How do I run 1 amp into 2 cabs



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How do I run 1 amp into 2 cabs

Postby JTurbide » Tue Nov 27, 2018 7:38 pm

Yeah I know there's alot of info on the internet about it but I couldn't find an answer to my specific needs.

So, I want to run either my ampeg v2 (which can run at 8,4 or 2 ohms) or my Earth sound research which is solid state and rated at 2 ohms into both of my cabs.
One is a 1x15 Sunn rated at 8 ohms, the other is a Sound City 4x10 that is switchable between 16 and 4 ohms and have two jack input (so maybe four 4 ohms speakers ? IDK)
If possible I'd like to do it with two cables because that's all I have at the moment. So maybe head -> Sound City's first jack, and then from Sound city's second jack into the Sunn ?
Would that work ? What ohm should I run the amp ?

Also, both amps have two speaker output so maybe one of each into a cab ? would that work ? if so what ohm rating should the amp be at ?

Cheers
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Re: How do I run 1 amp into 2 cabs

Postby Benn Roe » Wed Nov 28, 2018 10:47 am

If you're runnng the cabs in series like that (one into the other, rather than both directly from outputs on the amp), all you have to do is add up the impedance of the individual cabs to get their total. The number you set the head for is the amp's minimum impedance, so make sure you set the amp to the highest number you can that is lower than or equal to the impedance of the cabs. The closer to the number, the better, but definitely don't let the speakers have lower impedance than what you have the amp set for.

In series, it sounds like the lowest you could get your speakers to would be 12 ohms. You could safely connect the V2 set at 8 ohms (or any setting, actually), but it's been my experience that the the greater the disparity between the amp's minimum impedance and the speakers' actual impedance, the less power you get out of the amp. It just feels less efficient or something. Mind you, I don't know shit about electronics, I just forced myself to know speaker connection math so I wouldn't blow anything up; I can only relay the math, not explain why it works that way.

Since your amps each have two speaker outputs, you also have the option of running the cabs in parallel, which has drastically different math. If cab 1's impedance is A, cab 2's impedance is B, and the total impedance is C, the forumla is (1/A)+(1/B)=(1/C). So, Sunn at 8 and Sound City at 4 would give you a total impedance of 2.666666 ohms, which is pretty close to the 2 ohm minimum of both amps. Two cabs at 4 ohms each would be exactly 2 ohms. For what it's worth, I've had several amp techs warn me against trusting any minimum rating of 2 ohms, because it's too close to 0, but lots of amps from the 70s claim to be able to go that low, so who knows? The main difficulty is that amps almost always have minimums of 2, 4, 8, or 16, and I don't think there's a way to hit any of those numbers on the nose with your mismatched speakers. You'd need two 4 ohm, or two 8 ohm, cabs to get the math to work out perfectly.
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Re: How do I run 1 amp into 2 cabs

Postby JTurbide » Wed Nov 28, 2018 11:09 am

Thanks ! So I could safely do both, at least to try it and see how it sounds. The fact that the cabs have different ohms won't damage anything ?
So can I do both with only 2 cables ?
So, to connect it in series I'd have to take one output of the amp, connect it to one of the input of the Sound City, and then from the other input (which would turn into an output) go to the sunn cab input ?
So head to first cab, first cab to second cab ?
In parallel it would be just each head output into a cab input right ?

I've seen some representative pictures online but it's not super clear to me.. according to google image parallel would actually be from one cab to another... :idk:

I'll probably get an aby at some point but apparently the passive ones are garbage and you need a $200 radial one... which is pretty expensive :grumpy:
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Re: How do I run 1 amp into 2 cabs

Postby Benn Roe » Wed Nov 28, 2018 1:36 pm

Can you link the Google image search you're seeing? I feel pretty confident about everything I told you, and it doesn't make any sense from a linguistic perspective that parallel would be from one cab to the other. You have it right, series would be from the amp to a cab, then from that cab to the other. Parallel would be each cab connected directly to separate outputs on the amp.

You can definitely safely do either method. Just make sure your total speaker impedance is never lower than the impedance your amp is set for. Either method would only require two cables, but make sure you're using speaker cables. I'm sure you know that, but I definitely used instrument cables before I knew better, so I'm mentioning it, just in case. They're not the same thing.
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Re: How do I run 1 amp into 2 cabs

Postby JTurbide » Wed Nov 28, 2018 3:04 pm

It makes absolutely no sense to me either. Thanks for the info!I'm seeing lots of threads (searching google) where people says it's not safe to run two cabs with different Ohms rating...


I think I'll continue to get as much info as I can before trying it.. I just want to make sure I don't damage anything,these are all rare and somewhat valuable pieces of gear...

Edit: called my tech, apparently it's safe but I need to know if the Sound city is wired in series or parallel..
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Re: How do I run 1 amp into 2 cabs

Postby Benn Roe » Wed Nov 28, 2018 8:43 pm

The Sound City is the one that switches between 4 and 16 ohms? I'd bet money that means it has four 4 ohm speakers, and switches between 1) the four speakers in series (4+4+4+4=16 ohms); and 2) two sets of two speakers each in series, but run together in parallel (((4+4=8)/1)+((4+4=8)/1)=(4 ohms/1)). There aren't a lot of other configurations that could result in 4 or 16. I guess they could be 16 ohm speakers running in 1) a parallel hierarchy for 4 ohms; or 2) in parallel then series for 16 ohms. Either way, it's not clear-cut series OR parallel; it would have to be a combination for one setting or the other. Your tech probably knows better than me, but I'm not really sure why it matters for your purposes. The resulting number is the resulting number; how it's wired internally shouldn't change the math at all.

There's definitely a lot of confusion about this out in internet-land, so I don't fault you for being careful. I feel pretty confident that my grip on this topic is firm, but I'm not a tech, so by all means seek other opinions.
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Re: How do I run 1 amp into 2 cabs

Postby JTurbide » Wed Nov 28, 2018 9:01 pm

I actually think it's 4 16 ohms speakers wired parallel (4 ohms) and series-parallel (16 ohms), but I might be wrong.
Also, I've done some research and apparently from one cab to another is actually in parallel, it doesn't makes sense to me but I think that's the way it is... both way we talked about is parallel... and series is some kind of other way you never see...
I also learned that with a solid state amp you can go above the ohm rating (ex: plug a 2 ohm head in a 4 ohm cab), but with tubes it's the other way. Tube amps are more sensitive to mismatch so you have to get as close as possible but if you have to mismatch you should go lower... I didn't know that.. at least that's what my amp guy told me and he's a well known tech here in Montreal and is a electrical engineer.

So yeah I'm currently waiting for is confirmation but a tried (cause I have zero patience in life) the Earth (cause if I'm gonna break one of the two I'd rather break the earth over the ampeg ;P ) into the sound city on 4 ohms, and the sound city into the sunn and it worked.. I didn't turn it all up or played for a long time but it worked for 2-3 minutes lol.
In the end it might be cool if I ever jam with this rig but in my appartment, the 4x10 overpowered the 1x15 (4 ohm vs 8ohm doesn't help) and I couldn't use my attenuator so...
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Re: How do I run 1 amp into 2 cabs

Postby Benn Roe » Thu Nov 29, 2018 1:07 am

Hmm. Interesting. I've never heard anything like that, but I always try to match exactly anyway.
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Re: How do I run 1 amp into 2 cabs

Postby comesect2.0 » Wed Dec 05, 2018 5:43 am

https://reverb.com/item/15152089-earcan ... ension-cab
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idk if this has anything to do with anything
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