BillFitzmaurice.info

Officially beginning my Otop build. I plan to build 4 of the 1/4" Jarray cabs, two with melded arrays, two with straight, loaded with Beta12's.
Just finished cutting out the braces. I actually used 7-ply 3/8" baltic birch for them, since I have a ton of that rescued from EU pallet box shippers. They are pieces about 8x25 or 8x41. The shipper box covers were 5-ply 1/4" so I should be able to get most of the tops/bottoms/sides/baffles cut from them. Free plywood is such a help!
I made a cheesy little jig to cut out the braces. First cut the triangles, rough cut the rounded edge, and then trimmed with the router. Worked pretty smooth. Next I'll figure out some hole pattern to swiss cheese them and make them a little lighter. Need to go search for my hole saws...
Took a pic of the jig, but need to resize. Will post a little later.

You shouldn't need to resize the image, the forum will do it for you - unless it's absolutely massive....

Was hoping for more progress today. Oh well. Did cut down a couple 5x5 sheets for t30 sides, too.

himhimself wrote: ↑Mon Sep 03, 2018 11:45 am
I made a cheesy little jig to cut out the braces.

Better to make a cheesy jig that works, then to try and free hand everything. 10 minutes to make a jig, probably a couple of hours saved on the cuts and they are all the same.

Just the way it should be.

That's exactly how I make my jigs, brad nail/screw scrap pieces together, most times right to the table saw sled.

Gross rainy day, so am testing piezos. Made a little tester similar to one I saw a picture of here on the forum. Have checked all for polarity, only had one reverse and a few duds. Listening to sine sweeps now. 1500-15k over 4sec. Not exactly sure what i should notice to indicate a bad one. I've listened to a handful and they all sound about the same. Any tips? Thanks

Picked up a piece of 1/8 bendy Baltic yesterday from dsi indy. Great folks, highly recommend. Only $10 for a 5x5.

Built me a little family of xovers tonite. Slow...but progress.

Slogging slowly forward. Routered out my woofer spacers today from 1/2" baltic. Cut the sides, which were much more of a pain than I expected. Kinda wishing I would have taken the JackLite approach and made the box square like the Otop, just with 1/4" ply and bent horn sheaths. Oh well. Hopefully they will look okay when I assemble them. I still need to trim the 30" angle on the front of the sides. That's turning out to be annoying too - can't quite figure out a good way to do it on my little table saw. May drag out my circular saw and screw a jig to the side to rip it. We shall see. Hope to start trimming some piezos tomorrow as well.

Put the abrasive blade on the table saw and cut piezos down to size vertically. The jig worked pretty well. I tried gluing up the two straight arrays but it didn't go as expected. I used testors model cement, made for polystyrene and abs, and thought it would weld the plastic together quickly (like I remember when building airplanes and cars as a kid). Nope. Barely tacky. I put some PVC cement on the back side and they are kind of stuck together but certainly not melded into a stiff structure like I expected. I'll let them cure overnight as see how they look tomorrow. Got a bunch of cutoffs stewing in the PVC cement, so perhaps a thick, gooey application on the back side will improve the strength.

Model airplane glue isn't the same as when we were kids, probably to discourage sniffing it. The way to get the structure stiff is to apply a few coats of PVC cement to the back of the array over the course of a day or so.

Thanks Bill. It seemed stronger this morning, so I'll put some more thickened PVC cement on it tonight.

Glopping some thickened black cement on the back joints of the straight arrays has rendered them much stiffer. I glued up 8 3-packs of piezos for the melded arrays last night. I'll do the same with some more cement to get them more rigid, then make the 45 degree cuts. Only 3 fit in my jig, so that's why groups of 3.

Got my piezo arrays glued up. The melded didn't match up perfectly. One was better than the other, but was able to fill in the gaps with cut-off thickened cement pretty well. It will all be invisible when the diffuser rods get glued on. I also took a bunch of the little strips of ABS scrap and glued them on the backside to connect all of the tweeters together. That really added a lot of stiffness to the arrays. Ran a quick sine sweep across all the elements to make sure none were damaged during the cutting process and they all still worked, so I'll get them soldered up tonight and they'll be ready to go when I get around to assembling the boxes...maybe this weekend?

PIezo arrays all soldered up and checked. All still seem to be working, despite my crappy soldering. Forgot how much I hate soldering. Had a good friend back in the day who found soldering relaxing and could solder up amazing patch panels on a whim. Sure was nice having someone like that around who enjoyed soldering. I used to joke that he should pay me to let him solder my cabling projects...

Oh, I glued on the diffuser rods too. Trick I learned a while ago - coat the PVC with the purple primer before painting. Makes the paint stick really well. I made some path light extensions that way with 3/4" pvc. They been outside for years now and still look black like new.
Also, I had some stove bright (I think that's what it was called) high temp black temp paint laying around so I sprayed the rods with it. Has a slightly speckly finish that matches the textured finish of the tweeters almost perfectly. Not that it matters since I plan to add grills, but if someone is leaving them open, gotta say it looks pretty professional.