I currently have a passive 3-way speaker, and I have 2 extra morel, 8 ohm midrange drivers which I would like to add one to each of my cabinets so I have two midrange drivers in each cab. I am not too keen on the idea of adding them by wiring in parallel creating a 4ohm situation as the crossover I have is rated for 8 ohms. Could I run a separate band pass filter for the extra midrange and if so how would that band pass filter be wired with my existing 3-way crossover in my cabinets
There are many reasons, acoustic and electrical, why you shouldn't do that. In general, two midrange drivers in a speaker will not be twice as good as one. Their sound will interfere with each other, creating additions and cancelations, making the all important mid range sound uneven. Even worse, this unevenness will vary as a listener moves his head or sitting location.
In your case, you have a 3-way speaker cabinet and crossover designed for one mid range driver. I can't imagine how adding another mid range could improve it, but I can list many ways it could make it worse.
You've already realized that the impedance will be altered by adding another driver. The crossover's function will change significantly if you change the impedance of the drivers.
Where will you mount the second mid range driver? You have a 3-way speaker designed from the start to have one mid range. It's likely that those 3 drivers are mounted in a vertical line, woofer on the bottom, and tweeter on top. There are good acoustic reason's for maintaining that vertical arrangement. And it may also be that the crossover was designed with the drivers mounted that way. Changing locations of drivers on the speaker's front baffle must be accompanied by a redesigned crossover.
Is there a problem with the sound of your 3-way speakers? If so, I doubt if slapping in another mid range drive can improve it. This is a case of "If it ain't broke, don't fix it."
