2x12 mesa cabs / Help with impedance

[Dyerwolf4]

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.

 

[bandit2013]

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.

 

[Dyerwolf4]

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.

 

[DECEMBER]

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.

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".

 

[Dyerwolf4]

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".

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.