BillFitzmaurice.info

I built a T18 a year ago powered by a Tang W6 6.5" sub. I got the sub on clearance for cheap. I did a search on the forum and it appears it will work in a T18, but the output will be diminished due to the lower Vas, which is less than the required Vas per the plans. The rest of the specs are good. The box was built as narrow as possible, so 8.5"
The box finished out well, I used the ExoHyde coating which is super easy to apply and is tough. I like this product. It is almost a gel out of the can. No drips, no smell, dries in minutes for recoat. Super easy cleanup with water, if you are quick, it will even wash off your hands.


The output with the W6 was much lower than expected. I had to drive this box pretty close to the limits of the W6 (50 watts) to get any output from it. Definitely a fail compared to my other T18 with the Dayton DCS-205-4 8".

A year goes by, I got tired of looking at this failed box. With the price of 1/2" plywood over $60 now, I decided to try to fix this by taking it apart, widening it, and installing a DCS-205-4 8". I figure this "rebuild" will help anyone that messed up their box, and it didn't perform as expected.

Rebuild process.

I had a 5.5" strip of 1/2" plywood by 8' long left over from this build. Its been sitting on my porch for a year.

1. So, I am going to split this box in half.
2. Then add add the 5.5" strip back in to make the box 13.5" wide.
3. Recut the speaker opening.
4. Add braces. My original box did not have any braces except the opening, since it was only 8.5" wide.
5. Refinish the spliced pieces and box touch up.
6. Install the DCS-205-4

First thing was to split the box in half, almost. I did have one brace on the opening, so I made sure the table saw blade missed it by offsetting the fence so I just missed the brace. So one half box was 4" wide, the other 4.5" wide. Since my table saw blade will only raise about 4", I cut all 4 sides of the box, then used a big handsaw to complete the cut. The handsaw is skinnier than the table saw blade, so after the box was split apart. I used a straight edge and a Japanese finish hand saw to cut the inside edges to match the outside edges that were cut with the table saw. Then I planed the edges with some 80 grit sandpaper glued to a 3/4" of melamine to get the edges flat.

Next step was to fill the old 6" diam. half hole, where the W6 was mounted. What I did not want to do is try to cut the 7.1" diam. hole for the DCS-205-4 inside the box. I traces the opening of the 6" diam. semicircle onto a piece of plywood. Then cut it out, then placed it in the box, so I could trace the new speaker opening. I then cut out panel 2, out of the 5.5" strip, and held it in place where it would go. Then traced a 7.1" diameter compass to scribe panel #2 and the semi-circle plug. I then cut out the new opening on the plug, and panel 2 (which became panels 2A and 2B). Once I had the plug scribed. I cut out the new speaker opening. Then I duplicated this piece for the top side of the box. I then glued this piece into the box halves. So, this was a win in the fact, that I could cut the opening in the pieces and not have to try to cut out the opening inside the box.

So decisions have to be made. I could widen this box two ways.

1. I extend the 5.5" width pieces on one side, starting from panels 2A, 2B, 3... to section 12. Then the braces. Just like you build the box in the plans. Then when those dry, I just glue the other 4" half of the box onto the top.

2. Or I extend just the 5.5" wide sections 2A, 2B, 3, 4, and 5. Then glue the 4" half of the box to that, then continue panels 6, through 12 and all the braces.

Well I did option #2, just because when I glued in 2A, 2B, 3, and 4; I could already see that I was going to have some alignment issues with some warpage. By the time I completed all of the 5.5" sections these were not going to mate perfectly with the 4" half box. The most import panels are the panels 5 and 6 pieces and joints. If these are not air tight, you will not know it since you can't see them from the outside of the box or inside of the speaker chamber.

