Can you use 8 Ohm speakers with a 3 Ohm receiver? - AVS Forum
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post #1 of 13 Old 12-06-2008, 09:51 AM - Thread Starter
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I search for similar threads, but they seemed to deal with the reverse of what I was thinking of doing.

I picked up a cheap Sony HTS that supposed to be a 1000W receiver for my game room and then I noticed it's 3 ohm. I planned on upgrading the speakers on my main system and move some Def Tech PM 80s to that Sony system. I was wondering if the 8 ohm Def Techs will run on the Sony receiver and can it hurt them?

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post #2 of 13 Old 12-06-2008, 10:00 AM
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Quote:
Originally Posted by LowellG View Post

I search for similar threads, but they seemed to deal with the reverse of what I was thinking of doing.

I picked up a cheap Sony HTS that supposed to be a 1000W receiver for my game room and then I noticed it's 3 ohm. I planned on upgrading the speakers on my main system and move some Def Tech PM 80s to that Sony system. I was wondering if the 8 ohm Def Techs will run on the Sony receiver and can it hurt them?

Thanks

Not familiar with what model of Sony you're talking about, but I'll assume it's something that comes as a total HTIB type system.

Ratings of amps and AVRs can be wildly all over the map. There's just not one rating scale that you can glean to compare.

So, I'll make some generalizations here. The lower the impedance, the harder the load. Most amplifier sections will put out more watts and lower Ohms (as with most things, there are exceptions). That's not to say that they do so cleanly, at an acceptable THD level (generally .1% or lower is acceptable) or with acceptable sound. But, to hit a spec, that's what they're quoting (1000 watts). If you divide that up into 5 channels, that means it's putting out 200 watts per channel, but who knows if it's simultaneously, or with acceptable THD.

I know of no Sony product, even their ES stuff, that's capable of doing that within acceptable parameters.

My guess is the Sony can indeed drive your 8 Ohm Def Techs. What it sounds like in doing so is another matter entirely.

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post #3 of 13 Old 12-06-2008, 10:03 AM
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Some boxed systems seem to be optimized for the speakers hooked up to them. Running it with other speakers than it was designed for may not work as well. You can always try it. 8 ohm loads are not particularly difficult.

"But this one goes up to 11"
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post #4 of 13 Old 12-06-2008, 11:37 AM
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If that Sony is a HTIB type receiver you risk damaging your speakers with it, because it will not provide enough current at higher volumes to prevent clipping. The power specs on that receiver are highly misleading and are probably based on very short dynamic power to one channel at low impedance (3 ohms) at 1KHz and 1.0 THD, while the better standard is continuous output in 2 or more channels at 8 ohms, 20Hz-20KHz, with THD less than .05. Here is a readable article that will help you understand better:

http://hometheatermag.com/advicefrom...507powerspecs/

And here is a whole list of articles that will provide more reading if you like:

http://www.ecoustics.com/Home/Home_A...iver_Articles/

And here (amplifiers):

http://www.ecoustics.com/Home/Home_A...fier_Articles/

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post #5 of 13 Old 12-06-2008, 03:21 PM - Thread Starter
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I forgot to mention, I have this one.

http://www.sonystyle.com/webapp/wcs/...52921665368399

Lowell


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post #6 of 13 Old 12-06-2008, 05:14 PM
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Audio Power Output : 1000W (143w x 5 + 285w (1KHz, 10% THD))
Impedance : 3 ohms

I would leave it as a packaged system. If you want to upgrade, get better speaker and a better receiver to go with it.

 

 

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post #7 of 13 Old 12-06-2008, 06:59 PM - Thread Starter
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Thanks for the advice. I think I will just move my Onkyo 605 in when I upgrade.

Lowell


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post #8 of 13 Old 12-06-2008, 08:19 PM
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Quote:
Originally Posted by dsmith901 View Post

If that Sony is a HTIB type receiver you risk damaging your speakers with it, because it will not provide enough current at higher volumes to prevent clipping. The power specs on that receiver are highly misleading and are probably based on very short dynamic power to one channel at low impedance (3 ohms) at 1KHz and 1.0 THD, while the better standard is continuous output in 2 or more channels at 8 ohms, 20Hz-20KHz, with THD less than .05. Here is a readable article that will help you understand better:

http://hometheatermag.com/advicefrom...507powerspecs/

And here is a whole list of articles that will provide more reading if you like:

http://www.ecoustics.com/Home/Home_A...iver_Articles/

And here (amplifiers):

http://www.ecoustics.com/Home/Home_A...fier_Articles/

Completely wrong. Look up previous posts on the subject on this forum by Bob Lee. Stop spreading the FUD.

