"Folded" Sonotube TL Sub Complete!

[bwbass]

I just put the finishing touches on my sub project and wanted to share and get some feedback.

It's a "folded" TL design, using a 12" sonotube nested concentrically (well, eccentrially, I suppose) inside a 16" sonotube. There's a 4 1/4" gap at the bottom of the smaller tube, which makes the "bend".

I had initially wanted to use 14" and 20" tubes, since the CSA's of both sections are nearly identical this way, but found that these sizes are uncommon and hard to find (and really big). I was skeptical of having the area of the first and second sections of the line differ, but after modeling the line in MJK's Tl Sections sheet, I found that the response actually looks quite good, with a broad flat fundamental peak from around 22 Hz to 65 Hz.

The design is intended for the Ascendant Audio Atlas 12, which I don't have yet, so sitting in for it now is my old Phoenix Gold car sub, which has a higher Q but nearly the same Fs and Vas specs.

So far, I'm quite stunned with the performance, especially considering the low cost. Bass is clean, powerful, and smooth, and extension in my relatively small listening room seems limitless!

The whole thing stands about 75" high; line length is 147".

[bwbass]

Here's a shot looking down the line from the top. The first half of the line is stuffed with about .5 lb / ft^3 of Dacron fill. I cut and wedged some 5/16" hardwood dowels sideways across the tube to keep the density even and prevent the fluff from all settling to the bottom.

[bwbass]

This is my favorite part of the whole thing... the inner tube is just bolted to the outer one with some big old binding posts from Parts Express. The Atlas has two voice coils... one for driving and the other for adjusting the Q via resistive damping, so I put two posts at the top (for the RDO coil) and two at the bottom for the driven coil.

The finishing touch was some nice neoprene-backed sealing washers from Home Depot. Airtight, and solid to boot!

[Tweeker]

$#@%! you beat me to it! Very nice sub. Im building a concentric sonotube tl too, but have a few too many other to dos to do on my to do list. Im having trouble finding the tubes I want too.

4 out 5 five people polled cant say the name of your city right

[bwbass]

Originally posted by Tweeker
$#@%! you beat me to it! Very nice sub. Im building a concentric sonotube tl too, but have a few too many other to dos to do on my to do list. Im having trouble finding the tubes I want too.

4 out 5 five people polled cant say the name of your city right

Thanks!

What sizes of tubes are you considering? I'd recommend the heavy-walled versions if you can get them, as mine is a bit more flexy than I'd like... no rattles or offensive resonances, you can just feel quite a bit by putting your hand on it.

And people around here, against all logic, say "pew-AL-lup". That's where I work; I actually live in Olympia, which is much easier to pronounce.

[zobsky]

good job

[Tweeker]

My grandfather lives in Shelton, fairly near Olympia. Was thinking about something crazy big before (20, 28sleeved30, 36) but it'd be an insane pain . Looking at 16,22,28 now. Plan to run bracers along the tube lengths tieing the tubes together for much more rigidity. Driver is mounted ~1/3 way along the line at the junction. The cone/motor forms part of the first turn. Driver is Avalanche 18.

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You might be able to make your sub much stiffer by bisecting or trisecting the outer tube with a couple boards and glueing/nailing/poswting/screwing them on each side to the tube face.

[bwbass]

Originally posted by Tweeker
You might be able to make your sub much stiffer by bisecting or trisecting the outer tube with a couple boards and glueing/nailing/poswting/screwing them on each side to the tube face.

Meh, it doesn't really bother me that much. I don't think the vibration is caused by pressure in the line, it's more the mechanical motion of the driver making the inner tube want to oscillate around the point where it's joined to the outer wall at the top.

I may get inventive and try to knock a wedge-shaped block under the edge of the small tube in the bend, bracing it against the floor. Have to find a way to do this on the end of a 7-foot pole, though!

Driver is Avalanche 18.

An Avalanche 18?!? Woah.

That's got a 16 Hz Fs, right? How long is your line going to be? My math says 17.5' or so...

[bwbass]

16 - 22 - 28? Isn't the middle section of your line going to be narrower than the two ends?

I get about 1.07Sd - 0.91Sd - 1.17Sd, not accounting for bracing.

[bwbass]

Originally posted by Tweeker
You might be able to make your sub much stiffer by bisecting or trisecting the outer tube with a couple boards and glueing/nailing/poswting/screwing them on each side to the tube face.

Sorry to keep replying to my own thread, I'm just thinking out loud...

You know, adding a board as a stiffening brace is a pretty good idea. If I just do one at the widest point of the crescent, maybe a foot long, I could wedge it in there and attach it with screws without having to take anything apart. And narrowing the line at the end a tiny bit with the brace can only lower tuning and smooth out the response a smidge, both of which are good things.

Thanks for the great idea!