SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

Project is looking good man! I also wanted to try those coaxes out. I think using the same magnet for both drivers is a pretty cool idea. Hope they sound as good as they look, the FR is a bit scary looking!

Thanks man!

I'll admit I'm a bit concerned by the frequency response graphs that were published as well (Not that I have a keen eye for what to look for in those plots, my speaker building career is still young!) I did several iterations of PCD modeling to get to something that seemed like a plausible attempt at a 3-way design before deciding on the driver and placing the order.

Truth be told, my first inclination was to use the Dayton CX150, but the uncertainty in when they would be available and how they would address the design issues scared me off. Hopefully I can speed this first testing box along so I can measure with the OmniMic for my XO work. That'll be equally as exciting

[6thplanet]

Project is looking good man! I also wanted to try those coaxes out. I think using the same magnet for both drivers is a pretty cool idea. Hope they sound as good as they look, the FR is a bit scary looking!

[KEtheredge87]

Is the silicone brush used to apply glue? Great idea!
TomZ

Hey Tom, Yep! That brush was living a lonely life in our kitchen drawers, so I rescued it. The brush spreads the glue around decently, and when I'm done I just let it dry. The glue doesn't stick at all, and it just pulls out of the bristles when it dries. Pretty sure I saw the idea first from the Wood Working for Mere Mortals YouTube channel. That guy has a lot of decent practical ideas.

[tomzarbo]

Is the silicone brush used to apply glue? Great idea!
TomZ

[KEtheredge87]

Hallelujah! It looks like a box!!!!

Today I was able to finish machining the baffles and install all but ONE threaded insert... I ran out with one remaining. After that I cleaned up shop and switched to glue-up mode. I waxed a 2'x4' sheet of 1/4" hardboard to use as my glue-up surface and clamped it to my workbench (in hopes that the wax prevents any run-away glue from sticking to the table top). I did a few dry fit checks to make sure things were good. I ended up having to shave ~1/32" off my front baffle width to make it flush with the top and bottom panels. Not entirely sure why that happened since I cut all those pieces with the same fence setting on the table saw. My only guess is the front baffle MDF expanded a little bit when I made my 1.25" glue-ups. The angle of all the pieces was pretty darn square, but I wouldn't be surprised if I ended up a few tenths of a degree off. Best I can do with the tools and experience I have.

Anyway... I used as many harbor freight clamps as I could fit in there to get plenty of glue squeeze-out along my rabbet edge joints. I also did my best to clamp two speed squares into the corners to be a sort of 90 degree jig. I'll give these a good 24+ hours to set-up since there's a lot of structure depending on those glue lines in the corners. The next steps are to flush trim the edges of the front baffle to the top and bottom panels, then flush the top and bottom panel up with the back panel. A few quick router cuts there, and I can glue one oversized side wall to the whole thing and get more of a real cabinet going.

Making a speaker cabinet... one glue line at a time!

[KEtheredge87]

Hey guys, happy Saturday night!

Over the course of last night and a split work day out in the garage today, I am almost 100% done machining my other two front baffles. This time I was a bit faster thanks to the practice, and I also didn't use as many intermediate steps at the drill press to mark out my holes ahead of time. I still had to use the FTX0617 driver as my alignment tool to ensure I placed that flush mount template in the right spot, but I took a simpler approach to the Dayton driver. Rather than try and be super precise and drill holes before routing the recess (kinda silly in retrospect) I just did the router work, dropped the driver in place, and used the self centering drill bit I have for door hinges to make my centered pilot hole. I still wanted to push those pilots all the way through with a 1/16" drill bit just so I could draw some 5/8" diameter circles on the back sides as guides for use tomorrow when I cut relief chamfers. Otherwise, a 6mm drill for the 8-32 threaded inserts, and a 7mm drill for the 10-24 threaded inserts, and I'm all ready to go for tomorrow.

Aside from the front baffles, I also made a template for flush mounting the dual binding post terminal cup (PE item 260-281) on the rear panels, which worked out just OK. That terminal cup is designed with a 5mm radius on the corners, which makes my life difficult for flush mounting. Given the choice between making a template with tools and scraps I already have, or spending $20 to buy a 10mm diameter router bit, I'd just as soon save the $20. The reason this only worked "OK" was that a 5mm radius is fairly dang small! I used a 1/4" bit when making the templates, but I only have 1/2" diameter pattern / template bits, and those didn't have quite the corner following ability that was required. Ultimately, the terminal cups DO fit into the recess that was made, but it's tight, even though I used the same 1 layer of masking tape around the part when I made my template. I'm guessing that little 5mm vs. 1/2" pattern bit detail is causing some not-so-perfect fits in the corners. I'm not so concerned about that though. It's on the back, and that recess will be painted black, so there won't be an obvious flaw for folks to stare at.

For tomorrow, I'm going to cut relief chamfers, install the remaining threaded inserts, and start actual cabinet construction! Figuring out how to glue the top, bottom, front, and back together with these dados should be a small challenge. Just gotta keep it square!

