SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

Hey folks, mid-day update over the lunch break. I have the test wiring panel finished and installed on to one of the cabinets. I had to change the wiring scheme a little bit because I only drilled a hole large enough to pass one pair of 16AWG signal wires through the coax chamber. I tried stuffing four twisted / doubled-up 18AWG wires with through that hole and found out that wouldn't work pretty quickly. The easy solution was going to four straight 18AWG wires instead of 8 (+/- for mids and +/- for the HF), so that will have to do for now. The woofer section was wide open, so no issues at all with my twisted pair of 18AWG wires to give approximately 15AWG to the woofers.

I used some gasket tape for the coax section for the Celestion and the built-in gasket on the Estoterics to seal up each respective driver. The coax chamber got about 8 oz of polyfill for the ~0.4 cuft of space it had, while the ported woofer chamber got a lining of 1" thick project foam from wally world. Overall driver install went well. I only had to use my tap kit to clean out one of the 10-24 threaded inserts on the coax chamber. For the cosmetic benefit of using machine screws and multiple on/off installations, those little buggers can get mighty particular about thread-ins! Gotta be careful not to snag one and accidentally twist it out of the MDF hole it lives in.

The last thing I learned at the end of the night is that my Dayton Audio speaker stands may be a bit undersized for these stand-mounters. I didn't feel very comfortable putting this cabinet up there. Took a few attempts at positioning the speaker on the stand to get the balance point right, and the footprint of the stand felt smaller than it should be. I will definitely need to add re-worked stands to my to-do list so these cabinets have a stable permanent home in the future!

[KEtheredge87]

One thing I would suggest, before painting the sidewalls, apply some Zinsser Seal Coat to the veneer or finish the veneer in whatever finish choice you have planned. By doing that, if any of the black paint was to get on the veneer, you could clean it off without a lot of effort. Without a finish on the veneer, not much chance.

Thanks Kevin, That's a great idea! I know there's going to be some kind of dye finish applied, and putting down some seal coat will definitely be helpful before painting. I was already planning on using a lot of delicate surface masking tape with edge lock feature to protect the veneer, but this takes it one step further.

[Kevin K.]

Since your joints are rounded over, I think you'll be fine and not have much issue with "ghosting". Flat butt joints would be a different story. As for the mismatch, why didn't you apply some masking tape layers to the core before routing to allow for the .020 difference?

Edit: Never mind the mismatch question, I forgot you were planning to extend the veneer past the core and trim it back afterwards. One thing I would suggest, before painting the sidewalls, apply some Zinsser Seal Coat to the veneer or finish the veneer in whatever finish choice you have planned. By doing that, if any of the black paint was to get on the veneer, you could clean it off without a lot of effort. Without a finish on the veneer, not much chance.

[KEtheredge87]

For MDF stabilization you want to try to get the excess moisture out. Plus you want the PVA glue lines to shrink. Some people have baked them similar to kiln drying. I've put a fan on them for 2 weeks inside the house. I've not noticed any difference in ghosting

Thanks John!

Seems like I am destined to have some amount of ghosting just based on the design choices I've made. I hesitate to do two layers of veneer on the center parts of the cabinet as a means to control ghosting. The main veneer layer will already be 20 thousandths or so above the sides of the cabinet (since those will be painted and not veneered). I'd prefer to keep the difference in dimensions as small as possible so it's not as noticeable to the hand / feel or to the eye with several layers.

[jhollander]

For MDF stabilization you want to try to get the excess moisture out. Plus you want the PVA glue lines to shrink. Some people have baked them similar to kiln drying. I've put a fan on them for 2 weeks inside the house. I've not noticed any difference in ghosting

[KEtheredge87]

As promised - a second post about the testing panel for individual driver connections. I had to get a bit creative here since I wanted the ability to connect to individual drivers without having to constantly swap the hookup lines on the coax driver. Since I already cut the hole for my dual binding post terminal plate, I couldn't just drill a few small holes inside the area that would eventually be gone. I needed something that would use the screw holes I already had AND would seal up against the cabinet. Time to get creative.

My first thought was a 3 speaker wall plate that's used as a pass-through in home theater to hide wires within the walls. Those are generally cheap, ~$8 on The Zon, so I ordered one. As expected, the binding posts are totally hollow, which is a giant leak path and thus a problem for my use. Thankfully it is an easily addressed problem. I simply took all the binding posts out of the plastic plate, notched a hole in the side of an RTV silicone sealant tube, and shot silicone into the hollow from one end while a dowel rod blocked the other side. Air-tight seal number 1 - check! From there, I put a bead of silicone on the plastic mounting plate under each binding post and re-installed those snugly. Air-tight seal number 2 - check!

At this point, I cut two 3ft sections of 10 conductor 18AWG wire that I had laying around. I stripped the main jacket off and separated all the conductors. I took the two wires of matching colors and used my drill to make some nice twisted wire sections to equal one 15AWG wire for use with this test panel. I went with the color coding scheme I've seen in some kits, positive leads being blue/purple for woofers, yellow for mids, and red for high frequency. The negative leads are black, grey, and white.

