THTLP build --- veneering

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DaveMacKay
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Joined: Tue Aug 03, 2021 3:10 pm

THTLP build --- veneering

#1 Post by DaveMacKay »

@Seth encouraged me to post some photos and info about the THTLP build that I am working on. Here goes ...

I am planning to build two powered THTLPs. Each THTLP will be built with a Dayton RSS315 HF-4 12" woofer and a Dayton SPA250DSP plate amplifier. I have the woofers, but the amps are on backorder and won't arrive until the new year.

I'm building the first one now; the second one may have to wait until spring when the weather warms up. The builds rely on PL Premium construction adhesive which is only rated for use in temperatures above -7 degrees C (19 degrees F). Because I live in Canada and work in an unheated garage, I'm racing to finish the first build before the temperature gets too cold.
Garage workshop.JPG
Also, my wife wants my tools out and her car back in the garage before the snow comes!

Progress to date
Here's what I've done so far, pretty much on a day-by-day accounting:

1) I picked up two 4' x 8' sheets of 1/2" Baltic birch plywood. The plywood was expensive --- CAD$160 (roughly US$125) per sheet. Because I don't have a truck, I had the lumber yard cut each sheet into:
  • 1 x 18.5" x 72"
  • 2 x 14.5" x 72"
  • 1 x 24" x 48"
so that I could fit the material in my Mazda3.

2) I used scrap lumber that I had laying around to build a number of jigs from the plans that Bill makes available. They've been invaluable. If asked, I would recommend making more of the panel jigs and circular saw sleds so that some could be dedicated to the different angle cuts that must be made.

Bill's didn't provide plans for a circle cutting jig, but I built one based on some I'd seen on YouTube.
circle cutting jig.JPG
3) I cut the front and back sides and marked out the lines for all of the panels.

4) I cut out and installed panels 1 and 2. I fastened the panels with brads and some strapping to hold them while the PL Premium cured.

5) I cleaned up the PL Premium squeeze out from the previous day with a sharp knife and a scraper. Then I cut panels 3 and 4 and installed them using PL Premium and brads.

6) I cleaned up the PL Premium squeeze out from the previous day. Then I cut panels 5 and 6. I installed panel 5 and then cut the hole for the woofer in panel 6. There's not much room for error; I cut the hole about 1/8" larger (in radius) than the inner diameter of the driver mounting gasket. Even that little bit of space may have been too much; the mounting screws are showing through the sides (shown circled in this photo).
screws close to edge of hole.jpg
I hoped that the mounting blocks would be sufficient to hold the screws and salvage the panel, but I was concerned that there was insufficient support for mounting the woofer.

7) While i was sorting out what to do about panel 6, I ran a test on the woofer (in the soon-to-be replaced panel 6) to ensure that there wasn't any interference between the woofer and panel 6. After that I ran the woofer for 12 hours for burn-in. Here's my setup:
woofer test setup.JPG
I'm using a signal generator to send a 1 Vpp 30 Hz sine wave to an AV amp via a BNC-to-RCA cable. The amp is connected to the woofer with speaker wire. I stripped enough insulation off the speaker wire so that I could connect my DMM. I turned up the volume on the amp until the DMM showed 10Vpp (RMS) at the woofer. I let that run for 12 hours.

After asking a couple of questions on the forum (thanks!), I resigned myself to having to make panel 6 all over again. I wasn't ready to face that, so I moved on to other things.

Because my THTLP will only be 15" wide, I only needed one of each brace. I made them all at once.
Braces.jpg
I also rough cut the remaining panels (panels 6-10).
rough cut panels.JPG
I'll cut them to their final dimensions as I go about installing them .

Current status
I figure that I'm about 1/3 of the way through the build. There's not much to see at this point; the photo shows the THTLP with one side and panels 1-5 installed:
THTLP so far.JPG
Hopefully, I'll get some panels 7 and 8 (and maybe 9 and 10) cut and installed tomorrow. I'm a bit gun-shy about re-cutting panel 6, so that I may do that last (even though it's out of the order of Bill's instructions).

