2x12 mesa cabs / Help with impedance

Hey all,

I'm new to all this speaker impedance stuff. I have a dual rec and two 2x12 mesa cabs. Do i run 1 cab in the 8ohm slot and use the parallel jack on the back of the cab to connect the second? Or should i just plug both into the two 4 ohm jacks on the back of the amp? Or does it matter? Thanks for all your help.

If you have two 2x12 Mesa cabs, I assume they are both 8 ohms (which is standard for Mesa), to use both cabs at 8 ohms each, the jacks on the back of the amp are meant to represent total impedance applied to the jack. The proper hookup for two 8 ohm cabs is to connect each into the two 4 ohm jacks as their parallel impedance will be 4 ohms.

If you use the in/out jack on the speaker cabinet instead to link the two cabs together, you must use the 4 ohm jack on the amp to power them.

Total load the amp will see can be calculated by simple math. Load = (imp cab 1 x imp cab 2) / (imp cab 1 + imp cab 2).
Example: total load of two 8 ohm cabs is = (8x8)/(8+8) = 64/16 = 4 Connect both cabs to the two 4 ohm jacks or one cable to the 4 ohm jack and use a cable on the out to the in on the other cab.

There is a reason why there are two 8 ohm jacks and two 4 ohm jacks. Say you have two Marshall cabs or other brand that are both 16 ohms each, If you do the math (16x16)/(16+16) that would be 256/32 = 8 So the two 16 ohm cabs would both use the 8 ohm jacks.
Mesa runs an 8 ohm as their standard impedance so if you have two cabs, use the two 4 ohm jacks, if you only have one cab, use the 8 ohm jack.
I hope that makes sense.

Understood. Thanks Bandit! So, i also have a PRS MT100. The speaker outs on the back are 1 x 16 ohm. Then, in a box that says, "Jacks wired in Parallel" 1 x 8 ohm and 2 x 16 ohm.

I guess there isn't a way to use 2 Mesa 2x12 8 ohm cabs in parallel with this amp? Thanks for all your help.

Dyerwolf4 said:

Understood. Thanks Bandit! So, i also have a PRS MT100. The speaker outs on the back are 1 x 16 ohm. Then, in a box that says, "Jacks wired in Parallel" 1 x 8 ohm and 2 x 16 ohm.

I guess there isn't a way to use 2 Mesa 2x12 8 ohm cabs in parallel with this amp? Thanks for all your help.

Click to expand...

You'd have to wire the cabs in series to make them a total of 16 ohms. Four 16 ohm speakers can be either 4 ohms or 16 ohms (or 64), but never 8.
Two 8 ohm cabs in parallel, whether one cab plugged into the other, or both plugged into the amp, go in the 4 ohm output(s).
Check the amp manuals for possible "safe mismatches" listed. The Mark V allows a 16 ohm cab on the 8 ohm tap or an 8 ohm cab on the 4 ohm tap, or both simultaneously. But ONLY do this is your specific amp's manual states it's a "safe mismatch".

DECEMBER said:

You'd have to wire the cabs in series to make them a total of 16 ohms. Four 16 ohm speakers can be either 4 ohms or 16 ohms (or 64), but never 8.
Two 8 ohm cabs in parallel, whether one cab plugged into the other, or both plugged into the amp, go in the 4 ohm output(s).
Check the amp manuals for possible "safe mismatches" listed. The Mark V allows a 16 ohm cab on the 8 ohm tap or an 8 ohm cab on the 4 ohm tap, or both simultaneously. But ONLY do this is your specific amp's manual states it's a "safe mismatch".

Click to expand...

Yeah, these are stock boogie 2x12s so i'm not going to mess with trying to rewire anything. So for the MT100 ill just keep using the 1 2x12 and for the dual rec, i'll use 2 plugged into each of the 4 ohm jacks. Thanks everyone.

You could use both if you get a series box. Like this one:

https://www.amazon.com/PALMER-PCABM-Passive-Cabinet-Merger/dp/B00IBJ0C46/

It's actually cheaper than the Mesa one, and also actually IN stock.