Hi Willy, excuse me this late reply seems I have missed your post 
Golden ratio enclosures always good, it dismiss the use of internal bracing, mirror image also good, but even the mentioned 10L enclosure goes only to 75Hz what is too discreet bass performance to a satisfactory listening, hence this I would go with the Frugal Horn as Suggested by Dave, in second place a even bigger Bass Reflex box to additional bass reinforcement.
Seems the SB12 can delivery more bass(Fs 52Hz) than the SB10 Fs89, Iam thinking in fullrange use no subwoofer.
Hello, no worries, and thanks for your recommendations.
After further consideration, it seems 10L golden ratio will not work for the intended space. Further, I see not much change between 4-5L and 8-10L in terms of Qtc and frequency response. So I might just go with the smaller volume. In the future I am planning to add midbass, crossed over at the line level, passive or active is still to be decided.
Thank you!