[KEtheredge87]

Hey Everyone, time for tonight's installment. Today I spent more time on my test baffle re-working the woofer reliefs and giving myself a flat spot to install threaded inserts. I drilled 1/16" holes to mark the appropriate spots for the woofer mounts, then used a straight cutting bit to carve away the areas near those holes. I still have between 1/2" - 3/4" of material thickness in the spots that I machined flat, so there's plenty of MDF to support the threaded inserts and Esoteric Driver. It's also worth noting that I only had to machine flats for four of the six mounting points. I was able to use two of the original ones, that still have around 1" of thickness, so I am not concerned about the structure around the driver.

After I got that carved out, I took out the tap and die set to chase out the threads on the EZ-Lok inserts. My 3 year old bag of 8-32 inserts had some initial resistance, which tells me their zinc coating was a bit thicker. The brand new bag of 10-24 inserts had little resistance to the tap, so maybe those guys cleaned up their manufacturing tolerances! Either way you slice it... I have trust issues At least now I know the threads are clear and I won't risk pushing an insert out when I install the screws!

I'm always amazed at the amount of time it takes to design, machine, and setup a front baffle. Maybe I'm just overly careful (even when I screw things up!)

We're getting closer and closer to a glue-up on the top/bottom and front/back pieces. At least this weekend won't be finger freezing cold out in the garage!

[KEtheredge87]

I've found another way to screw up a woofer installation...
On the Tenacious Bass 8 subwoofer from last year, I realized that some woofers have different number of spokes than mounting holes.
I guess I always assumed that each mounting hole would have a basket spoke behind it, not so. There were 8 mounting holes and only 6 spokes... relieving the rear of the baffle based on the mounting holes would have been a mistake.... I realized it before I went too far, but it still surprised me!

BTW, looking good sir!

TomZ

Hey Tom, Thanks for following along! I wouldn't have thought to check the number of woofer mounting holes vs. basket spokes. I guess there's always something new to watch out for! I'm going to try re-working my test baffle to get the right clearances and bolt hole alignment tonight. Even with all the "extra" reliefs I've cut for the woofer, I still end up with the mounting tabs hitting some of the remaining MDF. Time to open things up a smidge more!

[tomzarbo]

Winner, winner, chicken dinner!

I only figured this out AFTER I dropped the Esoteric woofer into place to check the flush mount. Seems I got a bit too pencil-happy when I was making 45 deg lines with my combination square. That worked out great for the Celestion driver... but not so much for the Dayton. This baffle is still plenty serviceable, and the extra thick 1.25" baffle has enough meat on the areas that I shouldn't have chamfered to accept a standard issue wood screw no-problems.

That said.. I'm gonna have to go buy an el-basico plastic protractor from the store if I want to draw in the proper 30 degree lines on the next ones!

This is why we practice!

I've found another way to screw up a woofer installation...
On the Tenacious Bass 8 subwoofer from last year, I realized that some woofers have different number of spokes than mounting holes.
I guess I always assumed that each mounting hole would have a basket spoke behind it, not so. There were 8 mounting holes and only 6 spokes... relieving the rear of the baffle based on the mounting holes would have been a mistake.... I realized it before I went too far, but it still surprised me!

BTW, looking good sir!

TomZ

[JavadS]

Yes... much better!
[ATTACH=CONFIG]n1360676[/ATTACH]

That's how I'm doing my 8" as well, so they match horizontally

[KEtheredge87]

Just saw this too, nice job on the flush mount, nailed it! Definitely following along, can’t wait to see and hear them! Javad

Thanks Javad! Really hoping these sound good. I'm a bit nervous on the slot port as I've never done one before, but I've got the whole test cabinet to get the tuning right. I'll be getting there soon. Just gotta make more time to glue up the front / back, top / bottom, and one wall!

[JavadS]

[KEtheredge87]

Just me- but wouldn't the woofer look better with the mounts rotated 30 degrees? This way the coax and woofer both have 2 screws at top and bottom. Again- Just me...

Later,
Wolf

Yes... much better!

[KEtheredge87]

Interesting driver selection! Where did you come across the Celestions? I have a soft spot for good coaxes. I heard the TAD Model 1 a number of years at RMAF and if was a REALLY nice sounding speaker.

Thanks Brandon! It's entirely possible that one man's interesting is another man's ignorant! I came across the Celestions while perusing the PE website looking at all available coaxes for this competition project. I haven't found a single review, good or bad, and there's no real info out on the internet except for Celestion's webpage and youtube videos. I hope they turn out well! I spent a lot of time goofing around in PCD with simulated measurements trying to get a good XO design together. Once I get a test box built I can start doing some real measurements and see if I'm wildly off the mark.

As for those TAD speakers... maybe one day I'll get to hear a pair. I still get a bit sick every time I read the price tag on the TAD CE-1's at $24,000 per pair! Good lord...they'd better feed my ears grapes and waive palm branches at them for that kind of money!

[augerpro]

Interesting driver selection! Where did you come across the Celestions? I have a soft spot for good coaxes. I heard the TAD Model 1 a number of years at RMAF and if was a REALLY nice sounding speaker.