Different cabs at different ohms

Michael6120

Member
Messages
437
Hi guys, been doing some bigger gigs with 2 quads however they're different brands but both 16ohm. I run the amp at 8ohm and come out from the 2 outputs on my head.

I just found a crazy cheap quad for sale to match one of my current ones.. however the one for sale is 8ohm... so I'd have to play with one cab being 16 and the other being 8.

It isn't going to work is it? I mean regarding running the rig safely considering the amps transformer..
 

cardinal

Member
Messages
5,189
I'd definitely be a mismatch. How safe depends on the amp, etc. Mesa, for example, says it's safe with some other their amps. One of the cabs might end up louder than the other, but I get confused on the technical aspects.

You could buy the new cab , swap speakers and then sell the older cab with the 8 ohm quad.
 

Michael6120

Member
Messages
437
I'd definitely be a mismatch. How safe depends on the amp, etc. Mesa, for example, says it's safe with some other their amps. One of the cabs might end up louder than the other, but I get confused on the technical aspects.

You could buy the new cab , swap speakers and then sell the older cab with the 8 ohm quad.
Ah yeah, that's definitely an idea (swap what I need, sell what I need)
 

ironman28

Gold Supporting Member
Messages
590
Ahh that's a shame. Thanks
If your amp has 4/8/16 ohm outputs you can run the 8 ohm cab on the 4 ohm tap and the 16 ohm cab on the 8 ohm tap.
This will result in equal power to each cab and a matched load to the amp. If your amp has an impedance selector you cant do this.
 

Michael6120

Member
Messages
437
If your amp has 4/8/16 ohm outputs you can run the 8 ohm cab on the 4 ohm tap and the 16 ohm cab on the 8 ohm tap.
This will result in equal power to each cab and a matched load to the amp. If your amp has an impedance selector you cant do this.
Thanks for that info. No I've got an old school marshall...

Shame as I could of had a sweet looking rig this weekend.
 

woof*

Member
Messages
7,859
Just swap speakers so both are 16, don't run a 100 watt marshall with two different ohm cabs....in the old days we blew transformers this way.
 

GCDEF

Silver Supporting Member
Messages
27,892
Just swap speakers so both are 16, don't run a 100 watt marshall with two different ohm cabs....in the old days we blew transformers this way.
As long as you set the amp to 4 ohms, nothing would blow. As mentioned though, the 8 ohm cabinet would get twice as much power.
 

Silent Sound

Member
Messages
5,115
RTotal = R1+ R2+ R3+....

or

I've got no idea what's happening
That's because he gave you formulas for calculating resistance in series and parallel (respectively). What you need is the formula for calculating impedance since we're dealing with an AC signal, of course. Lucky for you, this conversion is a simple one. On these particular formulas, you may assume Z=R and proceed. However, be warned that Z will not always equal R in all formulas.
 

IM4Tone

Member
Messages
3,770
Just swap speakers so both are 16, don't run a 100 watt marshall with two different ohm cabs....in the old days we blew transformers this way.
Yep. Buy the cab you're looking at and swap its speakers with the quad you own that doesn't match. Then sell that quad if you have no use for an 8 ohm quad.
 




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