BillFitzmaurice.info

While I'm not a proponent of powered speakers for bigger PAs, they make sense in small settings. This SLA Pro will have the Dayton Audio PPA800DSP plate amp that will power the SLA along with a T24. The built-in DSP will make it a pretty easy setup to use. This little setup will be used for acoustic gigs, but could certainly do more in a small venue.

I'll also build in patching via speakons to run another SLA Pro from this amp and allow the SLA to operate in passive mode (for use with my old Peavey XR600 in my shop).

The amp will be installed into the back of the SLA without a separate box. It's an open-backed amp so it will have very little effect on the internal volume of the box.

This will require some alternate placement of the back braces to the main brace.

I'll try to impart some woodworking tips along the way beside just the regular speaker porn...

So, here we go....

Have to start with the obligatory pile of wood shot - all cut up and ready to go.
Fortunately, we have a local lumber yard that carries 1/2" BB now. Saves me a drive to San Antonio to my old supplier. $33 for a 5x5 sheet. I used to be able to rip one of the those sheets on my table saw by myself, but now I'm lucky to just get it out of the truck.

So, it went up on the saw horses and got taken down to a 28" piece. You can get 2 SLAs from a single sheet of 5x5. If you don't have a circular saw sled - build one. You'll use it all the time and makes for perfect cuts.

It's so important to lay out your cuts ahead of time so that you make all cuts of each dimension only once. By doing it this way - everything will be square. Once I had to panel down to a 28x30, I ripped all the 10" pieces, then the 9.5" ones, etc. Everything came out square....and I always do the corner to corner measurement to make sure it's right on.

Next up was the ports/handles. Drill the hole first, then be very careful with your jigsaw cuts and they'll come out pretty good.
I wanted the first hole to be as perfect as possible so I could use it as a template for the second one. So, it went on the oscillating sander for very, very light touchup to get it nice and straight.
Once that was done, I traced the outline on the other side, then rough-cut it with a jigsaw, then used my router with a pattern bit to finish off the other hole.
Since I might make another one of these sometime, it was worth the effort to grab a piece of scrap and use it to make a template for future use. The time to make the template was nothing compared to doing the first hole from scratch.

Here's the two finished sides are using a 1/4" roundover bit on the both sides to make the handle a little more comfortable.
Next up was cutting the holes for the amp and the speakon dish in the back panel. Nothing exciting - just rough cut it with a jigsaw - the edges will be covered up.
Years ago, I grabbed a piece of 3/4" scrap ply to use as a backer for routing speaker holes. I use double-sided carpet tape to hold my work piece to the scrap (a piece where the cutout is and a piece or two for the outside of the hole) - it keeps it all in place while doing the router cuts.

If you don't have a circle jig for your router - get one. I used a shop made one for years, but the store-bought jig is much easier to use and requires a whole lot less measuring. Here's my old circle cutting scrap board - there's been a lot of holes but on that thing...
The circle jig works great. I don't use a plunge router, I just take a small amount of material on each pass, so I can just raise up the router and turn it on, then slowly plunge it into the wood. I use three passes for 1/2". Takes a little longer but is safer than trying to take too much at once.
Haven't cut the holes for the tweeter array yet. The parts are all coming in two days, so I'll wait until I get it built before I cut the hole - just like the plans say.....

Next up was the main brace - just a simple 10x10" square with a could of cutouts. Used a miter fence on the table saw with the piece upright to make the 1" depth cuts, the used a rising cut on the saw to make most of the connecting cut. The rest was done with a jigsaw.
Because the main brace sits right up against the edge of the port/handle, I didn't want to hit a sharp edge reaching in there, so I did a little contour sanding on those edges to keep it smooth and safer.

Don't know why the pics look so clear on my PC, but get kinda' blurry once they hit the site - however, if you want to see 'em better, just click on 'em - they look better when blown up.

Next up - the brace modification and some more pics.....stay tuned.

Looking good Bruce.

Years ago I saw these corner braces in a magazine and promptly built some. I've had the two larger pair for many years and they have been a part of every speaker I've ever built - perfect for keeping panels at a 90 degree angle. The little pair I made last night just for this build. I wanted the back braces to be square to the main brace, so I had to build some small enough to work on the small braces.
Because the amp will be attached to the back panel, the braces in the plans have to be moved. I've going to use four braces located as close to the middle as they can be.

Here's the new little braces doing their work.....
Tonight or tomorrow I'll add the brace between the main brace and the baffle. The plans call for it to be done after the baffle is attached, but I've done all the pre-measuring and have made two spacers that will keep the ends of the baffle equal to the middle brace - so it will be square.

Next up is some padding on the panels.......really wish the parts would get here....

Nice project. Looking forward to your observations once you get it finished. Those 90 degree jigs are real handy.

I used the 90 degree braces to line everything up for a dry fit to make sure my measurements were all correct so that I could install the main brace to baffle brace at this point. I made sure my alignment spacers were correct so that when I install the baffle - the mid-point of the brace along with a spacers at each end will keep the baffle square.
Once it was all confirmed, I installed the baffle brace.
I'll get started on the dampening material next. Parts should be in tomorrow so I can make sure all the measurements are good, then I can start putting it all together.....except for the drivers.....gonna' have a finished cab for over a month before I can put in the speakers and see how it works.

All of the parts came in.....well, at least all the stuff I ordered in a hurry to get the amp for the good price....