I'd like to give a shout-out to @TomSmit, who has been very helpful. Originally I had planned to have Tom build the THTLPs. But, because I had some time and needed a project, and Tom's schedule was busy, I thought I'd try the build.
Last edited by DaveMacKay on Mon Jun 27, 2022 10:19 pm, edited 5 times in total.

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Seth
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Re: THTLP build in progress

#2 Post by Seth »

Wow Dave! Great writeup :thumbsup: And good for you, taking it on yourself!

I find that when I'm building my cabs, I get in different moods. Sometimes it's a meticulous perfectionist mood. And sometimes it's a F#*@ it, let's just get it done, mood.

I really can't say which direction I'd take with the baffle if it were me. It would depend on my mood. But, re-doing the baffle IS absolutely the right thing to do.

Yes, there's concern for the holding power of the screws, but there's also the added potential for leaks through the screw holes in the driver flange being uncovered, even on locations that didn't breakout. Could they be reliably sealed up? Maybe. Quite possibly, even. But, the right thing to do is remake the part. I commend you on that choice.
screws close to edge of hole.jpg
When you don't have to put the basket in the cutout (like your situation), you can intentionally size and make the hole a bit smaller (say 1/16" radius,1/8" diameter smaller hole than the driver gasket ID) to give you a little more meat there for the screws, then sand down and soften the edge on the driver side of the baffle to give you clearance for the surround if needed.

A note on the plywood; 5x5 sheets seem to always be the better deal, by a good margin. I know the prices have shot up and I haven't priced it recently. But here in California, a year or two ago, a 5x5 sheet of ½" BB was about $36 (± $1.40/ft²) and a 4x8 sheet of the same stuff was in the $90 range (± $2.81/ft²), twice the cost per SqFt.

Also, if you need to, a plug in space heater will probably keep the garage warm enough for the PL (although maybe not warm enough for you. LOL (I see your lack of insulation :) )). If your electricity cost is $0.15/kWh, a 1200 watt space heater will cost about $4.32 per 24hours of run time. Handy if you need it. Put a bowl of water in front of the heater too. PL is cured with moisture. Dry air = S L O W cure. At the lower limit of the PL specified temperature range, I suspect it's the limited amount of moisture air can carry/hold below that temperature that makes it not reliably cure at lower temps, not necessarily the temperature itself. Just a hunch though. Don't take that as fact.

Anyway, thanks for the awesome writeup Dave! What a great evening read :thumbsup:
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

ACUA
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Re: THTLP build in progress

#3 Post by ACUA »

I have always put a heavy bead of weather caulking around my drivers and blob each screw to assist sealing and ensuring the screws do not back out. This seems to aid in sealing and adhesion but makes it a lot harder should you ever want to remove the driver for any reason.
Advanced Concepts Underground Audio

Bruce Weldy
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Re: THTLP build in progress

#4 Post by Bruce Weldy »

DaveMacKay wrote: Thu Dec 16, 2021 12:31 am
Also, my wife wants my tools out and her car back in the garage before the snow comes!
35 years ago, we moved into our house. 34 years ago, my wife had to leave her vehicle out of the garage while I did a project.....it hasn't been back in there since. And it's a large two-car garage.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Bill Fitzmaurice
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Re: THTLP build in progress

#5 Post by Bill Fitzmaurice »

I used my garage as my shop for three years, ended up building a shed workshop in the back yard when the garage wasn't big enough anymore.

tallevan
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Re: THTLP build in progress

#6 Post by tallevan »

Regarding not having enough inside edge for the driver mounting screws in the baffle, I recall in one of the plans (at least) Bill suggesting making the driver opening somewhat conical.
Probably easier to see a picture, but I cut the driver hole with a jigsaw with the blade at an angle of around 25 degrees.
Then the driver mounts on the side of the baffle with the larger hole.

howiez
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Re: THTLP build in progress

#7 Post by howiez »

Beautiful!
I'm going to enjoy this build thread for sure.

I love the Dayton RSS drivers, and I have that same amp in my THT, I love it.

I would agree with Seth, get some heat and moisture in there. I've been schlepping my DR's down into the basement every night after I heat the garage all day while working on them.

