Building ewave SR w/PE trap cab, need ideas/advice

My next project is going to be some Econowave SR speakers using the latest Parts Express knock-down trapezoid cabinets.

Note that the woofer is bottom-mounted on the baffle. I plan to do the same (or similar), since the crossover design depends on the relative positions of the woofer and the compression driver.

The problem is that the current version of the knock-down cabinet has the baffle glued in place. I attached some pics of my cabinet below. If I just built them as designed, that would mean that my woofer would end up being stuck inside the cabinet.

In contrast, it looks like the cabinet that Zilch used had a baffle that was screwed into place, and was thus removable. You can still see the old version of the cabinet on PE's site, here:
http://www.parts-express.com/pe/show...25&FTR=245-325

So I am wondering how I can mod the cabinet to allow me to service the woofer. It seems like I have 2 basic options, with several possible variations of each:
1. make the baffle removable somehow
2. top mount the woofer, but keep the relative driver positions as designed by some combination of building a woofer recess and/or extending the front of the baffle under the waveguide

What would you do, and how would you do it?

Thanks,
-Max

Good idea. I will test it out and see if that will work. With that big waveguide, I think it will.

-Max

The driver will easily fit through the hole for the waveguide. Thanks for the suggestion lilmike -- you really saved me a lot of work, and I think the end result will be much better without having to make a removable baffle.

But I think it will be really, really tight trying to get the fasteners installed. I haven't actually tried it yet, but just looking at it, it seems like it would be very frustrating or maybe even impossible. I don't think there will be a lot of room in there, and getting the screws on the sides and the bottom seems like it would be rough.

So, my plan is to make a wood ring with an ID of 11" and an OD of ~12.5 and put 8 hurricane nuts in it. To install the driver, I will screw through the front of the baffle, through the driver frame, and into the nuts in the wood ring, behind the driver.

Does anyone see a problem with that approach?

-Max

I decided to get started tonight, so this is now my build thread. I am starting by building just one speaker. I'm not under any major time constraints and I figured that I might forget something and want to place another order at Parts Express. The second cabinet will get me most of the way to the threshold for free shipping on my second order.

I was originally going to build the SR Compact variant, but then I found some QSC 152i waveguides from a private seller and decided to build the normal SR variant instead. I'm planning to use these outside at Burning Man. It takes a lot of power to make loud music outside, and I'm using a home audio receiver, so the greater sensitivity of the SR model seems like a useful benefit. I'm not really planning to play them that loud, but at least the option will be there if we want it. In years past, I had some speakers in a board, open baffle style. That setup was just haphazard rather than an intentionally designed audio system. But we basically ran the receiver at high volume (on the threshold of major distortion) and it wasn't very loud. I doubt we'll have that problem this year.

tl;dr -- long story short: I already have all the drivers and the crossover parts for both speakers. The crossover for the SR and SR Compact are different, so I'll probably go back and build the SR Compact as home speakers as a later project. (I'd like to do some towers with a squarish shape and finish similar to Zu Omens.)

I was hoping I could use the threaded compression drivers that I bought originally and use an adapter to attach them to the QSC waveguides, but I think this isn't such a good idea since it moves the driver. It seemed like the acoustic center is an important part of the design. So I'll probably end up ordering a pair of bolt-on compression drivers for my first build and use the threaded ones later when I get around to building the SR Compacts.

Tonight I made the wood ring that will hold my hurricane nuts so I can screw the woofer in place from the front of the baffle, even though the woofer is mounted behind the baffle. I plan to countersink the holes on the front baffle and use flat head 10-32 screws.

I used 1/2" Arauco plywood -- I reused the circle I had cut out for the MFW-15 woofer in my THT LP build. I wanted the ring to be 11" ID and 12.5" OD, so I screwed the wood to a backer board in two places on a 11.75" bolt circle. The holes I drilled would become the pilot holes for two of the woofer fasteners, too. Then I used the Jasper 200J circle jig on my router to make both cuts. For the outer cut, I used the hole marked 13" since my bit is 1/4" -- the result was 13" - 1/4" - 1/4" = 12.5" like I wanted. For the inner cut, I used the 11" cut to get 11", as normal.

