How do you know I haven't sent it a sine wave sweep?  I wouldn't be lauding it's worth unless i've put it through it's paces.  The driver has an xmax of 16mm so there's plenty of excursion.  My front window resonates at 42Hz, the side ones at 35, the large painting in the hallway (more likely the wall itself) around 25, the dog gets mad around 18, etc etc.  If you want or need more, you can put an Eminence 10 (HL10) in it, throw 300 watts at it and probably do damage to your hearing, your relationships with your neighbors and your criminal record.

If you want a 1 note wonder, build a giant 6th order BP. It's going to sound like crap but it'll be loud.  Have fun trying to blend it with your 3 other tuned wonders and then your mains to get the full audio spectrum.   A Bandpass is just that.  It's a "lets focus our attention at a couple frequences and play the hell out of them and ignore the rest".  What good really is the movie going experience if a girl banging on the aquarium massages your back while the explosion of a bus allows you to hear the phone ringing in the next room?  You need to be able to play way down low for today's LFE tracks but still blend it well with the frequencies in the 40 to 80/90/120 range (basically however far down your mains will play).

I'm building a Tuba36 right now.  I should be done in a couple weeks and I'll have a comparison to that as well.  I'm fairly confident I'll find it blows everything including the TT away.  That the TT can handily defeat the HWK, I can only imagine the orders of magnitude that a Tuba36 would outperform a HWK and do it across a MUCH wider range.

You may be right Bob on the reference point issue.  I've spent a good number of hours and days reading up on enclosures and theories behind them.  I'm in no way claiming to be an expert and anywhere near the knowledge or experience of most of this board and certainly Steve & Bill but I know what I like.  The theory behind horns just makes sense.  A horn (as it's been explained to me) is basically an acoustic leverage device.  A small driver exciting alot of air at one end will excite a large amount of air at the other end of the horn thanks to an exponentially expanding throat.  That's why you don't need a huge driver and kilowatts of power for huge sound.  The imperial cabinet is a type of horn and you see how much everybody here loves the bloody things.  I just don't have the room or I'd probably build one or two.

What I've found in practice supports my opinion that horns rule, a good sealed box will work if you can't have a horn, vented if you're desparate and bandpass if you're only concerned about SPL drag racing.  

Every few months someone brings up the tuba designs and I can't remember why I didn't like them so I check the site again and remember very quickly.

Even on the largest tuba, lf rolloff starts around 40 hz and is down 10 db or more by 20 and still dropping hard, measured for corner response.  You would have to stack at least one more, and probably 3 more, to get close to flat down to 20.

There are much smaller, albeit less sensitive ways to do this.

I've read reports of the WO going flat to 27.

If you want a traditional horn flat down to 15 the mouth is going to be roughly the size of the cross sectional area of your listening room.

With Adrian's comment, I can't help but think of the old schoolyard days... "fight fight fight fight!!"  :)  I think if John weren't in CR and I weren't in FL and Bob wasn't wherever he's located, we probably would!  :)

Extending the HWK, aside from looking kind of ghetto, is still going to suffer from the same problem of being a 1 or maybe 2 note wonder.  Increasing the chamber size is going to change the tuning, obviously, but it won't rectify the issue.  

I'm not building the Tuba36 to replace the TT, I'm building it as an experiment and for a different sound system.  Bassboy mentioned it rolling off at 40Hz and down 10db at 20 hz and it keeps going. The vertical baffle is maybe 10db down at 15 hz and not down quite so sharply.  What's not mentioned is the scale.  10db down from 130db is still 120db.  A little EQ will flatten that out very nicely.  

Bassboy, what are the smaller ways to accomplish the response we're talking about?  I'd like to read up on them if you have some links.

Bob, try the extension.  We're all in this to learn and debate (on occasion) our ideas & opinions.  If it works for you, wonderful. That knowledge will help the next guy who comes along with a similar issue.  If not, at least we know, so same deal.  

John, you keep mentioning the TT's size.  It's not really that small. The enclosure is 30X30X16.  That's about the size of a WO or WO32 give or take.  I've got some woofers intended to go into a WO and I will be building one in my quest for the ultimate sub.

Trashfire,

Now you are just pulling numbers from the air.  Bassboy is probably correct that those predicted responses on Bill's site are with corner loading.  Plus all of the ones I looked at cut off at 20hz.  120db at 15hz, come on get real, 90-95db max at 15hz, maybe.  You really need to talk to Bill instead of just making things up off the top of your head.

There are no links to the kind of stuff you are talking about because it doesn't exist.  Sealed with Linkwitz transform, big vented box, and giant horns are how you get down really low.

While a 6th order bandpass can be a 2 noter, it doesn't have to be.  I built several HWK 12's for friends and they all worked fine with reasonably flat response from 40-100hz.  All I want is the same octave and a half, but starting as close to 10hz as possible.

Trashfire,

Don't get me wrong.  I firmly believe that horn bass and OB bass are the 2 best sounding ways to make bass.  It's just that neither is practical once you start talking about real HT extension and getting the performance level where you never feel the need to build yet another sub.  If subsonic extension was reasonably achieveable using horn loaded enclosures, then no one would build anything else.

If anything near 120db at 15hz was possible from a 36"x36"x20" single 15" horn or even the 36" cube dual 15" Tuba 36, I'd start building tomorrow.  Just filter or EQ the higher response down to flat and you'd have the ultimate subwoofer for music and HT.  Unfortunately, the laws of physics get in the way.

Dude, are kiddin' me? I guess that would fix it.  ;D I could fully load a HWK for just over $2,100.   That's friggin' dandy.  :-X

Ok, back to reality...... (Adrian, got a couple grand I can bum?)

JOHN HELP... I "played" with WinISD for 'calculate box dimentions', and it said this version can't perform this task. WTF?!
You got me all worked up and exited now John.

Bob

Bob, you could try to simulate in winisd a vented box and choose the EBS alignment. -3dB version i guess. ebs is a pretty good choice for ht.
another idea would be to look into TLs.