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Author: Subject: Two sets of speakers with different impendance

Maximum Peach





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  posted on 6/25/2015 at 11:01 PM
In all these years of changing out stereo equipment I've never paid any attention to amp ohm ratings and speaker ohm specs.

I got a new simple Onkyo TX8050 stereo receiver/amp for some basic audio use in our living room. The speakers in question are small bookshelf types that currently are 4 ohm wired on the "A" set and some outside speakers that are 8 ohm on the "B" set.

I'm not sure I can safely run these both with set "A" and set "B" on together? I mean, I can, I did...but not sure it is good for the amp?

Onkyo book tells me I can use a 4 ohm speaker when running ONE speaker pair (A OR B) and I can set the receiver impedance to 4 ohm (which I did - the default was 6) and it clicked when I changed it.

The Onkyo book also says that when using both "A" AND "B" together use impedance 8 to 16 speakers and set the amp menu setting to 4 ohm.

But mine are 4 - 8 impedance and the book doesn't give a suggested setting for that.

If I'm running those 4 and 8 speakers together should I set the receiver to 4 or 6 you think? I'm sure it has something to do with amps produced (and in turn heat), as well as loudness of the speakers...not sure if any damage would be done either way?

Thanks for any input.

 
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A Peach Supreme



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  posted on 6/26/2015 at 01:15 AM
Thank YOU for the output....




 

True Peach



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  posted on 6/26/2015 at 07:14 AM
http://www.sengpielaudio.com/calculator-AmplifierLoudspeakerAndOhm.htm

 

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  posted on 6/26/2015 at 08:01 AM
quote:
http://www.sengpielaudio.com/calculator-AmplifierLoudspeakerAndOhm.ht m



Thanks for clearing that up

This makes it very clear:

DF = Zin / Zout = VL / (V0 ? VL)


Edit: I am just kidding, I should stay out of this conversation, have been baffled by some of this for quite some time in my life.

[Edited on 6/26/2015 by heineken515]

 

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  posted on 6/26/2015 at 08:38 AM
I was going to post the same website as the poster above.

Most amplifiers that allow 2 speakers to be connected will simply connect them in parallel.

So what you have is a 4 ohm speaker in parallel with an 8 ohm speaker. This presents a nominal load to the amplifier of 2.67 ohms. If you had two sets of 8 ohm speakers the impedance seen by your amp would be 4 ohms which is why they recommend 8-16 ohm speakers for 4 ohm setting.

http://www.sengpielaudio.com/calculator-paralresist.htm

The lower the impedance forces the amplifier to source more output current to drive the speaker as current = Voltage / resistance (impedance).

While it most likely won't hurt your amplifier some amps do not like driving low impedance loads as they cannot handle sourcing the current required and at high volume there is some risk of damaging the output stage (transistors).

JMO but I would check to see how hot the enclosure of your amp gets with the 4/ 8 ohm speaker combo and if it seemed to be running hot to the touch at high volume you may want to discontinue that combo of speakers or just don't crank the volume too high.

Hope this helps


http://www.gcaudio.com/resources/howtos/spkramp.html

http://www.hometoys.com/content.php?url=/htinews/feb04/articles/polk/impede nce.htm


 

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  posted on 6/26/2015 at 10:11 AM
Ideally you don't want to run speakers that don't have the same ohm setting....if you hook the the 2 4ohm together and then the 2 8ohm together it will be a very unbalanced load on the amp. And you can't run the 4ohm with the 8ohm in line because of the mismatch

 

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Maximum Peach



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  posted on 6/29/2015 at 08:31 AM
Thanks guys.

Let me do some reading on the links. I googled a couple things first, but was getting confused so I thought I'd come to my "source" for all things music.


 

Extreme Peach



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  posted on 6/29/2015 at 08:59 AM
quote:
Ideally you don't want to run speakers that don't have the same ohm setting....if you hook the the 2 4ohm together and then the 2 8ohm together it will be a very unbalanced load on the amp. And you can't run the 4ohm with the 8ohm in line because of the mismatch


Running speakers with different nominal impedances is not an imbalance but can present the amp with a low nominal impedance that may over drive the amp. There are amps out there that are designed to drive very low impedances but they are usually the high end expensive amps.

If the speakers are connected properly, an 8 ohm and 4 ohm speaker connected to the left and right channels then there is no imbalance since the amplifier will only see it as an impedance.

As long as the left and right channels see the same impedance then there is no imbalance.

The only way the amp would see it as an imbalance is if he hooked both 4 ohm speakers to the right channel terminals and both 8 ohm speakers to the left channel terminals or vice a versa. In that case the right channel would see a nominal impedance of 2 ohms while the left channel would see 4 ohms. That would be an imbalance which would not be good for the amp.

If he hooks up the 4/8 ohm speakers properly the amp will then see a nominal impedance of 2.67 ohms which at high volume playing could result in trying to draw too much current from the output stage which can damage the output transistors

 

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  posted on 6/29/2015 at 06:25 PM
If it is an issue you can always buy one of these''

http://www.russound.com/speakerselector_overview.php

 

Peach Pro



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  posted on 6/29/2015 at 09:08 PM
Running an Onkyo amp with a 2.67 ohm load is not ideal, but if you don't play them loud, you'll be OK. Just check on the temp of the amp when you've got them cranked up, if it gets hot, you're putting the hurt on it. Onkyo amps have built in thermal protection which will shut it down if you push them too much.

A friend had a big 160 watt, 11.2 channel amp that we ran into thermal protection by bi amping a pair of 4 ohm speakers (2 ohm load) and a Gov't Mule boot leg (Carbondale 1999)!

 

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  posted on 6/29/2015 at 09:40 PM
- I have an Onkyo receiver which I run up to 4 sets of speakers through a Russound as well as a separate power amp which runs my rock speakers. Both of them have a great safety cut off so you probably will have them cut off on you before they do any damage
 
 


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