Once I had the ring cut out, I spring-clamped it to the woofer to mark the rest of the holes. I used the two holes I drilled to hold the plywood to the backer board while routing as two of the driver holes, too.

Then I center-punched the holes, drilled them with a small (3/16") drill and finally with a 1/4" drill, which is the size needed for the hurricane nuts.

Once the holes were drilled, I used the ring to mark the holes on the speaker baffle. Unlike most of my other speaker mounting jobs , I was careful this time to line up the holes so that the bolt pattern would be square to the baffle and not at some random driver rotation angle. Once I had it lined up, I held the ring in place with some spring clamps and used a center punch to transfer the positions to the baffle.

Then I mixed up a little epoxy and put a little dab on each hurricane nut before tapping it into the ring with a hammer. I was being careful not to get any epoxy inside the threads, but I didn't actually check how well I did. I guess I can always drill and tap the insert if I happened to mess one up.

I have the hole for the waveguide laid out on the baffle, but I didn't get around to cutting it tonight. My plan is to cut a jig out of some plywood, clean up any mistakes in the jig, and then use the jig and a top-bearing trim bit in my router to cut the hole in the speaker baffle. I know I am making this more complicated than it needs to be, but I'm having fun learning about my new tools and trying different techniques.

-Max

The ring does not fit snug enough that it would stay in place on it's own.

My plan is to lay the cabinet face down and hang it over the edge of a table. I will slip the woofer through the waveguide hole and then move the driver and wood ring into position to start the top two screws. Once I get those in and the driver is held in position, I can flip the cabinet up and install the rest of the fasteners.

-Max

The main issue with this build is that the driver mounts to the back of the baffle. And once I glue the cabinet together, the baffle is not removable. It is pretty cramped inside the cabinet, so I made the wood ring so I don't have to fiddle with 8 separate fasteners inside the cabinet. With the ring, I can install the screws from the front of the cabinet. Using the t-nuts will give the screws something to grab, and will make it less likely that I'll split the wood ring.

Who knows, I might end up having to remove and reinstall the driver. And I'm generally not opposed to a little over engineering in my DIY projects.

-Max

Here's how the driver will be mounted -- sandwiched between the baffle and the wood ring I made with the hurricane nuts in it. I didn't have the screws yet, so it is just sitting there in the first shot.

Then I went and got screws. I chose flat head screws since the waveguide comes right up to the edge of the woofer hole, and I figured that flush-mounted screws would avoid those reflections that speaker designers talk about. I got flat head 10-32 x 2" long screws.

My previous uses of my countersink bit have shown me that I'm not very consistent with the depth of the countersink. But this time I wanted to get consistent countersink depth. So I found this countersink bit set at Harbor Freight that has an adjustable stop for the countersink depth. The stop will hit the front of the baffle, so this probably isn't a great solution for high-class finishes, but it doesn't really matter for my case. I first did a test drill in a piece of scrap wood. These bits are pretty cool -- they are tapered to a point, and the bit doesn't walk at all. I dropped one of my screws in my test hole, and the surface was nearly flush -- close enough that it should be perfectly flush once I snug the fastener. The stop didn't do much damage to the surface, either -- it just smoothed it out a little bit but did not tear it up at all.

