SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

I love it! I'm going to have to build a sled like that!

Question: why is the back of the mid enclosure double wall?

Hey Craig, The only reason the mid enclosure is double wall is because I was targeting specific volumes from bassbox for the coax and woofer chambers, and I didn't want to change my external dimensions to account for it. That extra layer of MDF just fills up some internal volume. I probably could have gone single wall and saved myself a load of trouble, since the math works out to a ~3.8% increase in woofer chamber volume with only one layer of 3/4" MDF.

Alternatively...I'm just a glutton for punishment.

On the sled bits... yeah, it turned out much better than I would have guessed for a 10 minute DIY effort. I used this Wood Working Web video from Colin Knecht as my guide.

https://youtu.be/r4FNdr1VO0M

[jhollander]

Ah, well, land the panel at the top of the cabinet -30 degree, gives time for a beer. Square off the mid box and vary the insulation, 2 beers, but not nearly as interesting.

[skatz]

Too late to help you now since you've already made the cuts, but I was thinking, could you have fabricated the part by cutting the two thicknesses of MDF separately and then laminating them together afterwards? Its the double thickness that forces the cut to be so long. Or if the second thickness is just to take up volume, it could just be an appropriate sized block sitting inside of the cabinet, you would just need to make it the right volume to occupy in the enclosure.

[KEtheredge87]

Too late to help you now since you've already made the cuts, but I was thinking, could you have fabricated the part by cutting the two thicknesses of MDF separately and then laminating them together afterwards? Its the double thickness that forces the cut to be so long. Or if the second thickness is just to take up volume, it could just be an appropriate sized block sitting inside of the cabinet, you would just need to make it the right volume to occupy in the enclosure.

Hey Skatz,

Those are great thoughts! I had considered some kind of bevel cut - then laminate kind of arrangement. It would probably work out well with the right clamping arrangement. My engineering neuroses drove me to glue then cut so that I was sure the surfaces didn't have some kind of step in there where I glued after cutting. The block for volume is a great simple idea too. Doing things as I have made this fat wall a decent brace too. I'll look for the silver linings in my own craziness

[Wolf]

My vertical jig is very similar to what you made, and rides the fence on the table saw. The problem I had most in use was alignment of the setup. Shift it a smidge and it was no longer perpendicular. I had to hold it and clamp to it just so to get exactly as I wanted.

Glad you got through it with the result you wanted, and that you did it safely.

Later,
Wolf

[KEtheredge87]

Hello Everyone, Update time!

Lots of detail work progress this weekend. First, I trimmed up the slot port tunnel that I made on Friday and gave it some 1/4" rounds to help flare the inside opening as well as make the whole thing a bit friendlier to the touch when I'm digging around in there later. The delicate part was making the slot cut through the front baffle to match up with the slot tunnel on the inside. I had to make some layout lines inside the cabinet to get the port centered on the inside face of the front baffle. From there, I drilled some holes through the front and jigsawed away as much material as I could to let a flush trim bit reach down into the tunnel. I tried a 1/4" flush trim bit to start, but it didn't have enough cutting length to reach all the way through. Lucky for me I have a gigantor 1/2" flush trim bit from my Jedi Mind Trick subwoofer project that WAS long enough. I switched back to the 1/4" bit afterwards to clean up the corners. This was important because there's still a slight lip on the inside corners of the port tunnel where the front baffle transition happens. leaving it with the 1/2" bit left a larger lip. Using the 1/4" bit to get the 1/8" radius in the corners should help blend that in considerably.

Here's a few pictures from the woodworking adventures this weekend. Next post will have veneer info and initial port tuning!

[KEtheredge87]

Post number two for today: Veneer and Port Tuning!

Outside of the test cabinet construction, I received my 4x8 sheet of quartersawn curly maple veneer from Veneersupplies.com (Thanks Joe!). The wood is beautiful on its own, and I can't wait to get a bit further along in the project to start some test panels for finishing

Since I have an actual slot port to play with now, I figured It was time to take an initial swipe at the cabinet port tuning. One wall of the cabinet is yet to be glued on and flush trimmed, so this helped the process a lot. I used 1" thick quote "project foam" from Walmart to line the walls of the ported enclosure, since I modeled my enclosure that way in Bass Box. I mounted the Dayton Esoteric woofer with the machine screws, as planned. Only one of my threaded inserts was a bit off-kilter, but I'm not 100% sure how that happened. Regardless, I'll have to remove that insert, glue some kind of dowel pin plug into that hole, and try again with a fresh drilled hole. This is why you can see 5 screws and one blob of 3M poster tack on the woofer.

