Ohm, the speaker side or the incoming/amp side?  Or did you mean 4 Watt?  The Kitchen speaker might even be a Valcom type speaker that takes a line level audio input and is self powered via incoming DC, they were fairly common then as part of phone based paging systems.  It might help if you could get any model numbers or a more complete description.


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Brad Weber
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Chris Juried

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Re: 70.7v system puzzling me
« Reply #7 on: January 25, 2008, 10:13:31 pm »

Do you have an Impedance Bridge? If so, simply express the total tapped wattage by utilizing the forumla V^2/R=P

Where V^=70.7*70.7=4998.49 for simplicity we can utilize 70*70=4900

     R= Reading off your Impedance Meter in Ohms (Measure of  Resistance)
     P=Power Tapped in Wattage






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Chris Juried
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Re: 70.7v system puzzling me
« Reply #7 on: January 25, 2008, 10:13:31 pm »


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