I had already drilled 3/16" holes in the baffle, which is almost big enough for the 10-32 screw to drop through, but not quite. The #10 countersink drill bit in the Harbor Freight set is a bit larger in diameter and the screw will drop right through the hole. I also have other #10 countersink bits and the drill is much smaller -- small enough that the threads on a wood screw will dig in and hold, which seems to be exactly what it should do. The Harbor Freight bit set says something like "tapered drills for wood screws", but it seems really weird that a #10 machine screw will drop right through the hole drilled by the #10 countersink bit. Keep that in mind if you get the HF bit set -- the bit size seems to be much larger than the label would suggest. But it is the perfect size for my use here -- I want the screw to drop right through the holes. So I used the #10 bit and countersunk all the woofer screw holes in my baffle. All the holes turned out great, with consistent countersink depths. The bit does get full of sawdust though -- need to clean it out with something pointy after a few holes.

I bolted on my wood ring without the driver for a test fit. It went right on with no problems. I also ran the router around with a flush trim bit. It cleaned up the driver hole in the woofer baffle a little. The edges of the CNC cuts from the cabinet kit are a bit rough. It was still a little rough after I hit it with the router, so I ended up sanding it a little bit as well.

I debated whether I should round-over the edge, but I decided not to. The smallest roundover bit that I have is 1/4". It would probably hit the screws, though I could just remove them before running the roundover. The bigger issue is that the waveguide edge comes right up to the edge of the woofer hole. So I decided not to roundover the edge, but just softened it with a little sandpaper.

-Max

(I know I'm writing a lot of detail into my build threads, but I figure that someone might point out a better way to do some of it, and that it could be useful to someone else who is just getting started -- kinda like me a few weeks ago. )

I've been thinking about how I want to cut the hole for the waveguide. I'm not trying to find the easiest way to do it, but rather some way that lets me try a new technique with my tools.

I realized that my original idea of using a top-bearing flush trim bit with a template is not a very good one, since the baffle is 3/4" thick. I'd have to either make a very thick template or cut all 3/4" in one cut so that the bearing could ride on the template. So I scrapped that idea.

My next idea was to use a guide on the router with a template. I bought the Bosch guides that work with my router. And I have a 1/4" up spiral bit. So I figured that I would use the 1/2" OD guide, which means that I would add 1/4" to the dimensions of the waveguide cutout when making my template.

So I grabbed a spare piece of 1/2" Arauco plywood and started making my template. It seems like people always say to use a circular saw for stuff like this -- driver access panels, etc. So after I drew out the lines for my template, I grabbed my circular saw. My circular saw is setup with the base for the EZ track so I grabbed the track and lined it up on my template. In this case, I didn't really use the track edge directly since I wanted to clamp on the other side of the cut. But the edge was still useful as a reference -- I just clamped the track 1/8" or so away from the line and kept the edge parallel with the line.

To get the saw ready, I retracted the blade since I would be plunging into the surface rather than cutting from an edge. I also removed the zero-clearance insert from the EZ saw base, since it was blocking my view of the cut on the front edge. I setup a bright work light, too, so I could really see where I was cutting.

Once everything was lined up, I loosened the plunge lock on the saw, started the saw out of the wood, and then slowly plunged the blade into the wood. I then moved the saw forward and back almost to the lines that marked the ends of the cut. I lifted the blade out of the wood and then let go of the trigger. I did the whole cut with the plunge lock loose. I don't know if that is the right way to do it, but it seemed to work fine. Then I did the same for the other three sides.

To complete the template, I used my jig saw to cut out the wood that remained at the corners -- the stuff you can't cut with the circular saw. It came out pretty good. However, I did chip the wood in two of the corners by stupidly lifting the jigsaw away before the blade had completely stopped. You would think that I would have learned after chipping the first corner, but I guess it takes me two times before it sinks in.

-Max

Once I was done making the template, I screwed it onto the back of the speaker baffle. I put it on the back of the baffle so that the screw holes would not be visible on the front of the baffle. I had already marked the lines for the waveguide hole, so I just lined up the slightly-larger template by sight to position it. I added some spring clamps to hold it in place, but I can't run the router around it with the spring clamps in place. So I drilled a couple of holes with the countersink bit (not too deep!) and screwed the template into the place with screws that were short enough not to poke through the front of the baffle.

