Suggestion request for flat 20-55hz

[PloppyThirds]

Howdy, I recently received access to a large cnc table router and supply of baltic birch and mdf. If materials and construction were no object how would you design a box with flat response from 20-55hz? Dsp processing is an unlimited resource as well, delay phase equalization etc. can all be modified at will thanks to some heavy handed online shopping but I'd like to make the box as efficient as possible.

 

[GM]

Big A$$ compression horn does it all, but the size for 20 Hz........ so need to at least set a size limit, ditto driver budget if woofer system needs to be very efficient in a relatively simple cab [relative to a compression horn].

GM