as with all things, learn from the masters. figure out what they are doing and why. once that is achieved you will be in a position to take the next step. otherwise, you are just lost in the same space that they were lost in.
go to danley or even bfm. model their work. once you can and understand why, you will be ready for your green belt. everybody thinks they are a black belt just because they learned something that was new to them. that is learning, but only to the self. in order to be a black belt, you have to either have a total command of the current learning or have something new.
an example of something new is how danley puts two horns together in the cinemonster. each horn alone would be good enough, but when you couple two tapped horns you get a litte bit more than the sum of the parts, which is what happens with the th221.
unfortunately, there is very little room for "pushing the envelope" in subwoofers. the science seems to be fairly well worked out and the driver and amplifier parameters are what they are. the more that it all gets figured out, the less "exciting" diy will be as the surprises will be very small.
klippel and co are working much harder and with more resources to identify the leading 'edge' of subs. almost all the pro audio subs follow the same model because the science is worked out.
if you think that you can find something that they have all missed, that would be awesome, but is also extremely unlikely. most of your "creative ideas" have been tried long ago. this is not meant to discourage you, but to humble you by sharing that we have all gone down the same path. welcome to the realm of rigorous science.
my advice is that if you really want to beat a master, select one of his best appications. develope and understanding of it on all dimensions. then beat it if you can.
