Yet another cab question

[mike_sims]

So for an upcoming event I've decided I'm going to be using 3 cabs with 2 Model T heads (via A/B/Y box). My question pertains more to this Marshall cab I'm gonna bring into the mix. In the back, there's a switch for Mono/Stereo options. 2 Jack inputs, L (16 ohms) R (4 Ohms) I believe. With the stereo option switched, each input is 8 ohm. Now, here's my question. I wanted to chain my 412L (8 ohm) to the Marshall (presumably 8 Ohm if the Stereo option is switched on). Basically, I'll cut to the chase here, Would I be able to use the 8 ohm stereo option with just 1 jack being used? Of course, I'm going to put the Model T on 4 ohms to split the resistance between the two cabs. Kind of a noob question, I should know this...

[Isaac]

In stereo mode, the Marshall is, essentially, two 8 ohm 2x12" speakers in the same cabinet. So yes, you can use the 8 ohm stereo option, but you're going to get sound out of only two of the 12" drivers. Additionally, those two drivers will be getting the same amount of power as the four drivers in the 412L, so each Marshall driver will get twice as much power as each Sunn driver. They'll be a bit louder than the Sunns.

[thehornedone]

You could always set your model T's output inpedence to 8 ohms.  Then, use one input out of the amp to a 412L (8 ohm impedence), and then use the second amp speaker output for the marshall cab, going into 16 ohm mono.  Going from 8 ohms out of the amp into 16 ohms cabinet input impedence should be safe , but may cut the volume a bit.  If you went from 16 ohms out of the amp to a 4 ohm cab, then you would have a problem.

You can't really match impedence with the 412L and the 1960A.  There is no 8 ohm option for all 4 speakers, and if you're only going to use 2, like Isaac said, they will be getting twice as much power, and might not be able to handle it.  Also, The G12T-75s in the marshall cab have a relatively low speaker sensitivity, especially compared to the 412L speakers.  This will factor into the volume disparity. 

There is always the third option, which I would recommend over the others:  run both 412Ls out of one model T set to 8 ohms, and use the other model t for the Marshall cab.  This would yield the most control for volume balance between all the cabs, and all impedences are perfectly matched and safe.

[Walt-Dogg]

The best way is described  above. As both 412L cabs are 8 ohms I'd assume (as mine was) then set the Marshall to 8 ohms a side stereo and set both Ts to 4 ohms, parallel a cab and a side of the Marshall together with each head. Mike do you plan on doing a tower or a wall or a stereo sweep on the stage with each cab?