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  #1  
Old 06-13-2011, 07:17 PM
70WR 70WR is offline
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What happens running 4 ohm amp connects to 8 ohm speakers?

What happens - short/long term?

I just found out that on one of my amps, the 4 ohm speaker connects (banana plugs) I had feeding 8 ohm speakers - been this way less than 2 weeks.

I found how to do it, both 4 into 8 and 8 into 4, but I don't want to know how to do it - just what happens when its done.

How I did it - I was running my tube amp into 4 ohm Maggie's, then over a week ago I pulled the banana plugs from the Maggie's (MG-I) and just plugged them into 8 ohm speakers, not thinking the other end of the wires were fed from the tube amp 4 ohm speaker connects instead of the 8 ohm speaker connects.


So to add to to my wondering, what if it was the other way around, amp 8 ohm fed to 4 ohm speakers.
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Old 06-13-2011, 07:21 PM
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icenine icenine is offline
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No problem running 8 ohms on a 4 ohm tap....you just do not want to do the reverse i.e. run a 4 ohm speaker on an 8 ohm tap....
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Last edited by icenine; 06-14-2011 at 12:07 PM.
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Old 06-13-2011, 07:53 PM
70WR 70WR is offline
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^ Whew! I didn't know of harm to the speakers and/or amp. For over a week, I ran it like this daily from 2 to 8+ hours. I didn't push the amp hard so I figured maybe I'll be alright.

So if amp at 4 ohms to 8 ohm speakers is okay - why not leave the speakers wires connected to the 4 ohm connects on the amp all the time - then when I swap speakers between 4 ohm and 8 ohm - nah, scratch that - I learned a lesson and hope to always make it a point on checking this whenever switching speakers/amps etc.

I figured running amp (8 ohm) to speakers (4 ohm) is worse than what I had done. Impedance mismatch would be worse.

Thanks
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Old 06-13-2011, 08:03 PM
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icenine icenine is offline
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Best bet is too know what load your amp can run.....read the manual. And be careful running four speakers (A+B outputs) at same time.....playing four 8 ohm speakers creates a 4 ohm load to the amp. Playing four 16 ohm speakers at the same time would make an 8 ohm load, which would be safer for most amps but there are not a lot of 16 ohm speakers out there. I know it gets confusing.
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Old 06-13-2011, 08:16 PM
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shelly_d shelly_d is offline
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4 ohm output into 8 ohm speakers = less power output and perhaps less distortion. This can be a good thing if you end up not being shy on power, that is not pushing the amp all the way into clipping.

Reversing the mismatch and you could get excessive heat build up in the amp's output and may increase distortion, neither is a good thing.

Shelly_D
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Old 06-13-2011, 10:11 PM
donberry donberry is offline
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actually, many will recommend trying it out on both and see if there is a difference in sound and use the one you prefer. For tube amps anyway.
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Old 06-13-2011, 10:31 PM
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MelodyMaster MelodyMaster is offline
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Quote:
Originally Posted by donberry View Post
actually, many will recommend trying it out on both and see if there is a difference in sound and use the one you prefer. For tube amps anyway.
I run 8 ohm speakers on the 4 ohm tap anyway because I never approach full output and it does sound a bit sweeter that way, smoother bass and highs.
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Old 06-13-2011, 11:45 PM
70WR 70WR is offline
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I didn't know there were recommendations for this - and here I nearly had a stroke the moment I saw it, a panic shut down - for no legit reason I guess other then I thought at the moment "what am I doing to my amp!" - all for nothing

Thanks again all - maybe I'll do a comparison, I actually didn't notice it but wasn't doing it looking for a change.
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Old 06-14-2011, 05:20 AM
gushtone gushtone is offline
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Quote:
Originally Posted by donberry View Post
actually, many will recommend trying it out on both and see if there is a difference in sound and use the one you prefer. For tube amps anyway.
On a related note, I run my old Marshall head at 8 ohms into a 16 ohm 4x12 cab and I always preferred the sound to the 16=>16. Let's me push it a bit harder and sounds warmer.