BassBox had my cabinet predicted at an Fb of 31.18 Hz based on a 4" x 3/4" x ~11" slot port, flares on both ends, and 0.65 ft^3 of internal volume. DATS V2 measured my Fb at 28.9 Hz (granted this was with only one flared entrance (inside). Not too shabby for a first crack. I took two measurements in DATS. One has only four clamps holding the cabinet together, and the other has six. I'm not pretending this is perfect... in fact there's probably a good few places for air to leak out of this setup. Unfortunately there's no good way to tune this kind of slot port arrangement without gluing both the port and the wall to the cabinet.

In order to fine tune these Fb results, I will take a little length off the internal slot port tunnel. I plugged the current 28.9 Hz Fb value into BassBox to see the impact, and it predicted 0.5 dB less output between ~50 and 100 Hz. Possibly not noticeable, but that would also have me approaching xmax sooner, and I'd rather not go there. Once the final length has been established, I'll cut the other two port tunnels to that length and move forward. Getting closer and closer to crossover time!

[jhollander]

Keith how are you adding the veneer to the box? I've been spending some time at Joe Woodworker so I'm thinking about building a bag and vacuum bagging my veneer on the box.

[KEtheredge87]

Keith how are you adding the veneer to the box? I've been spending some time at Joe Woodworker so I'm thinking about building a bag and vacuum bagging my veneer on the box.

Hi John, The short answer is by using an iron-on method with paper backed veneer and the heat lock glue that Joe sells. However... I can't seem to make anything simple, so get a load of this complicated mess I'm planning.

For my heat lock veneer shenanigans....

Part 1 - Wrap the front, top, rear, and bottom with one long sheet of veneer that's 1/8" to 3/16" wider than necessary. I plan to cut 1/8" deep x 1/4" wide slots around the perimeter on each edge of the veneer with a slotting cutter and an obscenely large diameter router bit bearing. To avoid chip out on the veneer, I intend to climb cut this so the slot cutter blades are always slicing down from the top of the veneer instead of pushing fibers away from the cabinet like I would get with a conventional / push cut.

Part 2 - For the side panels, I will again place a 1/8" - 3/16" oversized square of material on the side panel. I will make an MDF template with side walls that fits snugly against the cabinet to make sure I'm in a consistent location when the tool gets used on each side of the cabinet. From there, I'll use a template bushing and a down cut spiral bit to carve a 1/4"x 1/8" groove into the side panels to trim away excess veneer and give me the design aesthetic I'm after.

Part 3 - Painting. Once I have all the veneer in place, I'm going to meticulously mask it off with delicate surface frog tape (the yellow stuff) and try to get some black automotive spray paint on the exposed MDF edges.

Part 4 - Veneer finishing. I plan to do some fancy dye work like the curly maple finishes video from Woodworkers Source on Youtube. I love the way that Mark puts his videos together, and I've never had a finish turn out badly following his recommended methods!

Assuming I don't screw all of this up... I'll end up with something like the Fusion360 renderings I made earlier in this project. Fingers (and eyes and toes) crossed!

Finally, on the topic of vacuum bagging. I have only used paper backed veneer with heat lock thus far in my speaker building career, but I have done several vacuum bagged carbon fiber composite panels in grad school, so I'm generally familiar with the processes that Joe lines out on his website. The technique really isn't hard to do if you've got the right equipment. Lots of fancy breather cloth, platens, valves, vacuum bag tapes, and then the bagging material itself. Perhaps the process doesn't really require all the trimmings that funded research can afford you

[KEtheredge87]

Evening everyone!

A simple update for this evening. I took my test cabinet slot port back to the table saw and trimmed ~1/8" off to adjust the Fb I was measuring. That ended up raising my Fb to 30.95 Hz, which is plenty close enough for me (and probably waaaay close enough for the not-so-anal among us) to the BB6 models. Final slot length is 11 3/8" for the slot section inside the cabinet, overall length of ~12 3/4" when you add the 1 1/4" thick front baffle.



What I would really like to test before I go much farther is whether I will get any port noise out of this setup. I have no XO filters assembled for this speaker yet, but I can probably slap an inductor coil in series with the woofer just to give me a low pass. Just need to run some bass through it to see if I get any nasty chuffing noises from the port. The port itself has a smallish internal flare with the 1/4" roundover I applied, and I have intended on routing a similar roundover on the front of the cabinet after veneering. BUT... that is pending an experiment with paper backed veneer and roundover bits. If adding a roundover to an edge like that results in a ratty looking seam, or a bunch of tearout, I'd be required to keep the cabinet as a flush port on the front.

