OTop12 Build Thread

[Grant Bunter]

All your piezo cutting work is spot on

[miked]

Thanks, Grant! I really took my time with the piezos; as much for safety as I didn't want to screw them up b/c I only had three spare tweets (now two, as I did screw one up). Now I just hope the glue up process goes well.

Along those lines:

What exactly is the process for gluing them up? I bought the PVC glue/cement that Leland sells...Oatey brand something. Does this glue have a "tack time" like 3M spray adhesive? Do you put glue on both surfaces and then hold them together for a second? A minute? How many can you glue up at once? See what I'm getting at?

I do plan on coating both sides of the joint with glue. It will add strength and nobody will see the glue anyway as I'll be going with blacked-out grills.

Oh and before I really screw things up; wax paper WILL prevent the array from sticking to the jig AND to the wax paper, correct?

Thanks for all your advice, everyone, and thanks for looking. More tonight.

[Michael Ewald Hansen]

Thanks, Grant! I really took my time with the piezos; as much for safety as I didn't want to screw them up b/c I only had three spare tweets (now two, as I did screw one up). Now I just hope the glue up process goes well.

Along those lines:

What exactly is the process for gluing them up? I bought the PVC glue/cement that Leland sells...Oatey brand something. Does this glue have a "tack time" like 3M spray adhesive? Do you put glue on both surfaces and then hold them together for a second? A minute? How many can you glue up at once? See what I'm getting at?

I do plan on coating both sides of the joint with glue. It will add strength and nobody will see the glue anyway as I'll be going with blacked-out grills.

Oh and before I really screw things up; wax paper WILL prevent the array from sticking to the jig AND to the wax paper, correct?

Thanks for all your advice, everyone, and thanks for looking. More tonight.

Yes, wax paper is a must..

Use modelplane glue or similar fast curing super glue to 'pre-glue' the tweeters.. Once they are glued with that, you can use the Cement.. Careful not to put too much on as it melts the plastic a little bit for the bond (doesnt look pretty if you put on a huge amount and the tweeters all look melted..

[miked]

Thanks for the super-glue tip, Michael. I know just the stuff to use, too. Loctite Control super glue. Basically, it's thicker viscosity superglue in a squeeze bottle with a narrow nozzle. Perfect for this application.

And I had no idea that the cement actually melts the plastic a little. I had every intention of slathering the stuff on, too. I guess a little will go a long way in this case?

[Michael Ewald Hansen]

Thanks for the super-glue tip, Michael. I know just the stuff to use, too. Loctite Control super glue. Basically, it's thicker viscosity superglue in a squeeze bottle with a narrow nozzle. Perfect for this application.

And I had no idea that the cement actually melts the plastic a little. I had every intention of slathering the stuff on, too. I guess a little will go a long way in this case?

Just a few dabs of the super glue to hold the tweeters together and then use the cement when the whole array is glued with superglue - atleast thats what i do.. The fumes from this stuff is pretty harsh, so use it in a well ventilated room or outside. Try gluing some of the cutoffs from the tweeters together and get a feel for how it works..

[Rune Bivrin]

Model plane glue is not the same as super glue.

Model plane glue is essentially plastic dissolved in a solvent such as toulene, xylene or acetone. As a matter of fact, acetone alone works quite well as a glue for a lot of plastic. Just wet the surfaces with acetone and align the pieces. After that a mild pressure for a few seconds and it's complete.

[AntonZ]

I don't use superglue, just the "melding glue" or cement. No "tack time", bring them together while the glue is still wet. The solvent makes it dry rather quickly. Personally I have done just a few at a time, let it set and cure for a while, then add one or two more elements, and so on until the array is the desired length. I did not do the entire array in one go. Guys like Leland who have build hundreds of arrays will probably move faster.

After initial glueing the arrays are still rather fragile. So I have done several passes of "add a bit more glue/cement to either side", place back on the jig and let it dry.

Wax paper at all times indeed. The cement/glue does not stick to wax paper. +1 on plenty ventilation or working outside.

[miked]

Thanks for all the tips, everyone. I plan on giving the array joints multiple coats of glue. I'm not concerned about the appearance of it as it will be hidden by the grill. Just don't want any tweets snapping off as time goes by.

I will most probably just stick with the ABS cement, this stuff:


Only thing I'm curious about at this point is the setup time for the glue. I plan on letting the array sit overnight before trying to pick it up or move it. But I guess after a minute or so I can continue gluing more tweeters to the assembly?

[miked]

I received an email reply from the Duratex folks; such a fast response! Very refreshing in this day and age.

Here is my exact question to them:

Hello. What product do you recommend for patching screw holes and other dings in a plywood speaker box before applying Duratex? I was planning on using Bondo, but have been told that it outgasses and would ruin the Duratex finish. Thanks for your time.

And their reply:

Regular interior wall spackle is what we recommend.

I'd say that's pretty cut and dried. I'll be returning the Bondo to Lowes. Don't have my receipt, but I'll take a store credit for a big old container of Spackle...I'm going to need it. Note that he did NOT specifically say "Don't use Bondo." Maybe they own stock in the Spackle company too? Who knows. But, I'll go w/the Spackle.

[miked]

Just so you don't think I'm loony for "wasting wood" and trashing my back panels:

Old and new panels in cabs, side by side. Both panels have been pushed to the upper right as far as they will go to highlight how short the old panels are...and how badly my cabs are out of square.


