I have a "stock" HWK15 with two Dayton Series II drivers in it (currently mounted one in each baffle, magnets in).  This cabinet has been sitting unused while I directed my attention to my main system - the bottom end of this consists of a pair of EVX-180B drivers each in their own reflex cabs, and these extend nicely down to 32 Hz.  Now, I want to revisit the HWK to see if it can be appropriately modified to cover the bottom octave down to the high infrasonics (16-32 Hz, and if possible, even lower).  As it will be dedicated to this frequency range, the obvious things to do (exclusively, or in combination) are:

1) clamshell both drivers in the bottom baffle for the lowest possible chamber tuning,
2) extend port lengths to lower tuning,
3) modify the upper lid to provide additional chamber volume,
4) replace these drivers with a pair more suited to producing this octave.

I was just curious if anyone was doing something similar, and if so, how you managed to obtain the desired response?

-Sean