Hi Frankx,
As I said before I am a bit afraid to build a totally new tipe of enclosure like the open baffle (I have no experience with that type of speaker)
A closed or ported box can be just as difficult to design as an open baffle. If you read the Linkwitz website he goes into great detail on how to do this.
isn't true that open baffles needs veeery big woofers to reach a good levels in the low end?
Yes and No. You need drivers capable of large excursion. But my woofer frames are essentialy these.
http://www.linkwitzlab.com/proto.htm
The dimensions are approx. 26"Hx14"Wx12"D. Probably MUCH smaller than the enclosure needed for a KappaPro 15"! The drivers are 4x12"
http://www.partsexpress.com/pdf/297-608.pdf
You will not hear clearer more natural bass than this. At first listen you think something is wrong - because you are used to hearing a "box". It is upon further listening that you realize the superior naturalness of the bass. The boom,slam,etc is gone. Again, you will not have heard clearer cleaner more natural bass. You really have to hear it to understand. But don't just take it from me. I have owned many, many speakers, boxes, planars, etc. Look at the list this gentleman has owned. Listen to his comments. I agree 100%.
http://www.doddsy.net/steve6_009.htm
Now, unfortunately Frankx, I think a LARGE part of your problem is your room! 3m means that your speakers are probably close to if not touching your rear wall! With a monopole speaker like yours, you have a huge imbalance in the power response already. The bass range probably exceeds your treble by 15db - or more. You are also sitting "near" field from your speakers, probably about 2m or so. Not always good. The dipole would certainly be superior here. Less boom. Remember with a compact cabinet like mine, you can slide the speakers out say 0.8m into the room, give it a little distance from the rear wall, when listening. Then push them back against the wall when done, or when the wife yells at you (dipoles tend to be MUCH lighter, because you have no box!). The bass will be plenty! You would probably also have to deaden the wall a bit behind the mids. Its hard to say. The problem is integration of your mids/highs at such close range. Again I suspect this is part of your problem. the nice thing is that you have a DCX. This will certainly help. Perhaps you should consider a coaxial driver. They integrate extremely well at close range because of their point source nature. There are some very nice Pro models. I hesitate to recommend them because I only have first hand experience with a few. These I have heard
http://www.radianaudio.com/products/ceiling/8_ceiling.php4?viewT=ceiling&viewC=8_ceiling&viewI= sound very nice. They don't have the absolute refinement of the SEAS/Vifa that I use, but still quite dynamic. Maybe some other members here can comment on these
http://profesional.beyma.com/ENGLISH/producto.php
There are also some nice ceiling units (YES) like these
http://www.kef.com/products/ciseries/technical/ci200qr_tec.html
that can be used OB.
Or these SA-15R
http://www.paradigm.com/Website/SiteReferenceProduct/RModels/InWall/SA_Specs.htm
can't say what will be available for you. Again perhaps other members can suggest others.
I hope I at least gave you some ideas to consider.
Gotta run.
Cheers & good luck
AJ
btw, just to be clear, I'm suggesting ceiling speakers because they are very suitable for open baffle, since they are intended for infinite baffle scenarios.