"Hey LTD02, just out of curiosity sake....what does the marty sub have over an F-20 other than the obvious few hz of extension and smaller enclosure? Seems like the marty sub has very similar performance but costs twice as much to build."
they are just a little different. the "obvious few hz" might not be so obvious. here's why.
the marty targets 17hz or so. with power and excursion limits coming in at about 117db from that point up.
the f20 is a front loaded horn, so its excursion minimum is actually up around 25hz or so. as a result, even though the response corner is around 19hz, the driver will be up against its excursion limit much sooner. at 17hz, it is about done at 106db and doesn't get up to 117db until about 22hz. from there on up though the slightly larger size and horn loading gives the f20 an advantage of 6db or so on up through the rest of the bass.
the response of the f20 has a little more ripple in it than the marty, but nothing too bad. the f20 is a little more sensitive in its passband, so doesn't require as much power.
the other thing is that the marty has a more traditional form factor and that is appealing to folks who may feel like they are going out on a limb as it is with a first diy attempt.
so they are just a little different. of course, a bigass low tuned front loaded horn with the si driver would outperform them both. that was the thinking behind the submaximus, but that one never get completely completely fleshed out. i'd be happy to work on it with you if something like that is what you are looking for. now we would be talking about 123db at about 17hz, but also about a 4' x 5' x 2' enclosure.