Old panel closeup (didn't move anything)


New panel closeup


Once I center the new panels I'll have maybe 1/16" all around which is fine by me. A LOT better than 5/8". BTW, the new panels are exactly 20 7/8" x 14.0". Now to cut up the old backs and get my rear panel braces out of them. And cut new recesses for the cabinet-mount Speakons pictured above AND drill new mounting holes. That'll take the better part of the evening. More pics later. Maybe I'll start the tweet glue up, but I doubt there'll be time tonight.

[ncgrove]

I imagine your old panels don't look so bad if you center them. The gap isn't the end of the world. They'll still be air tight, which is sufficient. You'll never be able to see the gap in the back panels if you paint everything black.

[miked]

I imagine your old panels don't look so bad if you center them. The gap isn't the end of the world. They'll still be air tight, which is sufficient. You'll never be able to see the gap in the back panels if you paint everything black.

Trust me, they weren't usable. Notice that I'd already cut all screw holes to mount the panel. They were all placed at the 1/2" mark. Combine that with the panels being so short all around and no way would half the screws even make it into the panel mounting strips. I don't want to compromise at all and I had 1.5 extra sheets of BB left, so I cut new panels.

Here's what's left of the old ones. I cut the "wings" off to use for the rear panel braces for the new panels. Reuse, recycle, right? Wonder what I can do w/these things? Seems a shame to throw'em out.

[miked]

Finally have gotten around to gluing up the arrays and so far...it's easy. I know that is b/c:
A. All my piezos are cut well b/c I used the jig
AND
B. I'm using the melded array gluing jig from the plans and a straight jig I made myself. The key phrase here is "I'm using the jigs." I can't imagine even trying to do this without them. And man, that Oatey cement...my head is a bit loopy ATM.

So how long are you supposed to let the array dry before you move it? The cement seems to dry very quickly, but I'm not touching it until it's time...and that would be when you tell me it is time.

Pics or no array, right?

Straight array. After gluing them up edge-to-edge, I glopped-on a line of cement across each joining point.



Slightly diff angle


Nice and flat. I don't care about the glopped on glue b/c the arrays will be behind a blacked-out grill


Melded arrays. I am gluing up one side at a time...*shrug*...it seemed easier to me this way. Glue up left side, then right side, then sides together.



I built my melded array jig 28" long so I could glue up two arrays simultaneously...but it worked out this way that I could glue up the sides separately. Works for me, I guess.


Both jigs on the workbench, arrays drying (curing?)


BTW: I found out that (so far) I've only had to rotate the elements to get the tweets to butt square up to each other on the straight array. No idea why that is. On the melded the elements are not rotated, but they do indeed butt up even and square. Wiring will be a PITA no matter which way they face, so I figured just leave them be as-is.

And last but not least, the new backs I cut, with the recesses for the cab-mount Speakons done and the backing plates glued/nailed in. You'll note a "#1" on the back. I have each back hand-fitted to it's matching cab. You can see the new rear panel braces too. They aren't 100% identical and I'm not worried about it. They are all 11"x3" and that's what matters.



I may continue with the arrays later, depending on how soon I can move them. If not, that's what tomorrow is for. Thanks for reading.

[miked]

I just flipped the arrays over and glopped a coat on the front joints. How many coats of cement are you supposed to put on? If the cement actually melts the plastic together, when you put a second coat of cement on, doens't it melt the first coat? Heh, n00bs and their silly questions, right?

[miked]

I'd be a lot further along than I am. Nonetheless, made progress tonight.

Finished drilling the recessed Speakon mounts; I'm very happy with these. Going to look great once the cab is Duratexed. The recess is 2-1/8" and the through hole is 15/16" for anyone who's interested in knowing.







Attached the rear panel braces.


I still need to predrill the mounting holes for the rear panel, but I wanted to get the final "construction steps" out of the way. I"ll do that tomorrow. Am pondering 6 screws across and 5 up vs. 5 and 4. I've seen some OTops with like 30 screws on the back...I think that's overkill but I'm wondering where the happy medium is? These cabs are vented...it's not like there's a ton of pressure inside like in a Titan or Tuba.

Continued with the arrays. The straight arrays are done. Three coats of cement front and back and they're good. Just started joining the melded arrays together tonight. I glued up the left and right sides last night, now I'm gluing the two sides together. This step was not as easy as all the previous steps. In a couple of spots the two halves don't meet up perfectly; got a couple of 1/16" gaps. Glued them together, waited about 15 mins, then globbed on a coat to try and fill the cracks. Didn't get all of them, but I"ll do that tomorrow morning before leaving for work. Tomorrow night, I'll flip them over and get to cementing the fronts.

Straight arrays and left/right halves before glueup tonight.



Melded on their first round of cement.





So what's left, you ask?

Finish arrays (done tomorrow)
Cut and mount grill mounts
Decide if I'm going to try to mount top hats or not...still undecided.
Line cabs with mattress topper
Attach backs w/a few screws and finish up with flush-trim bits
Spray paint mouths black (not spraying the whole cab with primer first, just the mouths since they're not getting Duratexed.)
Spray paint thru port holes.
Solder up crossovers
Spackle the nail holes, gouges, oopses and everything else
Roundover the corners.
Duratex the cabs.

So many steps/things...I hope I don't skip anything accidentally. Then to attach and wire up the drivers, arrays, crossovers, attach the back put on the corners and feet and grill and *whew*, I need a beer, now! I figure another 3-5 days, minimum, though we'll see how much I get done this weekend. I hope to at least be ready to Duratex by Monday.

More tomorrow.