John are you teasing me?

Bob

Bob do not get rid of the HWK. Just build another sub, of course on a budget, to complete the circus. WO36, WO32, or some of John suggestions that could be located in front of you to play lower bass than the HWK and use the HWK to fill in what you might be missing(50Hz to 100Hz). The klopping noise is the speaker being over driven to the point of bottom out just like the others said. With the amp only turn up a quarter of the way it seems that you gains on the receiver might be set to high. Not that I am the master of adjustment but when I play the movies you talked about with excessive gain on the receiver my HWK15 sounds like the "Budweiser Beer Wagon" pulling up to the front door and loudly I must say(klop/klop/klop). Just my "Brain Wiped" two cents.       HT-EXT

Bob,
I wouldn't even worry about WinISD, since it won't model the center chamber.  Just go with Dan's dimensions for the big chamber and build it with an extension to your current bottom chamber.  To get it to his size just do the following (You'll need a sheet of plywood plus enough for say 3 or 4 shelf braces similar to your current driver cutout baffles, but only 1 thickness is needed, and a new end cap, same as your current one but the new interior dimension will be the same as your original cab exterior dimension):

Cover the 2 current bottom port holes from the inside.

Cut 4 side panels-  48"x (current exterior width + 1 material thickness).  I go a tad wider, then use a flush bit for the router to perfect the edge after assembly.

Cut 3 or 4 braces-  Original cab exterior width X depth.  Make a big cutout for air flow (driver cutout size should do the trick).

Now if you didn't do wrap around assembly the first time, you get to learn the easy way.  Attach the braces to one panel, flush with one edge.  Then, starting at the non-flush edge, attach the other panels one at a time to the existing panel and braces by wrapping them around the braces.

To make it so you can take it apart and get to the bottom driver but get a good seal, build a sealing ring on the interior of the new construction 4" from one end.  Say four 1" peices of material forming a ring around the interior, 4" from the end.  Using foam rubber as a gasket on that ring, it will give you a seal when you slide the end of the original cab into the new construction and attach it with screws.

Build your end cap the same way as the original.  I'd put the port in the end for simplicity and go with a temporary straight port at first and try a few different sizes for desired tuning, starting with Dan's recommended 4" by 17".  You'll probably settle on something a little shorter (higher tuning), since the other end is tuned a little higher than Dan recommended.  Once you get the tuning you want, buy flares for both ends.  I'd replace the coffee can port with a real flared port too, unless it has zero port noise.

That should give you impressive extension, eliminate the whacking noise, and make you feel like you're inside the fish tank when Darla taps on it in Finding Nemo.  If you still have some excursion problems at very low frequencies, then you'll need to tune coffee can port lower with a longer port.  Your current banging problem is most likely with your current bottom driver and chamber, not the top, so the new big chamber should resolve it.

Bob,

You got the idea, but I think more exactly 7' 10.25" with top and bottom caps and using the current bottom cap as a brace and cutting a big hole for air flow.  You have room to lay it on it's side right?

I wouldn't even take the drivers out or disconnect them.

Maybe save the padding for another project, or leave it there.

We haven't talked about your mains.  Do they go low enough to work with a sub that only goes up to 40-50hz ?

82 dB sensitivity on the RL-S sucks hard.

Well, considering your 89 dB will get as loud with 300 watts, you should feel proud. lol.

I mean, full wattage the RL-S thing will ony go to 122 db. (without the box in the equation....)

Ok, John let me make sure I've got this correct.

-Build your idea as planned.

-Don't "SEAL" the double ports permenantly on the old HWK.

-You said; "Put them both behind you firing at each other and the ports firing into the corners resulting in some extra down low." --- You lost me there. "AT each other, but ports AWAY from each other?"

-Does the new box have the 3 ports just like Steves, or eliminate the doubles in the second build? The single center port would be 4" X about 17"?

I've modded this reply seven or eight times, got frustrated, removed it once, and started over.  >:(  Just when I think I've got it straight, and only have a couple questions .....  :o ? bla bla bla.


I THINK I'm with you John

Bob