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Author Topic: 70v speakers on 8/4/2 ohm amp  (Read 13125 times)

David Allred

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70v speakers on 8/4/2 ohm amp
« on: July 27, 2015, 12:16:17 pm »

"The integrated 70V ‘matching transformer’ allows multiple speakers to be
connected together without danger of overloading the power amplifier
due to impedance drop."

Is this Yorkville speaker description blurb saying that I could connect a bunch to a QSC RMX2450, PLX 3102, or other similar Crown, Peavey, or other standard amp?  Doesn't seem right.  Please advise.

David
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John Roberts {JR}

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #1 on: July 27, 2015, 12:26:24 pm »

"The integrated 70V ‘matching transformer’ allows multiple speakers to be
connected together without danger of overloading the power amplifier
due to impedance drop."

Is this Yorkville speaker description blurb saying that I could connect a bunch to a QSC RMX2450, PLX 3102, or other similar Crown, Peavey, or other standard amp?  Doesn't seem right.  Please advise.

David

There are many decent white papers on the WWW describing "constant voltage"  or 70V sound distribution systems so I won't repeat the whole story. Short version is that nominal amp output voltage is normalized for 70VAC which is generally high voltage swing for a modest sized power amp, while some high power amps get up there in voltage swing.

The 70V loudspeakers are likewise scaled up in impedance to pull only modest watts of power from a 70V feed.

So yes a bunch of 70V speakers could be hung off a conventional amp without hurting the amp, but they may not get very loud if the amp doesn't put out anywhere near 70V nominal voltage.

JR
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David Allred

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #2 on: July 27, 2015, 12:59:44 pm »


, but they may not get very loud if the amp doesn't put out anywhere near 70V nominal voltage.

JR

I have an Excel spreadsheet that converts watts to volts at a given load. 
How do I determine the load presented at the amp by the "x" number of 70v speakers connected? 
The spreadsheet also lists V RMS and V Peak.  Is V RMS the critical value for this?  As you can tell this is from a limiter calculator.

thanks
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John Roberts {JR}

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #3 on: July 27, 2015, 01:09:19 pm »

I have an Excel spreadsheet that converts watts to volts at a given load. 
How do I determine the load presented at the amp by the "x" number of 70v speakers connected? 
The spreadsheet also lists V RMS and V Peak.  Is V RMS the critical value for this?  As you can tell this is from a limiter calculator.

thanks
There are different flavors of 70V speakers. They will generally offer a power selection or be set for a fixed power.  So a 70V speaker that is tapped for 5W, means you can work backwards from that 5W number to determine effective impedance load at 70V to make that many watts of power. When you determine the impedance of each speaker then you need to calculate the parallel impedance.

It will be easier to add up the power from all the 70V speakers together then calculate that one effective impedance.

Or just use a 70V amp... (Peavey used to sell a step-up transformer called auto-match so you could convert a normal amp to 70V).

JR




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David Allred

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #4 on: July 27, 2015, 01:32:20 pm »



It will be easier to add up the power from all the 70V speakers together then calculate that one effective impedance.



JR

So if I need to change the number of 70v speakers it alters the load to the amp.  Therefore, it changes the needed specs of the amp.  Are 70v amp so much more expensive because of demand, electronics, or something else?
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John Roberts {JR}

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #5 on: July 27, 2015, 01:40:24 pm »

So if I need to change the number of 70v speakers it alters the load to the amp.  Therefore, it changes the needed specs of the amp.  Are 70v amp so much more expensive because of demand, electronics, or something else?

70v amps are more expensive than what???

Fixed install amps for constant voltage systems are generally pretty inexpensive...

While the modern value MI amps are getting obscenely cheap (I am so old I remember when 1$/Watt was cheap)  8) ... compared to the cheapest MI amp the install amp with an output transformer may be a few $ more, but they are NOT expensive amps, far from it.

JR
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Ivan Beaver

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #6 on: July 27, 2015, 01:54:59 pm »

So if I need to change the number of 70v speakers it alters the load to the amp.  Therefore, it changes the needed specs of the amp.  Are 70v amp so much more expensive because of demand, electronics, or something else?
With any amp-the more speakers you add, the lower the impedance.

Basically think of a 70V system as a high impedance system.

A 1 watt tap is roughly equal to 5000 ohms
10 watts is 500 ohms
100 watt is 50 ohms

600 watts into 8 ohms is 70V
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David Allred

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #7 on: July 27, 2015, 01:57:22 pm »



 (Peavey used to sell a step-up transformer called auto-match so you could convert a normal amp to 70V).

JR

Still do.  For $125-$150, it seems like an option.
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Mac Kerr

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #8 on: July 27, 2015, 02:07:08 pm »

Still do.  For $125-$150, it seems like an option.
With any amp-the more speakers you add, the lower the impedance.

Basically think of a 70V system as a high impedance system.

A 1 watt tap is roughly equal to 5000 ohms
10 watts is 500 ohms
100 watt is 50 ohms

600 watts into 8 ohms is 70V

To expand on Ivan's comment, just make sure you have an amp capable of 600W into an 8Ω load. When you have close to 600W of 70V speakers on the amp you can start worrying about more amps.

Mac
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David Allred

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Re: 70v speakers on 8/4/2 ohm amp
« Reply #9 on: July 27, 2015, 02:23:37 pm »

70v amps are more expensive than what???

Fixed install amps for constant voltage systems are generally pretty inexpensive...

While the modern value MI amps are getting obscenely cheap (I am so old I remember when 1$/Watt was cheap)  8) ... compared to the cheapest MI amp the install amp with an output transformer may be a few $ more, but they are NOT expensive amps, far from it.

JR

Maybe I am missing something.  QSC CX series 70v amp 400w is $1770 MAP.  QSC RMX series 400-500w (depending on preferred rating) @ 8 ohm is only $750 MAP.
Granted, as the number of speakers added increases, the 70v amp's cost per speaker goes down.  If using many low wattage ceiling speakers the 70v can work out really cheap.  If using 100w taps on larger format speakers the 70v is really expensive. 
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Re: 70v speakers on 8/4/2 ohm amp
« Reply #9 on: July 27, 2015, 02:23:37 pm »


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