Cab Impedance question

HHwarner

I think I know the answer to this question but thought id ask to be 100% sure. I have a 4x12 @ 16 Ohms cab and a 2x12 combo @ 8 Ohms. If I run the combo through the 4x12 and its own 2x12 I will get a total Impedance of 5.33 Ohms with un equal power sharing. The 2x12 seeing 66.7% and 4x12 seeing 33.3%, a differential of around 3dB. So this is my question, the amp has 2 parallel speaker outputs, to balance the outputs, could I run an attenuator at -3dB for the 2x12 and go straight into the 4x12 from the second speaker output? I guessing it would work???? Also what impedance setting would be best to use on the amp, 8 Ohm or 4 Ohm as either way its going to be slightly mismatched. Its a Marshall 2104 btw.

ICBM

Don't worry too much about it. 3dB is not a lot, you'll probably not even hear the difference in volume, especially as the 1/3 of the power going to the 4x12" then has twice the number of speakers which increases efficiency by 1-2dB, so the final volume from each cab will be about the same.

Impedance matching is not critical unless you're really thrashing the amp, and even then a less-than-2:1 mismatch either way won't cause any harm. Simply connect both cabs to the amp and set it to either 4 or 8 ohms, both will be fine although they may sound slightly different.

If you do want to try it with the attenuator, remember that the amp sees the attenuator as the load and not the cab, so treat it in the same way as if you have two cabs, the 4x12" and another cab of whatever impedance the attenuator is - if switchable, set it to 16 ohms and the amp to 8.

HHwarner

Thanks IC. Ill give it a whirl without the attenuator. I did wonder about the perceived difference in volume being minimal as the number of speakers in the 4x12 are double that of the cab receiving 2/3 of the power.