Bruce Weldy
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Re: THTLP build in progress

#8 Post by Bruce Weldy »

Or, you can all just move to Texas where none of this is a problem. :mrgreen: :cowboy:

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Seth
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Re: THTLP build in progress

#9 Post by Seth »

howiez wrote: Thu Dec 16, 2021 1:01 pm I've been schlepping my DR's down into the basement every night after I heat the garage all day while working on them.
If I were in your shoes, I'd be real tempted to create a quick little lift off "greenhouse", framed with 1x2 and double layer of visqueen (double pane) to put over the project and put a little heater under too (a 100 watt incandescent light bulb might even do).
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Tom Smit
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Re: THTLP build in progress

#10 Post by Tom Smit »

Dave, I can relate in regards about the baffle. However, if one leaves the baffle as is, it will always bug one whether it will be good enough for the coming years/for really letting the cab pound. Some meticulous setting up of the router jig, using scraps for testing, will result in a near-perfect cut out.
TomS

DaveMacKay
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Re: THTLP build in progress

#11 Post by DaveMacKay »

Thanks for all of the comments and suggestions!

Today's weather was unseasonably warm, so that I wanted to make good headway on the THTLP build. I made some progress but was slowed down by one error that I had to fix, and by the need to let the PL Premium cure on some panels before affixing others to them.

I started by cutting panels 7 and 8, which were a bit tricky since they need to be cut at a 9 degree angle, and because they are a bit large for my table saw. But that went smoothly. Since I had already cut the braces, I moved on to install panel 7.

It should have been simple. But it wasn't.

The instructions said only "Cut and install panel 7 and the 1/7 and 7/4 braces". I installed the panel easily enough but installing the braces was a mess. I tried running a bead of PL Premium on them and sliding them in place. All that did was make a sticky mess all over. I couldn't get the braces in the right position, let alone level. Getting one brace in place would throw off the other.

It was obvious that I wasn't going to be successful with that approach, so I took out the braces and panel 7 and cleaned off all of the PL Premium. It took a scraper, some Varsol, and a lot of shop towels, but I was able to get both the panel and the braces clean.

I decided to try attaching the braces to the panel ahead of time, and then installing that assembly as a unit. That worked OK for panel 7.
panel 7 and braces.JPG
With that success behind me, I fastened the brace (and cross-brace) to panel 8
panel 8 and brace ready too.JPG
I wanted to let the adhesive dry on panel 7 before trying to attach panel 8 to it, so I'll install the panel 8 assembly tomorrow.

I also attached the brace to panel 9, but I won't install it until after I've made a new (better) woofer baffle (panel 6), since it would be hard to install the baffle with panel 9 in place.
panel 9 with brace ready to go.JPG
Although I've cut panel 6 to size, I haven't yet routed out the hole for the woofer. I'll try again with my router and the circle cutting jig I made for it.
circle cutting jig and rough panels.JPG
Wish me luck!

The next milestones I'm aiming for are:
  • installing panel 8
  • cutting a new woofer baffle, and installing it (with brace and speaker retention blocks)
  • installing panel 9
  • cutting and installing panel 10
There'll still be work to do after that, but I'll feel that I'm on the home stretch.

(By the way, some of the photos I post are rotated from their normal orientation. Is there a way to adjust them when adding them to a post?)

howiez
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Re: THTLP build in progress

#12 Post by howiez »

Seth wrote: Thu Dec 16, 2021 4:56 pm If I were in your shoes, I'd be real tempted to create a quick little lift off "greenhouse", framed with 1x2 and double layer of visqueen (double pane) to put over the project and put a little heater under too (a 100 watt incandescent light bulb might even do).
Thats a great idea! I've actually been shopping for a used natural gas furnace to put out there so I can heat all the time, at least keep it at 60ish. My house furnace is on the other side of the wall so gas is close.

howiez
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Location: Fox Valley, Wisconsin

Re: THTLP build in progress

#13 Post by howiez »

DaveMacKay wrote: Fri Dec 17, 2021 12:27 am Thanks for all of the comments and suggestions!

