After I decided on the geometry of the speakers, the actual design of the box itself was pretty straightforward. A lot of design aspects are already determined by the TL geometry, thus that makes the design a lot easier (or more difficult, depending on your point of view...). About the only thing I needed to do was to determine the place of the tweeter. For this, I used the baffle diffraction simulator by Paul Verdone. With this excel sheet it is possible to study the effects of driver positions on the output of the speaker. The woofer position is fixed in my case, because of the TL geometry, so the only thing i needed to do was to determine the position of the tweeter. Placing the tweeter as much to one side of the speaker as possible turned out to give the best results. The further I placed the tweeter away from the woofer, the better the results the spreadsheet gave were. However, placing the woofer and tweeter far apart spells trouble in crossover design. This was described (among others) in the AES paper by Linkwitz on active crossovers for non-coincident drivers (1976). It is almost always the best choice to put the tweeter as close to the woofer as possible, however I left some space between woofer and tweeter, because placing the woofer and tweeter close together resulted in a large bump in the response around 1200-1500Hz. And indeed, this came around and bit me in the ass when I designed the crossover, so next time: woofer and tweeter close together and only check the effects in the excel sheet of offsetting the tweeter.
The design(all dimensions in mm):
I also made a drawing of each individual panel in the speaker, with comments in dutch. Click here to download the PDF.
This doesn't give a good impression of how the speaker will look, so I spend an evening with a 3D package and that resulted in this picture:
Not only does this give a visual impression, but it also makes you "build" the speaker. And some design changes are a direct result from making this 3D drawing, because it was clear that some small changes would make sure that the speaker was a lot easier to build.