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Running 8ohm speakers on a 4ohm amp


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#1 shizzle

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Posted 12 April 2010 - 04:59 PM

Heya,

After seeing mosoto's for sale advert this morning, I realised my PG Xenon 200.4 is not 8ohm stable in normal stereo mode. I misread the bridged 8ohm rating, and thought it was for stereo too.

Now, I have some USD Waveguides (8ohm) running off 2 channels on the amp, they have been running for a few months now, and to me, sound fine, with plenty of volume.
My question is, will the amp get damaged over time, running at 8ohm's, when it is only rated at 4?

The amp has not been getting hot, and as mentioned, sounds fine. I realise I will not be getting the 200W rated for the channel, probably less than half of that. The guides are only rated at 65w though, with good efficiency, so that is not a huge deal.

Any help is appreciated, as I do not want to kill my amp, but on the same side, do not want to spend more money on another amp if it is ok to run it like that.

Thanks,

#2 2LOUD2OLD

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Posted 12 April 2010 - 05:04 PM

it'll be fine there is no problem running amps at a higher impendence, it is when you try to run them lower that you have a problem

#3 Tiger

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Posted 12 April 2010 - 05:33 PM

I'm running Dayton RS52 mids (60WRMS 8ohm) MOST likely off a bridged F407 Alpine amp (about 120WRMS at 4ohm bridged). So that'll be fine :)

And dont forget, horns need bugger-all power to make them sing. You would'nt want anything above 50WRMS going into your Waveguides anyway otherwise you'd rip your head off with them! I had a pair of Waveguides myself. They were only going to see 50WRMS on 4ohm

#4 ~Spyne~

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Posted 12 April 2010 - 05:54 PM

it'll be fine there is no problem running amps at a higher impendence, it is when you try to run them lower that you can have a problem


this

#5 shizzle

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Posted 12 April 2010 - 06:39 PM

cool, thansk guys. Always good to get confirmation, before one lets out the magic smoke from the caps :)

#6 Gonadman2

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Posted 12 April 2010 - 06:43 PM

Rated impedance is usually the minimum impedance of the driver with respect to frequency. Most of the played frequency range of a driver is a higher impedance than its rater impedance.

#7 Big_Valven

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Posted 12 April 2010 - 07:24 PM

Exactly Gonads, I was about to mention Impedance is a nominal minimum value. Impedance higher than minimum ratings are all good :)

#8 Tiger

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Posted 12 April 2010 - 07:57 PM

So are you saying that me running 2 set of 4ohm speakers down to 2ohm stereo wouldn't be a good thing? Because I'm looking at running my midbass drivers at 2ohm stereo

#9 Big_Valven

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Posted 12 April 2010 - 08:22 PM

You need an amplifier that is 2 ohm stable then Tiger :)

#10 Tiger

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Posted 12 April 2010 - 08:29 PM

Like an Alpine MRV-1507? ;)

#11 Big_Valven

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Posted 12 April 2010 - 08:38 PM

I knew you had it figured out already. :)

#12 Gonadman2

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Posted 12 April 2010 - 09:39 PM

So are you saying that me running 2 set of 4ohm speakers down to 2ohm stereo wouldn't be a good thing? Because I'm looking at running my midbass drivers at 2ohm stereo

Well, if they were midrange speakers and the minimum nominal impedance was 4ohms at 100Hz but rose to 6ohms at 400hz you 'might' get away with a crossover at 400-500hz. But why would you?

#13 Tiger

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Posted 12 April 2010 - 09:58 PM

Have a look in my signature at the bottom. You'll see the Exodus Audio Anarchy mids I wanna run at 2ohm stereo.

#14 mosoto

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Posted 12 April 2010 - 11:18 PM

but doesn't lowering the impedance below it's rated value degrade the quality of the sound?

Edited by mosoto, 12 April 2010 - 11:19 PM.


#15 Tiger

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Posted 12 April 2010 - 11:36 PM

I'm assuming it doesn't. If it does, someone will have to document why it's so.

#16 KGB

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Posted 13 April 2010 - 08:54 AM

There is something about the damping factor and the amp controlling the speaker at lower impendences, someone like Muzzy or TheMatt will be able to explain it. Whether it makes a difference in a car and whether we'd be able to tell is another story.

#17 Big_Valven

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Posted 13 April 2010 - 10:36 AM

It takes a big a/b compared drop, but it is possible to tell the difference in some cases. The amplifier has less damping over unwanted speaker movement at lower impedances (movement of the speaker that doesn't correspond to the original signal.)

I wouldn't use a speaker setup below minimum nominal impedance on an amplifier unless I was being silly, or wanting to do SPL stuff.
The fact that most speakers rise above minimum nominal impedance most of the time doesn't mean you can really get away with lower than rated impedances - the amplifiers are rated with this in mind.
I'm sure we all know that amplifiers work plenty hard even above minimum impedance, running below it is just tempting fate.

Edited by Big_Valven, 13 April 2010 - 10:36 AM.