4x T48 and 4x OT12 build

[dlv]

Thanks Seth! Yeah I don't throw any bits away. I toss 'em in a pile in the corner and I'm always digging into that for pieces to use for braces, jigs, etc.

[Keryn O'Shea]

..Templates make this so much fun..

..To take a bunch of garbage cutoff's and turn out a part that looks like it just came off the CNC table, such a sweet feeling. Especially once all the parts are made and look identical and perfect too. I love it!

Well done! Looks perfect!

Totally agree
Great attention to detail there mate, have you been witness to these cabs before you started building your own Dave?

[dlv]

Great attention to detail there mate, have you been witness to these cabs before you started building your own Dave?

Thanks Keryn! Nope never witnessed them (that I know of). I stumbled on Bill's site researching the idea of doing my own DIY built PA. On spec the efficiency of Bill's designs and testimony of you all on the forum here really impressed me so I went for it. So far I've only just done a quick little test with the first of the T48s I got together. It shook my whole shop so can't wait to hear the whole rig working together!

[Bruce Weldy]

Is there any need to square out the corners where the router bit leaves a 1/4" radius? I can't imagine it would affect the sound in any way. I like the look of the radius (though it'll be hidden eventually) so I'd rather leave it.

No need to square 'em up. Fine just like that. Great looking work!

[Keryn O'Shea]

..Nope never witnessed them.. can't wait to hear the whole rig working together!

You're in for a real treat then..

[commander_dan]

Mate, solid build thread! It's easy to see progress pictures and think how easily those cabs are coming together, but once you've built some you know just how much work has gone into each progress pic! Looking forward to seeing your herd fully assembled

[dlv]

Couple full days in the shop and got a lot done. Got the side on the last sub and all the access doors done. Just finishing and painting now is pretty much all that remains on the subs. Yay!

Cut all the parts for the 4 OT12's and started the assembly line.

Saw the guidance about using a jig for for cutting the 45 degree angle top hat clearance hole so I built one for my mill/drill. I don't have the right size hole saw so I tried using a Forstner bit on some scrap. It works out really well if you just go slow. Especially when breaking through the last bit on the bottom. My top hat is 1 5/8" OD so I'm cutting the hole with a 1 3/4" bit. The 1/8" clearance will probably be plenty for alignment with the hole in the cab bottom and easy to fill with PL. I should be able to index off the top edge of the piece and use the Y axis slide to line up the hole center with the same offset as the center of the hole in the bottom panel from the baffle. I'll let you know how that goes when I get to that step.

[Seth]

I haven't seen that method before. Looks like it came out perfect. Well done!

[dlv]

Happy to report the mill/drill jig idea worked out perfectly. Sharing a lot of detail on this in case it helps someone out there.

As planned I just indexed the point of the Forstner bit on the center line at the top edge (same edge that joins the baffle) and then backed the Y axis off exactly 1" using the dial. The same distance the hole center in the bottom panel is from the baffle front. The two holes lined up dead nuts. Table saw sled with the micro jig made the compound throat reflector panel angles easy as well! Worthwhile investment for sure.

Not everyone has an X-Y table on their drill press but I think you could do the same thing with a 1" spacer and a fence (piece of scrap or whatever) clamped to your drill press table. just set the fence with the jig indexing the bit point at the edge then put the 1" (or whatever your bottom panel center hole offset is) spacer in to move the jig back appropriately and clamp it down and drill. Just be careful to keep your center line (no X movement) on the jig. Using a 1/8" oversize bit leaves a little wiggle room in case you get off just a little but was easy to fill with a bead of PL.

Your drill press table has to be solid. Also you gotta clamp the jig solidly. There's quite a lot of lateral forces on the jig from the Forstner bit. They're not really designed to cut this way so go really slow. If the jig moves the bit will likely bind and bad things will probably happen. If you're using a hole saw that'll be less of an issue but you still don't want anything moving during the cut.

[Seth]

I'm still super impressed how well that came out. The edges and alignment came out so clean and precise, it's nearly like looking at the SketchUp model.

[dlv]

Thanks Seth. Maybe it's the "wannabe machinist OCD" in me. But I think it's paying off some. These OT12s so far are coming out nicely square. That makes me feel all warm and fuzzy inside.

[dlv]

Question regarding the damping foam inside the OT12s. Looking at the sketch up and build threads I do not see people putting foam on the backs of the horn panels. Only on surfaces facing the back of the driver cone (top/bottom/back/sides). I assume this is just to damp the direct reflections from the cone. Do I have this right? Just want to be sure.

Bigger question. How do folks usually go about fastening the HF horn in a CD build to the cab? I'm hoping to keep the outside of the cab clean there but I could use T-nuts inside the HF horn and counter sink some screw heads on the outside of the cab. Or is just a couple short screws in the top and bottom of the HF horn into the cabinet enough? I'm thinking a 1/2" flat head screw slightly counter sunk to keep it clean. Or maybe 3/4" truss head & grind the tips off so they don't poke through.

Another thought I had was do basically the exact same thing the melded array attaches to but set back appropriately for the HF horn positioning. Bill would this mess up the design? Attaching the horn to that would certainly give the most support. Seems like it wouldn't have any more effect on the midrange than the speaker grill mounts.

The idea of barely more than 1/4" of screw thread on four little screws holding the HF section concerns me a little. FWIW these 2" voice coil HF drivers I'm using have some heft to them. Been thinking about how they will ride in my trailer and the wickedly rough roads we have around here. Will be building a couple load in trunks each pair of tops will ride in. If they are on their sides (desired for both trunk size as well as access to the speaker handles) that puts the most lever strain on the horns from the load of the drivers from road abuse.

Probably over thinking this as usual. That's how I roll.

[Bruce Weldy]

Bigger question. How do folks usually go about fastening the HF horn in a CD build to the cab? I'm hoping to keep the outside of the cab clean there but I could use T-nuts inside the HF horn and counter sink some screw heads on the outside of the cab. Or is just a couple short screws in the top and bottom of the HF horn into the cabinet enough? I'm thinking a 1/2" flat head screw slightly counter sunk to keep it clean. Or maybe 3/4" truss head & grind the tips off so they don't poke through.

Probably over thinking this as usual. That's how I roll.

PL will hold it perfectly fine with no screws....tack it in with a brads.....assuming you are talking about the horn itself. If you are talking about attaching the driver to the horn, just use bolts into the threads in the driver itself. Can't imagine anywhere in the cab that you'd use T-nuts.

[dlv]

PL will hold it perfectly fine with no screws....tack it in with a brads.....assuming you are talking about the horn itself. If you are talking about attaching the driver to the horn, just use bolts into the threads in the driver itself. Can't imagine anywhere in the cab that you'd use T-nuts.

Yes was referring to the horn. I had it in my head the horn was supposed to be removable but given that's not the case and it's PL'd in there then I'm not worried. That stuff is stronger than the wood itself.

Thanks Bruce!

[Seth]

Just for reference, this is what the plans recommend;

The (compression driver) horn mounts centered in the cab, ½ inch back from the front edge.
Drill pilot holes for mounting screws or bolts through the cabinet top and bottom into the
diffuser brackets.
Install the horn after the cab has been finished.

It sounds to me like it is intended to be removable. Although, if the drivers are still able to be removed if it was permanently glued to the rest of the cab, I don't see a problem with that.