I decided to try attaching the braces to the panel ahead of time, and then installing that assembly as a unit. That worked OK for panel 7.
panel 7 and braces.JPG
Looks great so far Dave!
For sure we all make mistakes and it sets us back a bit, but we learn!

As for the braces, I struggled with those too, very messy when you slide them in. Amazing how slippery PL is until its' on your fingers, then it's the opposite!

What I finally did when building my THT, was loosely clamp the panel in place, dry. Then dry fit the braces and mark a line at whichever end is most accessible (or both if possible). Then I take it all out and glue them ahead of time. you can put a temp cleat and wax paper as a stopper while it cures. Or if you have a nail gun, you can pin them all, and go right to the panel glue phase. It helps stabilze the panel as you glue it in, I found this much easier. You still get a smear on the open size of the braces, but nowhere near as bad. And like they all recommend here, you let them cure an hour or two, and scrape the excess bead off and you'll get a nice little squeeze out fillet of PL when it finishes expanding.

Keep up the good work!

DaveMacKay
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Re: THTLP build in progress

#14 Post by DaveMacKay »

I made good progress on my THTLP build today.

1) I cleaned up all the squeeze-out on panel 7, and applied caulking to all joints --- just in case --- so that everything will be air tight.

2) I installed panel 8 and its brace and cross brace.
  • Panel 8 was a bit warped so that the joint between panels 7 and 8 didn't line up perfectly. I was able to force a reasonable fit using a temporary brace to pull the two panels together.
  • The cross brace wanted to warp so I put a clamp on it to pull it back to square.
panel 8 installed.JPG
3) I cut another baffle for the woofer (panel 6). This one should be OK.
  • I changed the radius I was using on my circle cutting jig by a tiny, tiny amount --- likely less than the diameter of the finishing nail I was using as a pivot. That resulted in a slightly smaller circle which meant a closer fit to the woofer and more room for the screws.
  • I used #8 screws to mount the woofer to the baffle instead of the #10 screws I used the last time. I think that the tolerances are so tight that using the smaller diameter screws made a great deal of difference.
Baffle 2.JPG
The cut-out isn't perfect, there is a small section that is gouged in. That happened because, when I fastened panel to my work surface, before attaching the circle cutting jig, I only fastened it inside the circle to be cut out. I should have fastened it there and in the area that will form the baffle (i.e., outside the circle) too. Because I didn't, when I took my last pass with the router, the circle was cut free and the rest of the panel moved into the router bit. Fortunately, that mistake seems to be of no consequence.
circle cutting jig.JPG
My home-made circle-cutting jig worked, but was a pain to use: it was hard to mount it on the pivot point (a finishing nail drive into panel 6) and it was hard to make tiny adjustments. I've ordered a commercial circle cutting jig. Although it'll be too late to use on this project, I'll have it when the time comes to build my second THTLP.

4) I added the speaker retention blocks to the new baffle.
with retention blocks.JPG
5) I cut panel 10. I decided to wait until the PL Premium on panel 8 had cured before installing it.

The warm spell we've been enjoying has passed. The temperature is now below freezing which will affect how the PL Premium cures. But the finish line is in sight.

Tomorrow, after cleaning up the PL Premium squeeze out and caulking the joints (admittedly a "belt and suspenders" approach), I hope to:
  • mount the woofer in the baffle and ensure that there is no interference between the woofer and the baffle
  • install panel 6 (the speaker baffle) and its brace
  • install panel 10
I'll probably wait for the next day (so that the PL Premium will have cured) before installing panel 9 and the last side of the subwoofer.

howiez
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Location: Fox Valley, Wisconsin

Re: THTLP build in progress

#15 Post by howiez »

Looking great!
If I remember correctly , I struggled with cutout diameter on my THT and the Dayton RSS390. I used T-nuts, epoxied them in, and put two short screws, also epoxied on the T-nut flange to help retain. The T-nut flanges were in the bore of the cutout all the way around. I feel like that giant surround on the Dayton makes the cutout hole large, and the bolt circle isn't much larger. They probably do much better with a front mount, but rear is what we need here, so we struggle!

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