2-way bookshelf speaker

[XizzeriA]

I recently decided to make a 2-way bookshelf speaker for a big project in school. Earlier I've made a subwoofer and a center speaker, both with good results. But this time I would like to go even more serious.

For bass/mid I'm thinking of chosing a Vifa 6.5" driver, perhaps the MG18WK-09/08 (http://www.d-s-t.com/link/vifa/data/mg18wk09-04d.htm), or maybe the more expensive XT18WH09-08 (http://www.d-s-t.com/link/vifa/data/xt18wh09-08d.htm). Which one would you recommend me? The first one is rather cheap - ~38€ + VAT & shipping - the other one costs ~51€. It's supposed to play together with the 1" dome PL27TG35-06 (http://www.d-s-t.com/link/vifa/data/pl27tg35-06d.htm), at ~23€.

The box will be about 15 (max 20) litres and ported. My calculations tell me a theoretic f-3dB point will lay at approx. 55Hz. Perhaps that could later be changed through the crossover config, but that's a later issue.

Lots of text about nothing (I'm new here...), but I'd really appreciate some guidance here: Should I go with the cheap alternative or does it make a big difference with the more expensive driver? I'm pretty sure the treble will suite me at least. Any other comments/advice is of course welcome as well!

[xyrium]

The Peerless midwoofs (CSX 850122) seem to be pretty popular, and you could cross them over low if you use a Seas 27TDFC tweeter. This will give you an easy range for both drivers to operate within, as well as a good center to center distance. 15-20L should be fine with this setup with a 2kHz xover from what I've seen from other projects..

[XizzeriA]

But on the website it says that the Peerless driver is discontinued, so it might be hard to get hold of. I was looking at Vifa because I feel I get a good deal if I buy them from http://www.audiocomponents.nl/

So, does anyone have any experience or comments on the drivers mentioned above? I like the high sensitivity of the bass/mid driver.

Also I have a question considering the design of the box: How important is it not to have parallell walls in the box? I've heard it could cause waves to just go back and forth (don't know the term in english). On the other hand it would be very difficult to make a box with no parallell walls, therefore one may chose to slope the front or side wall? What are your experience/suggestions?

Thankful for all help I can get!

[XizzeriA]

If there are no opionions, then maybe someone could tell me where to find good info about a drivers Thiele/Small parameters, or generally about loudspeaker design. I'm not into putting 100$ on the last revision of the Loudspeaker design cookbook so a URL or two would be great!