Let me be very clear. I'm saying you don't know what you are talking about. That is my recommendation to the OP.

It is possible to do it, but a dumb idea because it will probably sound like a popcorn fart. It isn't practical because it is a waste of power. MY recommendation is to run only the dual 4 ohm sub at 2 ohms so long as the sub can handle the power.

I was using the bandpass as an example, thats it. It was meant to illustrate a point and I made it clear that in the current situation it would not be possible.

Clear as mud because it doesn't apply to this situation.

Everything you have said thus far doesn't make sense. Technically your idea will work, but my point is that it isn't the ideal way to do it. I won't argue semantics with you it's a waste of time.

To Blaire:

What subs/amp are you running? Let's look at all your options.

ok, so i've got a type r 12" dvc 4ohm, and a type r dvc 2 ohm for the subs. As for the amp we're looking at a alpine mrp m850. At the moment i've got each sub wired seperately to 2 single amps (an mtx 4001, and a mrp m450), which is perfectly fine. I've got plans to get rid of the 4 ohm 12 which im planing to replace with 2 ohm, just wanted to know if it was technically possible to wire them both @ 2 ohms to the m850.

Almost anything is possible. Its only the product longevity/reliability and the sound that will be effected.

22 years ago in my first car I had (9) speakers hooked up to a 2-channel alpine amp. It held together and I didnt know the first thing about series/parallel or impedence loads.

That being said, dont mix & match!

I agree don't mix and match.

Years back I tried a few combinations of equipment in my Grand Am and tested on a meter to see what would happen.
I used individually sealed boxes with 2 8's / 2 10's /and 2 15's in different combinations on 3 separate amps.
I found that if the 2 10's and 2 8's were run together with similar amounts of power(250w each pair) they would be louder than either pair by itself and sounded ok.
The most interesting result was when I wired All three sets in the car. The 2 15's on 1200w and the 10's/8's on 500w combined. It was slightly quieter then just the 15's, and sounded bad. The 15's overpowered the other 4 subs so much that they would almost bottom out even when disconnected. I even tried reversing the phase of the smaller subs to see what that would do.
My conclusions:
mixing different equipment with same power - Ok but not ideal
mixing different equipment with big power difference - Bad!
matched equipment and power - Best
I had way too much time on my hands back then.

I would run just the dual 4 at 2ohms for now

1 phrase comes to mind when your talking about powering 2 subs of different impedences on the same channel.

Path of least resistance.

Meaning the sub with the lower impedence is going to get the majority of the power becuase current flows in the path of least resistance.

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Go with your dual 4 ohm sub for now, feeding it 800 watts will be just fine.

Sorry Blaire we got a little side tracked, seems your only going to get two answers to your technical question as asked.

Sure, technically you can do it, but that doesn't mean you should.