2x THTLP build after a 10 year hiatus

[shawn_g]

It's hard to believe it's been nearly 10 years since my last build! I built out our unfinished upstairs/attic and have been using a pair of T39's (from my signature) as makeshift home theater subs. They sound great, but they're obviously not designed for HT use and drop off below 35hz pretty quickly. When I framed the area behind my TV, I specifically made enough room for two THTLP's to go there and the time has come to build said THTLP's. Once these are built, the T39's (cabs only) will probably be up for sale if anyone is interested (SE Ohio).

I'm going with 23.5" wide panels to maximize plywood use (1/2" Arauco) and am hoping to build both cabs with 5 sheets assuming I don't make any really dumb mistakes. So odds are I'll be purchasing a 6th sheet

I'm reusing the Lab 12's from the T39's. I'm going with the "extended surround drivers" option in the plans to potentially use 15's in the future so I'd only need to build a new mounting panel instead of a whole new cab, but I'm fairly confident the 12's will be plenty.

So first the space in question. The subs will go behind the TV and you can barely see the edge of a T39. For reference, the TV is 85".

Getting started on first cab:

Using my MPCNC for the 2/6 braces. You can see failed attempt #1 in the top of the frame:

Making some good progress:

CNC to cut out router templates for the curved mouth braces:

That's all the progress for now. I'm hoping to get them finished within the next few weeks. They'll be finished in Duratex.

[Tom Smit]

Good progress so far!

[88h88]

Are you sure the structural integrity of the room will be able to withstand 2 of them flexing way down in the hz?

[shawn_g]

Good progress so far!

So far, so good!

Are you sure the structural integrity of the room will be able to withstand 2 of them flexing way down in the hz?

I sure hope so! lol

I got panel 9 and the 4/9 braces installed on both cabs last night. I forgot how time consuming the braces can be!

[Joman116]

Good progress so far!

So far, so good!

Are you sure the structural integrity of the room will be able to withstand 2 of them flexing way down in the hz?

I sure hope so! lol

I got panel 9 and the 4/9 braces installed on both cabs last night. I forgot how time consuming the braces can be!
PXL_20260306_002510085 (1).jpg

Looking good. Where are you finding arauco acx?

[Keryn O'Shea]

..I specifically made enough room for two THTLP's to go there and the time has come to build said THTLP's..

I really enjoy seeing these and the T60s come together

Are you sure the structural integrity of the room will be able to withstand 2 of them flexing way down in the hz?

They'll definitely test it, possibly some dust in the air for the first couple of digs.

Using my MPCNC for the 2/6 braces.

I find this gadget very interesting, thanks for sharing.
In regards to finish in the mouth area, are you using Duratex & painting before the side is attached?

[shawn_g]

Looking good. Where are you finding arauco acx?

Menards always has it. I'm not sure you have Menards in Texas though.

I find this gadget very interesting, thanks for sharing.
In regards to finish in the mouth area, are you using Duratex & painting before the side is attached?

The CNC is pretty handy and didn't cost much to build. I'm happy to answer questions about it if you have them. Regarding paint, you'll see in some of the photos below, but I spray painted the mouth area before the side went on and will apply duratex to the areas I can get to.


I got a fair amount of work done this weekend. Panel 10 in both cabs and all braces installed. Whew!

A little spray paint in case anyone ever looks under her dress I'll duratex everything else I can reach with a roller.

Side covers attached!

I've got one driver in, but haven't got the cover flanges, cover, or chamber braces made yet. I'll probably work on that tonight if I get a chance.

It's been fun so far. I forgot how much I missed doing this.

[DaveMacKay]

Makes me wish I had room to add more. You’re doing a great job on the build.

[shawn_g]

Makes me wish I had room to add more. You’re doing a great job on the build.

Thanks a lot! I knew these would be large based on photos of others, but it's crazy to see how big they are in person!

[Joman116]

Looking good. Where are you finding arauco acx?

Menards always has it. I'm not sure you have Menards in Texas though.

I find this gadget very interesting, thanks for sharing.
In regards to finish in the mouth area, are you using Duratex & painting before the side is attached?