Does anyone have any thoughts, concerns, or ideas on testing that port before getting any more committed? I can still re-hash things a bit if need be. I haven't glued together the other ports, or cut any slots in the other front baffles. Now would be the time

Thanks for following along

[4thtry]

I usually load my box alignment and port dimensions into WinISD and then test this using the velocity tab. If the port air speed is 50mph or less with about 40 to 50 watts applied, I figure that I am OK

[Kevin K.]

Evening everyone!

Does anyone have any thoughts, concerns, or ideas on testing that port before getting any more committed? I can still re-hash things a bit if need be. I haven't glued together the other ports, or cut any slots in the other front baffles. Now would be the time

Thanks for following along

Keith, it would be a shame to veneer the entire cabinet and then try the roundover on the port only to find out you don't like the end result. Seems you have more than enough veneer, cut a slot in a piece of scrap, cover it in veneer and then try the roundover to see if it's turns out the way you want it to.

I didn't go back and look at the BB plots, were you marginal on the velocity and that's what has you concerned?

[KEtheredge87]

I usually load my box alignment and port dimensions into WinISD and then test this using the velocity tab. If the port air speed is 50mph or less with about 40 to 50 watts applied, I figure that I am OK

Keith, it would be a shame to veneer the entire cabinet and then try the roundover on the port only to find out you don't like the end result. Seems you have more than enough veneer, cut a slot in a piece of scrap, cover it in veneer and then try the roundover to see if it's turns out the way you want it to.

I didn't go back and look at the BB plots, were you marginal on the velocity and that's what has you concerned?

Thanks Bill and Kevin,

I hadn't posted any BB6 plots yet since I was too busy fiddling around with wood glue and DATS. My only real (and likely unfounded) concern is this project is the first slot port I've ever designed. My readings on this forum have me thinking these are somehow more difficult and/or prone to port noise if done incorrectly. The BB6 plots attached below suggest that I am fine with my current arrangement. Xmax for this driver would be breached after ~50 watts, and the RMS power handling is 100W, so I'm in fine shape there Even bumping things up to xmax + 10% only lands me at 60 watts. The port velocity for my 12.75" long x 4" wide x 3/4" high port never exceeds 21 m/s under a 50 watt load. More than anything... I just sweat the details to a fault!

On the veneer then round-over idea, I will absolutely test this on a scrap piece first. Honestly, The bassbox model now only has one flush end included (in my case... the interior end of the port) and it's darn near spot on with the impedance measurement I took yesterday. If the experiment proves to be a bad idea, I'll post it for learning here, and go with a flush end facing out. No reason to ruin the project!

Thanks for the prod to give myself an (in)sanity check! Back to wood glue!

[KEtheredge87]

Bit more gluing done tonight, as well as some custom dremel work. One thing I noticed last night with the test cabinet was that the Esoteric driver has it's solder tabs connected to a spoke on the cast frame. Just so happens that spoke is also in line with one of the mounting holes on the flange. Which of course, means that the solder tabs are nearly interfering with the front baffle and are not sitting in one of the relief chamfers like I was planning. See Bill, 4thtry , I'm still leading the way with my mistakes . Since I have threaded inserts in those areas, I used a sanding drum on my dremel to knock back a little bit of the MDF on those spots. I didn't go too deep, so I shouldn't compromise the threaded insert while giving a little bit of clearance to the tabs and solder beads where the tinsel connects.

After the dremel work, It was time to make a glue mess. I assembled the two other slot ports and put together cabinet 2 of 3's front / back / top / bottom. Good thing I found a few more clamps in my not-so-organized garage near the scrap MDF section! I want to get these cabinets as close to final cuts as possible as soon as I can so the joint lines that will get veneered or painted have some time to expand. Not only that... but that means I'll be getting into the XO phase of the project! I have so much to learn and experiment with there, starting with simply taking good measurements of a coaxial driver in my cabinet!

Thanks again for following along!

[4thtry]

. . . . See Bill, 4thtry , I'm still leading the way with my mistakes . Since I have threaded inserts in those areas, I used a sanding drum on my dremel to knock back a little bit of the MDF on those spots. I didn't go too deep, so I shouldn't compromise the threaded insert while giving a little bit of clearance to the tabs and solder beads where the tinsel connects.


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Nice recovery! Your mistake has now become an innovative mounting technique!