Hi Kilo
Ok, but the Tangbands (you should check out the frequency curves on those things!, pretty flat all the way to 15k, except for a little spike at about 7k) will be crossed over so high, will they experience lobing?
Yes! I get the feeling you haven't quite got the hang of constructive and destructive interference patterns.
Imagine, (or better still try it next time you're in the bath!) two spherical water waves meeting- when then two peaks meet you get a peak of twice the height of the individual waves, and in the troughs, twice the depth. This causes rays of high and low response to emit from a common centre between the two centres of radiation. this is called beaming or lobing.
Now, if you move the two sources closer, this lobing becomes less pronounced, ( it is still there, but the high and low peaks are spread at a wider angle from the common centre), and this is what we try to do when building speakers to give a smooth even response across a wide angle.
However, if you were sitting glued to one spot, or a long distance away from your speakers, you could use lobing to good effect. By careful design, you could focus the constructive interference towards your seat, and destructive interference towards the walls in your room, therefore reducing room reflections to a minimum, (one of the reasons for the current trendiness of line arrays in live music PA).
This will happen with any drivers sharing the same frequency response, even if they are different, say M and T, if the roll off of the crossover is slow, there will be some common frequencies produced by the two drivers, and this will cause interference to occur. This is one of the reasons why a pair of loudspeakers have a sweet spot, and people like me spend ages mucking around with placement and toe in...
However that was the easy part... The real world is not two dimensional, with circular ripples, it has three dimensions, and the waves are spherical! This means that instead of rays of high and low pressure coming from the accoustic centre, we have miss-shapen cones.
But I could waffle on about this for ages...
To get to the point I think I'm trying to make, I think you have two options
1) Just mount all your drivers as close as you possibly can to each other, and it might be worth building a test box with a removable front so you can try different arrangements.
2) Go for simplicity and just build two boxes with a single TMW arrangement, nearly halving your costs, and producing probably a better sound "out of the box" so to speak.
I personally would go for option 1, but that's because I have the time to play, the wood working skills, and I already have a fine pair of front speakers I built myself, and so I am in no rush to achieve success, but if you want to have something you built yourself NOW, to listen to music and show off to your mates, then go for option 2
I'd use a t-line stuffed till it is aperiodic...
Couldn't agree more mate... it's the way to go...