I glued 2A, 2B, 3, and 4 then the top 4" half of the box. Then let them dry. Then touched up the joints with more PL3. There were some gaps. Then I glued panel 5. I used a ton ofPL3.
Remember my panel 2- the 5.5" wide expansion piece is now two pieces (2A and 2B) since the speaker 7" diam. cut out goes all the way through. So Panel 2 is now really in four pieces. The two half moon slivers, then the two 5.5" wide expansion pieces. I could see that these were not completely lined up perfect inside the chamber. More on that later.

So, panels 6 through 12 are just glued in the same order as the plans and the corresponding brace is added. Care was needed to try to get the 5.5" expansion piece lined up as best as possible.

So all the panels are glued and braces in. I made another brace to match the existing large exposed brace on panel 12/7.
Now here is the problem, with Panel 2 now four separate pieces glued together, but not at the same time there is some misalignment, but not horrible.
I was able to use my Japanese flush cut saw to smooth it out until it was all one plane with no steps. The hole is approximately what I need 7.1" diam. I used my sanding board to smooth the dried PL3 so it would take a gasket well.

Now, on to the refinish. I filled in all gaps with PL3 on the outside and sanded it down. The plywood is pretty rough, it was when I built it originally. The ExoHyde covers pretty well.
With one touch up coat, it wasn't too bad. I wasn't worried too much about cosmetics, since this will find home in my trunk.
With two coats completed.

Now, to fit the DCS 205-4 driver.

You may have already guessed that this would be the Achilles heal for the project. Without having a full panel 2 out of the box, where I could fit the driver centered over the hole and predrill the holes, installing the speaker was going to be tough inside the finished box.

I did my best to center the driver over the hole. I knew the hole was big enough, because I measured it. I then set in a few 1" sheet rock screws in by hand using a stubby phillips screw driver. I then put in the rest of the screws. It was not easy, since these were not predrilled, but I used no blocks, so I only had to go the 1/2". Sheet rock screws are sharp so they start easy. The last screw in back never tightened, all the way. Not a good sign . So the speaker is not centered. Rats....

At this point since all the screws are in and hard to get the screws in or out, I did the air test using at 30 Hz and a 25 Hz tone. Definitely some air leakage in the back, but no cone rubbing. I looked through my supplies to see what I had. I had a tube of latex caulk that was old. It was pretty thick, wouldn't come out the end with a caulk gun, but it wasn't cured. I cut the tube and squeezed out a bit and was able to roll it and make a rope caulk. I made two 12" long by 1/4" ropes, and used that to seal the speaker around the perimeter. I still had some air leakage, but I could tell it was through a few screws, so they must have busted through but not sealed. I put a few pieces of rope caulk over those. Tested again. No leaks!

I sealed up the access door and now the moment of truth, listening.
The speaker was not broken in at all, and the caulk wasn't fully cured, but I set the T18 on top of my TT and let her rip at 1/4 power.

This sounded great. I am really impressed that this 13.5" T18 has almost the output of my TT using the same driver. The finish is acceptable. Up close you can tell there is a 5.5" strip going around the box, but the ExoHyde hides it pretty well. A few more coats of the ExoHyde and you would probably never see that the box was grafted together.

So the W6 T18 is a loss, but the repair was a win. This only cost me a tube of PL3 and some time. I guess that it probably took a little over half the time of just building a new box from scratch, but the satisfaction of fixing something, is priceless. I also only had to use my table saw for 5 minutes. The 5.5" strips I could cut with my chop saw.

One of the most amazing and gutsy feats I've witnessed in speaker building. Well done. Thanks for sharing the win. I completely enjoyed the story.

Wow! That was an adventure, and I love it. It basically only cost you some time, no parts. Kudos.

Good stuff, yes thanks for the detailed write up.

What a feat to even attempt!

Great job.

It's similar to when I was in college and built a Jensen Imperial folded horn, made wider to take three fifteens. Made of 1" particle board 'The Hulk' came in at 300 pounds. We eventually tired of needing four of us to lift it into the band van, so we cut it down the middle to create two 1x15s. I don't remember exactly how we did it, but I suspect we used a circular saw to go around it first and then used a handsaw to reach the inner plates.