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Author Topic: distributed speaker question  (Read 5045 times)

Keith Broughton

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distributed speaker question
« on: January 16, 2015, 03:00:38 pm »

I am installing 6 speakers in a small office. The sound source is a home hifi integrated amplifier.
I could do a series/ parallel arrangement with the 8 ohm speakers, but the question is, can I use 25 volt transformers at the speakers to allow for individual levelling and drive them from the amplifier without a step up tansformer at the amp?
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Hal Bissinger/COMSYSTEC

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Re: distributed speaker question
« Reply #1 on: January 16, 2015, 03:53:42 pm »

Or 70 volt transformers. Sure, that's the way many amps derive a 25 or 70.7 volt output.

-Hal
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Lee Douglas

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Re: distributed speaker question
« Reply #2 on: January 16, 2015, 04:42:01 pm »

I am installing 6 speakers in a small office. The sound source is a home hifi integrated amplifier.

I would just get three impedance matching stereo volume controls and wire one to each pair of speakers in each office/location.  A Profficient VC45i volume control can be had for under $30 each.  Super easy.
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Keith Broughton

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Re: distributed speaker question
« Reply #3 on: January 16, 2015, 04:47:57 pm »

That's one solution that would work. I'll keep it in mind.

But...the question is...can I run a 25 volt distributed system directly from the output of the hifi amp without the use of a step up xfmr?
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Jason Lavoie

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Re: distributed speaker question
« Reply #4 on: January 16, 2015, 04:54:31 pm »

That's one solution that would work. I'll keep it in mind.

But...the question is...can I run a 25 volt distributed system directly from the output of the hifi amp without the use of a step up xfmr?

You can, but it'll be quiet. might be fine for an office situation.
Whether the amp will be happy depends on how you wire the transformers. if they're each tapped at 15W that gives a total impedance of 6.94ohms

Jason
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Mac Kerr

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Re: distributed speaker question
« Reply #5 on: January 16, 2015, 05:07:43 pm »

That's one solution that would work. I'll keep it in mind.

But...the question is...can I run a 25 volt distributed system directly from the output of the hifi amp without the use of a step up xfmr?

Sure, as long as the load impedance of the paralleled speakers doesn't fall below the rated low impedance spec of your amp. What horrible thing did you think might happen? Unless you have the proper amplifier the rated wattage taps of each speaker won't be accurate, but you won't damage anything by using a non-transformer output amp.

Mac

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John Roberts {JR}

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Re: distributed speaker question
« Reply #6 on: January 16, 2015, 05:44:20 pm »

I am installing 6 speakers in a small office. The sound source is a home hifi integrated amplifier.
I could do a series/ parallel arrangement with the 8 ohm speakers, but the question is, can I use 25 volt transformers at the speakers to allow for individual levelling and drive them from the amplifier without a step up tansformer at the amp?

How many watts is the amp? 25V is 78W @ 8 ohm so a 75w hifi amp would be reasonable to drive a 25V constant voltage network directly. While hifi amps may not be very robust.

JR
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Keith Broughton

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Re: distributed speaker question
« Reply #7 on: January 17, 2015, 06:40:45 am »

Thanks for all the responses. I now have the info I need. :)
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Ivan Beaver

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Re: distributed speaker question
« Reply #8 on: January 17, 2015, 09:18:43 am »

How many watts is the amp? 25V is 78W @ 8 ohm so a 75w hifi amp would be reasonable to drive a 25V constant voltage network directly. While hifi amps may not be very robust.

JR
That is a simple concept that many people don't understand.

Just like with a 70V system.  An amp that is rated for 600 watts @8 ohms will drive it without a transformer-and the low freq rolloff and saturation associated with it.

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Jason Lavoie

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Re: distributed speaker question
« Reply #9 on: January 19, 2015, 09:22:55 am »

An amp that is rated for capable of 600 watts @8 ohms will drive it without a transformer-and the low freq rolloff and saturation associated with it.
To be more specific :)
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Hal Bissinger/COMSYSTEC

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Re: distributed speaker question
« Reply #10 on: January 19, 2015, 04:28:02 pm »


Quote
An amp that is rated for capable of 600 watts @8 ohms will drive it without a transformer-and the low freq rolloff and saturation associated with it.
To be more specific :)

And right there is the difference between commercial and audiophile equipment. Only way to know what it is capable of is to put dummy loads on each channel and run it up to just before clipping. Then measure the voltage and do the math. While you are at it leave it cook for a few hours to see if it self destructs.  ;D Most audiophile equipment specs are wildly exaggerated.

-Hal
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Ivan Beaver

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Re: distributed speaker question
« Reply #11 on: January 19, 2015, 07:37:47 pm »

To be more specific :)


And right there is the difference between commercial and audiophile equipment. Only way to know what it is capable of is to put dummy loads on each channel and run it up to just before clipping. Then measure the voltage and do the math. While you are at it leave it cook for a few hours to see if it self destructs.  ;D Most audiophile equipment specs are wildly exaggerated.

-Hal
And I would argue that even pro or commercial amplifiers will not deliver full output-especially the large ones.

In many cases they can deliver the rated power for some very short period of time (often less than 1/10th of a second) and have a continuous output around 1/4 or less of the "peak" output.

And this goes for the most respected names in the business.
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Hal Bissinger/COMSYSTEC

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Re: distributed speaker question
« Reply #12 on: January 20, 2015, 01:34:14 pm »

And I would argue that even pro or commercial amplifiers will not deliver full output-especially the large ones.

In many cases they can deliver the rated power for some very short period of time (often less than 1/10th of a second) and have a continuous output around 1/4 or less of the "peak" output.

And this goes for the most respected names in the business.

I think a lot of that is to get around having to use Class 1 speaker wiring per UL and the NEC.

-Hal
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John Roberts {JR}

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Re: distributed speaker question
« Reply #13 on: January 20, 2015, 01:47:34 pm »

Wow now you guys are confusing me and I have actually designed install products.

Yes amps in general do not deliver full duty cycle. Haven't for several decades now. That said dedicated install products often encounter extremely compressed background music so actually experience higher duty cycle that live performance sound reinforcement.

It is common practice in constant voltage system design to budget in some amplifier power headroom (10% or more than needed). 

JR
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claude cascioli

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Re: distributed speaker question
« Reply #14 on: February 19, 2015, 08:51:23 pm »

I am installing 6 speakers in a small office. The sound source is a home hifi integrated amplifier.
I could do a series/ parallel arrangement with the 8 ohm speakers, but the question is, can I use 25 volt transformers at the speakers to allow for individual levelling and drive them from the amplifier without a step up tansformer at the amp?

yes you can a very good match
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Re: distributed speaker question
« Reply #14 on: February 19, 2015, 08:51:23 pm »


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