Once those wires were connected to the inside facing binding posts, I ran another bead of silicone along the perimeter of the plastic plate and screwed the plate to the MDF carrier to make air-tight seal #3

The final seal (yes... 4 different sealing operations here folks...) will be some speaker gasket tape on the MDF outside the perimeter of the screw pass throughs. I am securing this test panel to the back of the cabinet using the same screw holes and threaded inserts that the plastic terminal cup will use. I clamped the carrier to the cabinet and used a tiny transfer punch to mark the hole locations on the MDF carrier. That let me line things up perfectly.

So... Was this convoluted? Absolutely. Effective? I hope so. Fun? You betcha And that's what matters the most!

[KEtheredge87]

Good Evening, Everyone!

I'm happy to report it's been a successful weekend in the garage I was able to get all the woodworking done on the speaker cabinets, clean up the mountain of MDF dust from all the router work, create a sealed-up test lead panel to individually connect the LF, MR, and HF driver sections for testing, AND repair a little easel from the "honey-do" list!

I'll put another post out for the test lead panel after this one. For now, let's talk MDF dust! I had to pull out all the current big guns in my router bit arsenal for these tasks. I used the 1/2" spiral flush trim bit to trim the side panels flush with the core of the cabinets. I was a bit over generous and gave myself 1/4" overhang on all side panels. In retrospect, I should have planned for 1/8" overhang. While it would have been a bit more work to line it all up during the glue and clamp stage, it would have saved a LOAD of time and effort in the flush trim stage.

After I got the flush work done, the jigsaw was used to rough cut the slot port opening just wide enough to get the 1/2" spiral bit down inside the slot. This was done to gain access to the slot port I had glued into place behind the front baffle previously. An initial rout was completed to get the slot port open, then I used chisels to clean up any glue that was dried on the surface down inside the slots. These glue bumps were translating to my slot cut since they were in the bearing's path of travel. A second rout after clean-up solved that issue and straightened up the slots nicely. A final router pass with a 1/4" spiral flush bit was used to reduce the radius in the corners of the slot ports from 1/4" down to 1/8".

The next big bit was my 3/4" roundover bit to shape both the top and bottom short edges on the front and back of the cabinets. Several test passes on a 2x4 chunk were used to dial in the height. I used the fixed base for my router because I don't feel like I have as much control over the bit depth with my plunge base. I set my router depth once with the fixed base and do all the cuts I need at that time. I'm guaranteed a consistent depth of cut across the project this way. The cuts themselves went well. Thankfully MDF machines easily, so I didn't have to take multiple passes on each edge to nibble out the profile. I kept a slow feed rate and constant eye on the job to make sure things went well.

Finally, the last big bit was a chamfer bit capable of a true 1/2" chamfer @ 45 degrees. Granted, I only needed a 3/8" @ 45 degree chamfer, so that cut wasn't nearly as demanding as the 3/4" round. I think this chamfer adds a nice bit of visual interest!

From here on I will be focusing on initial measurements. I'll be honest... I've gotten attached to my test cabinet, and planning for him to be a fully fledged contributor to my audio stable. That would make this a 3 speaker set, which I would be happy to use with an acoustically transparent projector screen in my basement as a proper center channel / LCR style setup. With respect to measurements, that means I will get one set of measurements now WITHOUT the final perimeter slot cut / veneer trim running through the front baffle. This may or may not have a meaningful impact on baffle diffraction, but we'll have measurements before and after to see!

Now if I could only figure out how to accelerate any kind of MDF baffle seam creep before I got into veneering! Wonder if leaving the cabinets in the bathroom while a steaming hot shower runs would help? Maybe running a warm air humidifier in their general area might do something? I figure moisture content is key since that's part of how wood expands and contracts, but I don't know if the material returns to it's previous state after a swell, or if it retains some dimensional changes.

Enough talk... more pictures! Enjoy!

[Kevin K.]

Don't have enough experience with the different damping materials to say which one is better. The denim insulation is what we ended up using in the Black Widows and it seemed to be the most effective based on measurements. Lots of different opinions out there and many users of the polyfill so I suspect you'll be fine.

I understand your approach now, thanks for taking the time to explain. Wonder how the slot will impact diffraction, guess we'll see when you get to the measurements. Good luck!

[KEtheredge87]

Keith, what damping material are you planning for the coax compartment? And I'm still trying to figure out your finish approach. Would have thought you'd veneer wrap the core of the cabinet before attaching the sidewalls since they are going to be painted. What's your plan?

Hey Kevin, The coax department is going to get a healthy stuffing with polyfill to match up with BassBox's expectations. I've never experimented with anything else like fiberglass or that neato looking blue jean based insulation. Do you know if one of those is better than the others?

