Pearless, Sea or Vifa ???

[v-bro]

[ Or a sphere in a sphere, the driver in the centre sphere and a hole in the outer sphere larger than the driver....the two spheres held together by distance blocks...could be a TL or a BR...

Offcourse there ought to be a hole in the backside of the inner sphere as well...

It's a good idea to use sand to ajust my box volume. I guess that'll give me a good idea of how a smaller box will sound.
REALFLEO

Well to be honest, it's not my idea, many commercial designs use 'dummy compartments'. I've had Mission 742 (if I remember correctly) floorstanders, in the user manual was described this volume should be filled with sand (it was at the bottom end of the cabinet...) so the speaker would gain some stability....

I think I'll try different volume and I'll build another prototype after some listening tests.
REALFLEO

Good idea, perhaps you can make it about 10-11 liters and discover it will have pretty good bass, making the eventual speaker about 15 liters....so you will have experimented with both too large and too small enclosures

No I would say make it 15 liters right away and decrease the volume to test.....

I noticed there is not enought bass with my oversized box...
Can you explain it ?

That's very well possible, the frequency curve might show pretty good subsonic peaks but the general bass response will probably suffer serious energy losses. (i.o.w. probably the audible bass response will show serious dips...)