Dual input for my guitar cabinet

[Sir GuitarCozmo]

Okay, so my cab has 4 70W speakers in it.  What I would like to do is install a dual input jack in it.  Have one jack go to the top two speakers and the other jack go to the bottom two.  Then set up a situation where I have my 100W Randall going to one input and my 50W Marshall going to the other and have them both running out of an A/B switch.  So at any given time I can be playing one amp or the other (or both) and have it come out of the same cabinet.  This seems like something that should be fairly easy to do, but given that I really am not very experienced with speaker wiring and such, can somebody tell me how feasible this would be?

[BlobVanDam]

I'm no expert on guitar equipment, but the only issue I can think of is the impedence maybe? Would it alter the ohms to only run 2 speakers instead of 4?

Aside from that a speaker box is pretty simple. Probably a fairly straightforward job if you're handy with a soldering iron. The plug is easy to buy and will only cost you a few bucks.

[Sir GuitarCozmo]

Currently, the cab is wired for 8 ohms.  I know the Marshall has an ohm selector on the rear of the amp.  The Randall does not.  It just has two speaker outs that indicate parallel output, 4 ohms minimum.

It seems like that should be the biggest problem I'd face, would be ensuring the ohms are all matching up.

[TheCor]

Very feasible...You'll need to look at the speakers to find out how many ohms of resistance each has.  Guitar speakers generally come in the 8 or 16 ohm variety. So if your 4x12 cabinet is rated at 8 ohms, it probably means your speakers are 8 ohms each, wired in series-parallel.  If this is the case, you can wire the two speakers for the Marshall amp either in series (wire the + and - of each speaker directly to the + and - on the jack) or parallel (wire the + of the jack to the + of one speaker, then the - of that speaker to the + of the other speaker and the - of the second speaker to the - of the jack...); parallel will give you a 4 ohm load while series will give you a 16 ohm load.  Adjust your ohm selector on the amp accordingly.  Here's some reference diagrams: https://www.colomar.com/Shavano/2x12wiring.html You can omit the output jacks in the diagrams since you won't need them. 

Since the Randall amp does not have an ohm selector, but requires a minimum of 4 ohms, you can wire the speakers either way for this amp also.  Wired in parallel will produce more output, but will be more taxing on the amp and could reduce sound quality if below the minimum for the amp; but as the amp is rated for as low as 4 ohms, it shouldn't be a problem.  If wired in series it will produce less output but be less stressful to the amp.  Either should really work fine, but series might be a better choice for the Randall since it is has twice as much power, it might help even it out with the Marshall too. 

If your speakers are something other than 8 ohms each just remember that series wiring adds the ohms of the speakers (2x16 ohm=32ohm total load), and parallel halves it (2x16 ohm=8ohm total load).

[Sir GuitarCozmo]

Excellent.  Thanks for the great information.  I think it would be really cool to be able to play either amp at will, since they each have good to offer.  This makes it a little easier for me to "get" what I'm doing.  Hopefully someday soon, I'll be able to put this together.  Now the only other thing to concern myself with (based on what I've read elsewhere) is to put up some sort of wall between the two sides, to completely isolate them from each other.