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Matching speaker impedance

sheepshagger
Dabbler
Posts: 15
Registered: 09-01-2008

Matching speaker impedance

Can anyone confirm something for me. I am replacing a tv with built in dolby digital amplification. I am looking for an amplifier and I'm not too sure about matching impedances. My front and rear speakers are 4-8 ohm. My centre speaker is 8 ohm. So far so good. An amp rated 8 ohm will do the job. But. My sub is a passive. It has connections in at 8 ohm and connection out to satellites  at 4-8 ohm. Am I right in assuming that an 8 ohm amp will be ok with the sub albeit with a reduced output due to the doubled? impedance
7 REPLIES
Community Veteran
Posts: 7,149
Thanks: 51
Fixes: 2
Registered: 30-08-2007

Re: Matching speaker impedance

I would guess you will have no trouble with what you propose. However, if in doubt you should be able to purchase a speaker matching transformer which will solve the problem as long as you are handy with a soldering iron. But most of the speaker mismatch issues I came across were mostly with valve amps, where they could run very hot, but with "solid state" amps I never experienced much of a problem. You would need a very discerning ear indeed to hear the difference at "normal" volume levels, at very low volume it may be an issue for you.
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sheepshagger
Dabbler
Posts: 15
Registered: 09-01-2008

Re: Matching speaker impedance

Thanks for that. I thought it would be ok especially as the amp output is significantly more than the speakers could take. Just one thing. I was also looking at a 6 ohm impedance amp. i presume the 8 ohm amp would be better in the circumstances
alanb
Grafter
Posts: 459
Registered: 24-05-2007

Re: Matching speaker impedance

As a general principle, if the amp and speaker impendences can't be matched, it's best to have speakers with impedences that are higher than the amp. If the speaker impedences are lower, then more current fows through the speaker coils, introducing a slight risk of damage to either amp or speakers if the amp cannot cope, (though it shouldn't be a problem in practice, unless you like to crank the volume up to 11 all the time).
sheepshagger
Dabbler
Posts: 15
Registered: 09-01-2008

Re: Matching speaker impedance

Thanks. So really I could buy either amp and there isn't much difference in suitabilty between them
alanb
Grafter
Posts: 459
Registered: 24-05-2007

Re: Matching speaker impedance

I've not come across an amp with 6 Ohm speaker outputs before. I assume the manufacturer views it as a convenient way of supporting either 4 or 8 Ohm speakers without going to the expense of adding separate output stages to match both speaker types. You could try quizzing the retailer on that if they're likely to know what they're talking about.
If you're sure that the sub-woofer is 8 Ohm (I'm hedging because I'm unsure why you think the impedance will be doubled, and you also give the impression that the front and back speakers have seperate amplification) then either amp should do the job.
Personally though, I think I'd avoid the 6 Ohm one, not because I think it would not work, but simply because if I could get a correctly specified amp, it'll be one less thing that could get in the way of a successful warranty claim, if any of the kit ever needs to be returned under warranty for any reason.
sheepshagger
Dabbler
Posts: 15
Registered: 09-01-2008

Re: Matching speaker impedance

The sub is 8ohms from amplifier and 4-8ohms to satellites.  The 6ohm amp is a kenwood. The other (8ohm) is a sony. Both front and rear are4-8ohm and the centre is 8 ohm. I think I'll go with the Sony. Thanks
Community Veteran
Posts: 3,364
Thanks: 15
Registered: 06-04-2007

Re: Matching speaker impedance


I'd not worry too much, due to manufacturing variances is speaker transducers, it easy to get a 1 or 2 ohm difference from units coming of the same production line! Only in high end speakers will they select on test from the production line those transducers with the similar performance.
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