Time to setup the router. Hmm... I had not anticipated some of the problems here:

Problem #1: I have the router guides, but I don't have any way to attach them to my router! It turns out that you also need part RA1126 to use the guides on the router, which Amazon doesn't even sell. Lame!

(Possible solution: I bet this guide set from Home Depot would work: http://www.homedepot.com/webapp/wcs/...ocStoreNum=640)

Problem #2: I also realized that my 1/4" spiral cut bit has a 1/2" shank. I slid the 1/2" OD router guide onto the bit and found that less than 3/4" of the bit was exposed before the guide contacts the wider shank on the bit. So I really should have cut my template to work with a larger diameter guide. Either that or I could use a bit where both the cutter and the shank are 1/4".

So I don't think I am going to use my template to cut the waveguide hole after all. I might get the Bosch part and 1/4" bit and try it for the second speaker just to get some experience with router guides.

On the plus side, I gained some useful experience cutting the template. I'm going to cut the waveguide hole with the circular saw and jig saw. It was pretty easy to do, and I am confident that I can do it without messing up my speaker baffle. That will be my next installment.

-Max

I cut the waveguide hole in the baffle tonight, using plunge cuts with my circular saw, a jigsaw to finish the corners, and a little sanding to take the edges off. It turned out fine.

That sounds better than using a circular saw, but I don't have a table saw.


I've been thinking about how I will finish these cabs. I was planning to glue on some carpet, perhaps in a weird color. But then I got to thinking about how much dust the carpet will collect at Burning Man and decided to try some kind of paint instead. I read a lot of raves about Duratex. But I want these to be something other than black, since black is expected, and the unexpected is good at Burning Man. They would also get very hot in the sun if they are black. So I ordered some white Duratex from here:
http://www.acrytech.com/catalog.asp?prodid=554522

Maybe I'll paint some bacon on them, too, to coordinate with my bacon sub.

I ordered some of these white handles, which seem like a bargain:
http://www.parts-express.com/pe/show...number=269-263

The first L-PADs I bought are long enough to install through the 3/4" plywood, but they also stick out and I'm worried that they will break during transport/handling. I could put them on the front, but I'm going to make a grill that screws on, and I don't want to have to unscrew a grill to adjust the L-PAD. I suppose I could also eliminate the L-PAD with the appropriate components, but I figure it will be useful to experiment with. So I ended up ordering these shorter L-PADs with recessed mounting plates:
http://www.parts-express.com/pe/show...number=260-252
http://www.parts-express.com/pe/show...Number=260-268

And finally, I'm going to use these terminal cups:
http://www.parts-express.com/pe/show...number=260-285


Questions:

Should I "paint" the inside to protect the wood? Perhaps just with watered down Titebond II or something?

Should I install ports? I will be using these with a sub. The build summary doesn't show any ports. No ports means less corrosive playa dust inside the cabinets, too. I'm planning to run them sealed unless someone makes a case for installing ports.

-Max

It feels like a waste of Duratex to use it on the insides, though. I've got a bunch of Kilz primer. Maybe I will use that on the insides.

I found this SR build thread by Cerdic that used 4" long x 4" diameter ports. I do happen to have some 4" plastic pipe. And I want impact. So maybe I will put a port in the back or something.

That thread reminds me that I'll need some batting for the insides, and that I should consider damping the waveguide. I've got some B-Quiet Ultimate, so I'll use that on the waveguide.

-Max

Excellent idea! I will paint yolks on them. And some pepper spots.

-Max

Fair enough. I still think they make sense for this usage, as unique as it may be. And I'm not afraid to drill or cut the head off an ornery fastener if things go bad.

-Max

I got busy with some other things, but will be working on these again in a week or less.

Christopher, thanks very much for the info. I want these to be able to blend with a sub using an ~80Hz crossover, so I'll definitely need a port.

-Max