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post #9 of 13 Old 12-06-2008, 10:14 PM
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Quote:
Originally Posted by LowellG View Post

I forgot to mention, I have this one.

http://www.sonystyle.com/webapp/wcs/...52921665368399

In the immortal words of 'Crocodile Dundee'

You call that a knife?













































http://www.emotiva.com/xpa5.shtm

Now that's a knife.
Wow, there really should be some better measuring stick for all amplifiers to abide by.
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post #10 of 13 Old 12-06-2008, 10:48 PM
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Quote:
Originally Posted by DonoMan View Post

Completely wrong. Look up previous posts on the subject on this forum by Bob Lee. Stop spreading the FUD.

Next time simply share your knowledge opposed to touting someone else's name on the forum based off their knowledge on a particular subject. What's the point of replying to a post to simply go, "NOPE YOU WRONG BECAUSE SOMEONE ELSE SAID SO!"

I'm assuming you are referring to this post?

Quote:
Originally Posted by Bob Lee (QSC) View Post

Clipping is not dangerous to loudspeakers in itself; the main danger to loudspeakers that it poses is that of excessive power. When an amplifier clips, it is putting out power in excess of its rating. Extremely severe clipping that produces an actual square wave will result in up to twice as much power as a clean sine wave at the threshold of clipping would produce (in reality, though, that much clipping would be extremely difficult to produce without a circuit malfunction, and the power supply rail voltages would tend to sag under such heavy demand).

Thus, a 100-watt amp could damage a loudspeaker rated for 150 watts continuous power if it is allowed to clip heavily, even though the ratings of both might lead one to conclude that the combination couldn't possibly be anything other than completely benign. That same amp, though, would not be likely to damage a loudspeaker that is capable of, say, 250 or 300 watts of continuous power, even if it is driven to severe clipping.

It is my understand clipping will be reached sooner with an underpowered receiver, however, average power at too high a level (without clipping even) is usually the cause of thermal/mechanical faulure.
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post #11 of 13 Old 12-06-2008, 10:59 PM
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Driver damage from clipping is often carelessly explained. Bob's explanation and Rodd Eliott's explanation at sound.westhost.com agree perfectly.

But he's not saying that amplifiers rated for more power than a speaker's continuous rating are inherently bad. What he's saying is that power, in general, kills drivers, usually due to thermal overload.

Tweeters, in particular can't handle a lot of power. See Rod Elliott's explanation of why tweeters blow. But let's say you are pushing 80 watts of non clipped power into a speaker rated at 50 watts continuous. Based on what I have read, this may be dangerous than clipping, for exactly the reason Bob explains.

There are two causes of speaker damage
* Thermal overload ( By all accounts, something that can happen with clipping)
* Mechanical overload ( I can exceed the woofer excursion limits on my small ACI Sapphires, and only a deaf person would not hear that)

You don't want to exceed either limit no matter how weak or powerful your receiver/amp is.

The bottom line is to not operate your speakers when you can hear any obvious distress. Besides, if you run your speakers at too high of a volume they will sound bad. Turn it up until the sound quality drops, then back down a bit. This should work whether your amp has too little power, or too much power.

"But this one goes up to 11"
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post #12 of 13 Old 12-07-2008, 08:01 AM
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Quote:
Originally Posted by gunbunnysoulja View Post

Next time simply share your knowledge opposed to touting someone else's name on the forum based off their knowledge on a particular subject. What's the point of replying to a post to simply go, "NOPE YOU WRONG BECAUSE SOMEONE ELSE SAID SO!"

Because I love to reinvent the wheel every time someone mistakenly quotes the "OMG CLIPPING KILLS YOUR SPEAKERS" FUD.

That would be far too often. I guess I should keep Bob's quotes on my clipboard at all times.

"Vintage" is good for wine, not for A/V equipment.

-Dan D.
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post #13 of 13 Old 12-07-2008, 09:42 AM
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Clipping can kill your speakers, trust me It's the specifics of WHY it kills your speakers that's not always fully understood.

"But this one goes up to 11"
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