OTop12 Build Thread

[miked]

Outside in the trailer? That would be 150F+ inside the trailer in the Jul-Sep timeframe. If they've not come off yet, they never will. I'll be going the 3M spray method then. Thanks.

I have YARDS of black grill cloth that I bought from PE probably 10 years ago...can't figure a way to make it work with a metal grill. I'm sure a few hours of tedious sewing would secure the fabric to the grill, but the sharp edge of the grill material will make short work of the cloth. Oh well.

You can get the AC foam at Walmart. It's a perfect fit for the OT12s, just trim a little off. No splicing.

Yepper. Dirt cheap too. And that's good; it's AMAZING how fast the incidental costs for these cabs add up. Screws/hardware/jacks/wires/wood putty/spray paint...cha-ching!

[miked]

Well, I just got back from a marathon horn panel trimming and sanding session. My "dead square cabs" aren't. One is almost perfect, one needs work and the other two need a lot of work. I'm feeling pretty humbled right now. Suffice to say that I've discovered that if your horn panels are off AND the top isn't dead square w/the bottom, you're in for a lot of additional work. What pisses me off the most is that I really didn't see this coming. You learn SO MUCH from your first BFM cab build, that's for sure.

I could only trim so much w/the circular saw/sled or risk cutting into the top/bottom. I have a belt sander with a 60-grit belt on it and it made short work of leveling the horn panels w/the top/bottom, but the outer edge still shows proud. Once the sides are on, a top-bearing flush trim bit will fix that.

The good news is that it's all fixable. The bad news is that over the next few days I'm going to become VERY familiar with the following tools:

Clamps
Flush cut trim bits, both top and bottom bearing
PL
Clamps
PL
Sandpaper
Clamps
RO Sander
Clamps
And if all else fails, The BFH.

And to add insult to injury, even though my back panels and their braces are dead-on matches for the plans, the braces hit the magnet on the jumbo Delta Pro drivers. I will basically have to hollow-out both braces where they "surround" the magnet AND cut them about 1/2" shorter to boot. Instead of doing all the hollowing out, I will probably just cut them about 3/4" shorter somehow. Maybe buy one of those "Japanese flush cut saws." OR, maybe I'll just "squish them down" with the belt sander.

If I was using Neo drivers, this wouldn't be an issue. I've had these drivers over a year so returning them isn't an option and aside from that, I do not have $800+ for four Neo drivers. I will use what I have.

IMO, I just added at least 3 days to this build; keep in mind during the week I have just a few hours per evening to work on them. It's not the end of the world, but with as careful as I've been, this was really shocking. I'm not working on them any more tonight...too ticked right now.

[Jon Barnhardt]

That happens to all of us. Just when you think you are almost finished, something goes awry.

That's why the belt/edge sander is one of the most used tools in the shop!

[Grant Bunter]

Yep, everything keeps on adding up, just remember it's still cheaper (and better) when you're done than walking out door with a significant chunk of cash to buy what someone else built.

I had my share of troubles building my tops as well. In the end they worked out fine!
You did the right thing, walking away is a good thing sometimes.

Tomorrow's another day

[miked]

Thanks for the confidence boost, guys. Walking away was highly preferred to smashing them to bits which did cross my mind for a second.

Basically, on three of the cabs the top is slightly twisted in relation to the bottom, which also makes the horn panels twisted. So now the sides don't line up by roughly 1/4" in most spots and I think 5/8" in one or two spots.. I've managed to cut the horn panels even with the front of the cab, but b/c of the "twist" b/t top and bottom the sides don't fit anywhere NEAR square. I know on larger panels on bigger boxes like Titans and Tubas, you can really crank down on the clamps to force panels into alignment, then glue and clamp.

But on smaller boxes like this, I'm not sure how much torque I can/should apply in forcing the sides on. I'd hate to tear the baffle or horn panels or torque the baffle out of alignment and then the driver doesn't seat correctly. I guess I'm going to find out, right?

I'm thinking I SHOULD be able to get the box closed up and then just use flush trim bits/bondo/copious amounts of Duratex to hide the boo-boos as best as I can. Worst case scenario is that I have to cut 8 new sides which would be a PITA as my wimpy drill press took FOREVER to cut the handle holes with a 1.5" Forstner bit.

And I thought by tonight I'd be spraying the primer on. Sheesh.

[miked]

When you think you have enough clamps, you realize that you do not, in fact, have enough clamps. I have plenty of small (under 18") clamps. I need many 24" clamps for this next phase of the build process; I have 6 clamps that size.

So I finally figured out a clamping strategy that will enable me to get the sides on securely and ensure that the horn panels are also tighly glued to the sides. I put the cab up on 2x4's so I can clamp to the opposing side, or in the case of putting that first side on, the opposing horn panel edge. Seems to work well as I had a ton of squeeze-out from the horn panel. I will buy some more clamps tomorrow at HF so I can at least work on two cabs/two sides at a time. One side per day is not going to cut it. On a related note: Summer has begun here in south Texas and it's 91F in my garage. The PL is loving it.

I am saving the one twisted-all-to-hell cab for last. Figure any lessons learned gluing up the first three will help me with that last one. Some pics.

I stapled in damping material in areas that will be hard to reach later. I have not put damping on the side panels yet, but may do that before continuing the build. No way I can get a staple gun up in the front of the cab and I HATE spray adhesive. It goes all over the place and never seems to grip securely when I use it.



Shot of the rear w/clamps.


Front with clamps. I debated long and hard about shooting brads through the sides into the horn panels for fear of splitting them. But I toenailed them in just right (so it seems anyway). Lots of squeeze-out on the horn panels. (wiped away already in this pic)


More tomorrow, hopefully.

