Hi Frederik,
Love your design, its very similar in many ways to my double 14" design which is also sealed. Its also similar to Seeburg's K24, except they have ported the the LF and I don't like how the 12" speakers have 2 entry point into the small horn. (see the link below)
If you look carefully at their directivity plot, you can see the advantage of getting the crossover point a bit lower if your HF driver can cope with the extra load.
http://www.seeburg.net/download_getfile.php?file=downloads_EN/06-Datasheets/K-Series/K24_Datasheet_engl.pdf
My idea for the dual 10" or 12" was very similar to your design and the K24. I was going to port it like the K24 to get a bit more LF.
Here is the frequency response of my double 14" on axis, at 45 degree horizontal and 20 degrees vertical ... ignore the lumps and bumps below about 250hz, there were some ground reflections etc. and I just did a quick measurement to check the directivity around the crossover at 650hz.
[ATTACH]208446[/ATTACH]
