[JCD]

Please take this for what it's worth -- just the advice of someone who's dabbled in DIY, but will never claim to be an expert.

First, the biggest issue to me isn't the number of drivers, rather it's the orientation of the drivers. You'll want them in a vertical line. My general rule of thumb is that, all other things being equal, more drivers is better. The main reasons for this vertical orientation have been listed above already.

If you decide to go with the curved box, I don't think you need to worry so much about building a rectangular box for the interior volume unless the speaker is really shallow. That being said, I'm not entirely sure if there aren't any issues involved -- resonance issues would be something to investigate. Just for reference, of the "normal" shapes, sphere's are actually the "best" enclosures -- and I think pyramids of a minimum angle come in second with rectangular boxes third.

One other issue you'll need to investigate with a curved enclosure is the baffle step compensation you'll need for your speaker. Edge diffraction may be another issue to look into, but probably not more than a "normal" speaker. Finally, just building an enclosure like that is going to be pretty difficult to make look good. Not saying it can't be done, but I know I don't have the skills to pull that off.

The last issue I want to address is the crossover. Building a two way crossover properly is difficult/time consuming/potentially costly. It requires a lot testing, measuring, etc. Going with a three way crossover, especially for a beginner, is nigh impossible. Unless, of course, you go with an active crossover -- which, of course, means you'll need to buy a lot more amps. I'm building a 2 way line array right now and I'm WAY too chicken to try and design a proper crossover for this speaker (I'm going active). Like I said above, I'm not an expert, but I've been dabbling in this DIY stuff for a little while, but this area is way to technical for me.

And please don't assume I'm trying to counsel you out of designing your speakers from the ground up --- I just would hate for you to spend a lot of money on a lot of drivers/crossover parts and spend a lot of time building a speaker only to discover you don't like the end result. I really enjoy the whole process and would LOVE for you to try your design -- I just wanted you to be aware of some of the issues you will need to address if you want it to sound as good as it looks.

JCD