Peace...
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Old 06-14-2011, 11:57 AM
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mhedges mhedges is offline
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You will lose some potential power by running 8 ohm speakers on a 4 ohm tap but other than that nothing will be hurt.
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  #11  
Old 06-17-2011, 01:57 PM
BADBOB BADBOB is offline
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Hello . Newbie here so please forgive me for not knowing the rules yet.
This is a new thread about bi-amping .
I have a pair of infinity kappa 8.1 . I have a pair of mcintosh mc2500 amps. How do i hook these up and what do i need to hook these up ?
Any info would be appreciated .
Thanks
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  #12  
Old 06-17-2011, 05:25 PM
positron positron is offline
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Quote:
Originally Posted by shelly_d View Post
4 ohm output into 8 ohm speakers = less power output and perhaps less distortion. This can be a good thing if you end up not being shy on power, that is not pushing the amp all the way into clipping.

Reversing the mismatch and you could get excessive heat build up in the amp's output and may increase distortion, neither is a good thing.

Shelly_D
Nice points Shelly. To add a little more, running 8 ohm speakers on 4 ohm amp output will reduce peak plate currents. This is helpful when running class AB and B as plate dissipation is reduced. However, as Shelly mentions, output power is usually reduced a little as well. Damping factor is increased with such a setup compared to 8 ohm speakers on 8 ohm tap.

As Shelly also points out, reverse mismatch will cause excessive peak plate current, increasing plate dissipation, which is not good for the output tubes.
Damping factor is also reduced.

Cheers.
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Old 02-05-2013, 08:57 AM
rucyrius rucyrius is offline
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Parallel

If the two 8 ohm speakers are wired in parallel and tapped into 4 ohm on the amp isn't that cutting the speakers to 4 ohm and it's all running at 4 ohms?

Also what happens if you have two sets of 8 ohm speakers running from a 4 ohm tap running at the same time ... I have a fisher 500c set on 4 ohms.. To a speaker switcher .. Most of the speakers are 8 ohm. ( one set in living room are 4 ohm super sensitive(95)) there are 4 sets of speakers in all ... I never run them all at the same time .. But am I asking for trouble if I have two sets on at a time... And what if I run one set of the 8 ohm speakers at the same time as the 4 ohm set ... They sound ok when I do it but I'm worried I'll blow up the vintage amp... Thoughts?
Thanks
John
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  #14  
Old 02-05-2013, 10:40 AM
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shelly_d shelly_d is offline
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Quote:
Originally Posted by rucyrius View Post
If the two 8 ohm speakers are wired in parallel and tapped into 4 ohm on the amp isn't that cutting the speakers to 4 ohm and it's all running at 4 ohms?

Also what happens if you have two sets of 8 ohm speakers running from a 4 ohm tap running at the same time ... I have a fisher 500c set on 4 ohms.. To a speaker switcher .. Most of the speakers are 8 ohm. ( one set in living room are 4 ohm super sensitive(95)) there are 4 sets of speakers in all ... I never run them all at the same time .. But am I asking for trouble if I have two sets on at a time... And what if I run one set of the 8 ohm speakers at the same time as the 4 ohm set ... They sound ok when I do it but I'm worried I'll blow up the vintage amp... Thoughts?
Thanks
John
2 sets of 8 ohm speakers in parallel are 4 ohms to the amp. Period. Treat them the same as a 4 ohm set of speakers.

4 Ohm speakers in parallel with 8 ohm speakers makes the amp see 2.6 ohms. Place such a pair on any 2 ohm tap you may have. If you don't have a tap that goes down to 2 ohms, you should not run them in parallel. In my opinion it is just too low for the amp and could cause heat related issues in the long run, even if not causing issues in the short run.

Shelly_D
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  #15  
Old 02-05-2013, 11:38 AM
rucyrius rucyrius is offline
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Quote:
Originally Posted by shelly_d View Post
2 sets of 8 ohm speakers in parallel are 4 ohms to the amp. Period. Treat them the same as a 4 ohm set of speakers.

4 Ohm speakers in parallel with 8 ohm speakers makes the amp see 2.6 ohms. Place such a pair on any 2 ohm tap you may have. If you don't have a tap that goes down to 2 ohms, you should not run them in parallel. In my opinion it is just too low for the amp and could cause heat related issues in the long run, even if not causing issues in the short run.

Shelly_D
Then if I run the 4 Ohm speakers along with the other two sets of 8 ohm speakers .. What does that do to the amp?

Otherwise I should make sure the 4 ohm speakers are only run by themselves. Ie: without other 8 ohm speakers switched on?
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