Still have a few things to pickup.

Decided to start working on the tweeter array....

Many years ago, there was much discussion about testing piezos before using them. You should always buy more than you need, because some of 'em aren't going to be as strong as others.

I had saved the testing jig I built way back when I built my OT12 and WH10s.
Simple contraption with two solid copper wires attached to some speaker wire that terminates with both alligator clips and a 1/4" plug. I have a cable I built that ties the left and right of a mini plug together on a mono 1/4" that I can use to play my iPad through a single channel of my little powered PA head. So, I used the alligator clips to attach to the 1/4" plug. I keep Test Tones on my iPad - 60hz, 100hz, 1khz, 4khz. They are in my song catalog. Don't use 'em often, but it's really handy when you need 'em.

Anyway, I hooked it all up and ran a 4k tone through it. Took the piezos one by one and laid 'em on the two bare wires - that let me separate the wheat from the chaff. Of the ten that I bought to build this 6 tweeter array - one was really weak, two were OK, 7 were pretty even. I pulled the least "even" one to get my best 6.

Moral of the story - buy about 50% more piezos than you need and test them!

After testing, I got out the panel sled and put in on the table saw. Set a stop to cut 3/4" from the end. Ran one end then the other. Yes, the cutoff was on the side with the stop - but because of the low blade height and the short stop, it was plenty safe to do it this way.
You want to make sure the parts all lay flat and stay straight, so I put together a down and dirty jig for gluing. A piece of BB for the base and a scrap piece of 3/4 ply for the side stop. Then I put down the wax paper, laid in the pieces and used a small strip of BB to butt up to the other side. Once is was nice and snug, I tacked it down with 3 brad nails.
I found my old ABS glue from years ago and it looks to still be good, so I used a couple of the cutoffs as test pieces and glued 'em up. They are drying now - if they hold, I'll glue up the tweeters.

Bruce Weldy wrote: ↑Thu Nov 19, 2020 12:59 pm ...I found my old ABS glue from years ago and it looks to still be good...

I'm preparing for this process myself for the WH6 build. Haven't had the opportunity to do a glued array yet. What brand/kind of glue do you personally use? Would you mind posting a closeup pic of the front of glued seam after gluing, before any sanding/smoothing?

SethRocksYou wrote: ↑Thu Nov 19, 2020 2:54 pm

Bruce Weldy wrote: ↑Thu Nov 19, 2020 12:59 pm ...I found my old ABS glue from years ago and it looks to still be good...

I'm preparing for this process myself for the WH6 build. Haven't had the opportunity to do a glued array yet. What brand/kind of glue do you personally use? Would you mind posting a closeup pic of the front of glued seam after gluing, before any sanding/smoothing?

I'm using ABS glue....that's what used to be suggested. Now it's PVC Pipe glue according to the plans. May be the same stuff. But the ABS is black. PVC glue is clear....at least it was last time I used any.

Sure, I'll post pics. I'm heading out there in a minute to see if it's all dried and ready to go.

Bruce Weldy wrote: ↑Thu Nov 19, 2020 3:49 pm

SethRocksYou wrote: ↑Thu Nov 19, 2020 2:54 pm

Bruce Weldy wrote: ↑Thu Nov 19, 2020 12:59 pm ...I found my old ABS glue from years ago and it looks to still be good...

I'm preparing for this process myself for the WH6 build. Haven't had the opportunity to do a glued array yet. What brand/kind of glue do you personally use? Would you mind posting a closeup pic of the front of glued seam after gluing, before any sanding/smoothing?

I'm using ABS glue....that's what used to be suggested. Now it's PVC Pipe glue according to the plans. May be the same stuff. But the ABS is black. PVC glue is clear....at least it was last time I used any.

Sure, I'll post pics. I'm heading out there in a minute to see if it's all dried and ready to go.

I assume something like Oatey ABS plumbing cement. Thanks Bruce!

SethRocksYou wrote: ↑Thu Nov 19, 2020 4:02 pm
I assume something like Oatey ABS plumbing cement. Thanks Bruce!

That's exactly what it is....

Broke for a Mexican food lunch.....mmmmmm......

Got home and started gluing up the tweeters. Put a little on the edges, then smeared the back. They fit nice and snug in the little jig. Laid a 2x4 across the top to keep 'em locked into the jig and went away for awhile....

Seth, here's the glue joints front and back. I won't be cleaning 'em up as there will be a grill with a foam backing.....ain't gonna' be seeing nothin' back there.
Now it's time to cut the slot in the baffle for the array..... I borrowed my neighbor's calipers and did some measuring. I brought the straight line cut in to 1-3/4 instead of 1-7/8 (as per the plans). I wanted as much meat as possible for the screws to bite. The piezo housing is pretty wide due to the barrels where the diaphragms are attached.

Started with a 2-1/8" forstner bit after measuring the center point of the piezos. Drill out the 6 holes, then used a jigsaw to cut the connecting straight cuts.
After trying a test fit, I had to get the oscillating sander out and enlarge the length of the holes a little to make 'em more of an oval.
That let everything lay in there nicely.....

I guess tomorrow I'll start wiring up the tweeters and build the crossover. Then it's time to put in the damping and glue up the panels. Have a gig tomorrow night, so might not get a lot done.....got to rest up for a show at my age...

Thanks for the detail pics. Those came out nice. Much less out of the front that I thought there would be. Really clean Bruce. Good job