The CNC is pretty handy and didn't cost much to build. I'm happy to answer questions about it if you have them. Regarding paint, you'll see in some of the photos below, but I spray painted the mouth area before the side went on and will apply duratex to the areas I can get to.


I got a fair amount of work done this weekend. Panel 10 in both cabs and all braces installed. Whew!
PXL_20260307_193824466.jpg

PXL_20260307_195110315.PORTRAIT.jpg

A little spray paint in case anyone ever looks under her dress I'll duratex everything else I can reach with a roller.
PXL_20260308_164110288.jpg

Side covers attached!
PXL_20260308_183654515.PORTRAIT.jpg

PXL_20260308_183705195.PORTRAIT.jpg

I've got one driver in, but haven't got the cover flanges, cover, or chamber braces made yet. I'll probably work on that tonight if I get a chance.
PXL_20260309_005924164.PORTRAIT.jpg

It's been fun so far. I forgot how much I missed doing this.

Looks great. What method are you using to get the "width" panels perpendicular to the side panels? I created right angle jigs with two sheets of plywood, but they are no perfectly 90 degrees.

Also, let me know if you ever plan to sell the lab12 drivers...I need another one for the second Tuba60 I will build later this year..

[Tom Smit]

Looking good, Shawn.
You're correct. They are not small.

[shawn_g]

You're correct. They are not small.

Ha, no doubt about that! I about knocked one off the table trying to rotate it myself on Sunday

------

I wasn't overly productive last night, but I got the cover flanges installed on both cabs and the chamber braces installed on one cab. Tonight I plan to install the rest of the braces and make the chamber covers. The jagged screws holding the cover flanges will be removed and holes sealed.

[shawn_g]

Looks great. What method are you using to get the "width" panels perpendicular to the side panels? I created right angle jigs with two sheets of plywood, but they are no perfectly 90 degrees.

Also, let me know if you ever plan to sell the lab12 drivers...I need another one for the second Tuba60 I will build later this year..

Thanks for the compliments. I cut as much as I can on the table saw with known square edges against the fence. I also used a homemade crosscut sled for some of the cuts. On the large panels that are too big for the table saw, I use a cheap track saw that I got off Amazon years ago.

I use a lot of plywood scraps to keep the panels perpendicular once they're in place. I'll measure the distance between the panels at the bottom (the side panel where all the layout lines are drawn) and use a plywood scrap at the top making sure the measurements stay the same between the top and bottom of the panel. Also be careful when installing braces because it's easy to make the panels get wonky if you wedge them in too far or not enough.

You can see my plywood scraps here keeping panels square:

[Joman116]

Looks great. What method are you using to get the "width" panels perpendicular to the side panels? I created right angle jigs with two sheets of plywood, but they are no perfectly 90 degrees.

Also, let me know if you ever plan to sell the lab12 drivers...I need another one for the second Tuba60 I will build later this year..

Thanks for the compliments. I cut as much as I can on the table saw with known square edges against the fence. I also used a homemade crosscut sled for some of the cuts. On the large panels that are too big for the table saw, I use a cheap track saw that I got off Amazon years ago.

I use a lot of plywood scraps to keep the panels perpendicular once they're in place. I'll measure the distance between the panels at the bottom (the side panel where all the layout lines are drawn) and use a plywood scrap at the top making sure the measurements stay the same between the top and bottom of the panel. Also be careful when installing braces because it's easy to make the panels get wonky if you wedge them in too far or not enough.

You can see my plywood scraps here keeping panels square:
Screenshot 2026-03-10 at 7.42.42 AM.png

That's helpful information. I realize now that the plan images did show some scrap pieces for alignment. I suppose the challenge is to get the very first panel perpendicular..

[shawn_g]

That's helpful information. I realize now that the plan images did show some scrap pieces for alignment. I suppose the challenge is to get the very first panel perpendicular..

If you follow the plans closely, I'm sure it'll come together just fine! Bill's designs are all pretty forgiving and yes it does make it easier if everything is square and perpendicular, but small mistakes are easily correctable even after the PL has dried.