[miked]

Bought six more clamps today. Twelve would've been better, but since I'm not in a rush I really couldn't justify the expense. So, the 2nd side of the first cab is glued on, and the 1st side of the second cab glued on. I'll probably start attaching the tweeter array mounting strips tomorrow.

Some sorta good news: Now that they're finally coming together, IMO, with judicious use of both top and bottom-bearing trim bits, my cabs should turn out pretty good looking. Between trimming off overhanging parts (still don't understand how the hell they are not totally square!), lots of Duratex and blacked-out grills, they should look really great from about 10 feet away.

I am using tons of PL to secure the sides and lots of clamp pressure and lots of brad nails. They will be air-tight and in the end, that matters more than how they look.

I did have to trim off about 1/4"-3/8" from the "point" of the triangular rear panel braces to ensure that they don't hit the frame (not the magnet) of the monstrous Delta Pros that I'm using. Based on my trial fitting and measuring, IMO Bill designed the braces to be 3" high so they would clear the frame of the largest driver by about 1/4" in a perfectly square cab AND assuming all your rear panel braces (the 1x1" sticks) are also pefectly inset by 1/2". My cabs are not perfectly square...or close...and I'd rather not leave it to chance that the braces will clear the magnet. Trimming off a 1/4" from the point (basically, JUST the point is now gone and the top is level like this ___ instead of like this /\ )won't hurt anything.

Thanks to a tip from Bill, I removed the rubber trim ring from around the magnet on the Delta Pros and that fixed the problem of the magnet not fitting in between the rear panel braces. I thought I was going to have to do major surgery, when all I had to do was peel off a rubber ring. Bill to the rescue. Thanks, Bill.

More tomorrow.

[miked]

Got two more sides on last night...looks just like the last pic I posted, so I won't bore you w/more of the same pics.

Tonight I plan starting the part I've been dreading; cutting the holes for the tophats. As you may recall, I plan on doing something different and putting the hat at the cab's COG, which in my estimation will be underneath the speaker basket, roughly centered between the front frame of the driver and the magnet. The plan is to bring the hat up through the cab and have it protrude into a hole in the frame, slighly into the cone area. It won't be anywhere near the cone...just sticking "up in there" through the frame. This negates the need to use a spacer on the bottom of the cab.

I thought briefly about having some metal stands made like the forum member in Australia (or South Africa?) has. Can't remember his name, but he runs a big rig; 4 tops per side. Those are nice stands. Mine would have to be foldable (or knock-down-able) and that would get pricey.

Now that I think about it, I may play around with designing a shelf with a tophat in it. Shelf mounts normally on pole/tripod, OTops sit on shelf. Hmm. The wheels are turning! Shelf would wind up being like 4 inches thick. If I made them out of 3/4" ply, they'd be heavy suckers. Possibly a shelf like that (20 pounds...guesstimation) and two Otops per tripod would be too much weight? Bah! Nothing is easy! I COULD make the box partially hollow....just have full-thickness ply surrouding the tophat itself to ensure a solid mount. Thoughts?

[Bruce Weldy]

Just let the tophat attach to the bottom of the platform. It just has to be the surface mount type. The it's just a single layer platform with a little ridge around it to keep it from slipping.

http://www.ultimatesupport.com/product/BMB-200K

[miked]

Just let the tophat attach to the bottom of the platform. It just has to be the surface mount type. The it's just a single layer platform with a little ridge around it to keep it from slipping.

http://www.ultimatesupport.com/product/BMB-200K

Thanks, Bruce. The problem is that thing is plastic and I don't trust it. I could see the actual pole mount part cracking after a few uses. If it was metal, I'd be all over it. I'd bolt that sucker on with Grade 8 hardware and be done with it.

But plastic mount with 80+ pounds (2 boxes) on top of it? I don't see that being a good idea. for a single cab it would probably be just fine with careful, gentle-ish use.

I'll probably mock up a shelf mount this weekend and eyeball how odd it looks...who knows? Maybe I can build in some lights or something into the front. I am thinking 3" or so thick, with a 1.5-2." high "shoulder" going around the two sides and back of the cab, just to keep it from sliding off. Also, the shelf will have indents where the feet go, so the cab would "sit in it." Just thinking out loud. Suggestions welcome!

[Tom Smit]

1 1/2" aluminum angle screwed to the bottom of a 1/2" plywood support plate? The plywood plate wood be the same dimensions as the top/bottom of your cab.

[miked]

1 1/2" aluminum angle screwed to the bottom of a 1/2" plywood support plate? The plywood plate wood be the same dimensions as the top/bottom of your cab.

Now there's an idea. It would be slightly less work than building a u-shaped "wall" around the base of the speaker. How well does aluminum take spray paint? IIRC, not too well. Now, steel angle iron takes paint well...but is heavy. But now I have more ideas than before, so thanks, Tom!

[Harley]

How well does aluminum take spray paint?

It has to be etched with an activator similar to this http://www.holdfast.co.nz/pages/product ... psid=19389 - that's for raw finished aluminium. If it's clear anodised ( still looks raw to the untrained eye ) then forget trying to paint it.

[miked]

How well does aluminum take spray paint?

It has to be etched with an activator similar to this http://www.holdfast.co.nz/pages/product ... psid=19389 - that's for raw finished aluminium. If it's clear anodised ( still looks raw to the untrained eye ) then forget trying to paint it.

Thanks, Harley. I'd be using the stuff they sell in the box stores here...so I guess it's anodized. Even if it's not, I'm not messing w/etching chemicals. With my luck it would react with the PL fumes, create a poisonous cloud and kill me. LOL! I tell you, this DIY hobby gets "more DIY" the further in you get!

[Bruce Weldy]

This is a good alternative that I've considered.

Scroll down a ways to see the drawing.

http://billfitzmaurice.info/forum/viewt ... +two+poles