Beyond that... let me try to explain things a bit more on the veneer. I thought about adding my side panels after veneering like you suggested, but I expected to run into some issues. For one, I wasn't sure how to produce these panels with an undercut to make the slot, and then properly align them while gluing up. This seemed a lot more complicated to me than building out the boxes, getting all the side panels flush trimmed, then dressing up the edges. I also wasn't sure about applying veneer over the cabinets then trying to use a down-cutting spiral bit to trim veneer and make a slot at the same time. This would work OK on flat parts, but going around the rounded edges seemed impossible.

All of that mental mess led me to this order of operations:
1) Glue up the cabinets and flush cut the side panels (My plans for this weekend)
2) apply 3/4" roundover to the short edges on the front and back of the cabinets (maybe also this weekend)
3) apply 45 deg chamfer to all edges of the side panels
4) take a pencil and mark a "landing zone" that's ~1/4" wide around the cabinets (This is where the veneer edge must end and the slot cutter must travel)
5) Apply veneer
6) use 1/4" slot cutter with large bearing to limit slot depth to 1/8", Cut a slot with a climb cut technique to push veneer fibers INTO the cabinet during the cut rather than pulling them AWAY from the cabinet causing tearout.

Here's a quick and dirty diagram showing what I am trying to achieve. Hope this helps! If I'm still not clear, just let me know and I'll try again to explain my thoughts.

Thanks for following along!

[Kevin K.]

Keith, what damping material are you planning for the coax compartment? And I'm still trying to figure out your finish approach. Would have thought you'd veneer wrap the core of the cabinet before attaching the sidewalls since they are going to be painted. What's your plan?

[KEtheredge87]

Another day, another update.

This should be the last "run-of-the-mill" glue and clamps style update for a while. From here on out each cabinet operation will be an obvious and noteworthy step toward the final design, and we will finally get into the technical nitty gritty of measurements and XO design!


Tonight's work was simple but important. I took silicone caulk to the inside seams of the cabinet as extra insurance that all gaps between the two driver chambers as well as gaps between those chambers and the outside world were completely sealed up. The amount of wood glue I used should have done that job well enough, but I'm not going to pretend my joinery cuts and panel machining are THAT good!

Once I had all the caulk in place, I flipped each cabinet over so I could pour epoxy into the dowel holes on the other side wall. Thats it! From here forward I'll need to cobble up some test wiring (hopefully with that 6 banana post wall outlet that I mentioned yesterday) so that I can exercise each part of the three-way system independently without constantly swapping driver wires around on the coax.

More pictures for you all. Thanks for following along!

[KEtheredge87]

Holy Clamps, Batman!

I think I hit a new shop record for most clamps in use at one time. Tonight I glued the other wall on to each of my three cabinets, using twelve clamps + two "gravity clamps" each. That brings me to a record 36 bar clamps, or 42 total clamps! Tomorrow I can flip the cabinets over and add some more epoxy to the other side of the dowels to really fix them into place, as well as run some silicone along the seams inside the cabinets. That should set me up for a lot of flush trim work on Saturday, and maybe even adding the 3/4" roundover to the narrow edges of the cabinets!

Outside of actual cabinet construction... I'm thinking about a way to make a six binding post temporary test terminal so I can wire individual lead pairs to the woofer, coax mid, and coax HF drivers. Since I've already cut my recessed space for the terminal plate that only has two pairs of binding posts, I'll need something that I can secure over top of that space. I ordered a home theater wall plate with 6 binding posts off The 'Zon, so when that arrives Friday I'll try installing that in some 1/2" MDF, or thinner hardboard. I'll post some pictures of whatever I cobble together. For now, here's some photos of the whole clamp army battling against the cabinets!

[KEtheredge87]

Hello again Everyone! I refuse to let this cold bug get the better of me. Tonight I made some "square dowels" at the suggestion of jhollander so I didn't have to make another trip to the hardware store. Thanks again for the suggestion!

I also attempted to use my marking dowel tools with the blind nails in them, but quickly figured out that wasn't going to be anywhere near accurate. I had planned from the beginning to epoxy these dowels into place, so I purposely used a 1 1/8" OD forstner bit to make the dowel recesses. Asking three 1" dowels to stand still inside 1 1/8" holes while I positioned a board on top wasn't going to happen, so I aborted that mission and went back to old fashioned measuring and marking on my boards. This worked out much more accurately, and gave me the right line-up between the recesses.

Once the recesses were drilled and the dowels test-fit was complete, I mixed up several small batches of 5 minute epoxy and jammed as much as I could down into each dowel recess (bottom side only). I'll let this dry overnight, then I can work on gluing up the other wall and epoxying the other side of the dowel into place.

At this point, I find myself pretty impressed at how heavy these stand mount cabinets are becoming. I didn't really have a good idea of what to expect in mind when I started. I think I should have no issues with cabinet resonance!

[KEtheredge87]

You can always use square dowels

Oh right! I've got lots of square dowel stock in my scrap bin. Thanks for pointing out the obvious solution. 😂 -- Sent from my SM-N900V using Tapatalk

[jhollander]

You can always use square dowels