SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

What's your weather like right now? Can you spray out in the yard? If it's warm enough and there's not to much wind, you've got just as good a chance of getting the paint on without debris as you do in the garage.

Hey Kevin,

Indiana has been nothing short of ridiculous for the last few weeks. Weather A.D.D. is probably an accurate statement. The next few days *might* work out OK for some outdoor spraying, it's just hard to say how windy it will really be. Every time I've tried to spray outdoors I end up waiting for a clear shot, only to have the wind kick up, reverse direction, and blow all the overspray back in my face! it's like a campfire where the smoke follows you around every time you change seats!

[Kevin K.]

Probably not ideal after looking at your forecast, think it would need to be a little warmer. John's last idea sounds feasible with a little rework to your booth, spray em from outside of it. Looks like your running out of time though and it will probably have to wait until after the event. Maybe the weather will be a little nicer the following week or weekend.

[KEtheredge87]

Hi Guys,

After lots of deliberation on my own research (and quality input from you guys), I've decided I'm going to return the cans of 2K aerospray to Eastwood and move forward with less hazardous materials for painting. While I was attracted to the stuff by the idea of better quality finishes and application methods, I had not appreciated the real health risks of using this stuff without proper (and expensive) protective equipment until recently. No speaker project is worth the health risk that's possible from messing this up even once, let alone the risks of accidental exposure to my family if someone opens a door while I'm spraying. I'll stick with enamel or lacquer based paints until I can solve the isocyanate issue at a reasonable cost.

Having said that... I was also thinking about where to stop work prior to InDIYana next week. I already had a significant amount of 3M automotive masking tape applied to the cabinets, so I went ahead and finished that masking so I can spray lacquer based black primer. This way I can try to limit possible MDF exposure to moisture or other stuff while the speakers are travelling to the show. Additionally, it will look much closer to finished, since the goal was to have these parts be painted satin black anyway. After the show I can re-mask and spray the enamel paint top-coats.

So, masking is done, and I should be able to spray in my little plastic house (I'm still chuckling over that jhollander !) this evening. A few light coats of lacquer primer will cure totally in less than 2 days, so I can paint them, epoxy the crossover carrier boards into the cabinets, wire it all up, and take some final measurements before the show.

I'm almost there, and I'm really excited! My first DIY speaker show that I'm actually competing in! This is going to be fun!!!

[Drjay]

I second the idea of not trying to get them perfect for InDIYana. Every time I have rushed a finishing job during my boat building days I've regretted it. It would probably be better to use the time to get them sounding as good as possible.

Best,
Jay

[KEtheredge87]

Good Evening Everyone,

Tonight I re-learned the obvious lesson that MDF sucks up primer, no matter how expensive the primer happens to be! I set up my painting playhouse to prime both cabinets with a single can of SEM brand 42003 black high build primer surfacer (16oz). I bought that at the auto parts store when I was still considering spraying the 2K, and the advice the car guy gave me after seeing my cabinet photos was that one can would be enough for both cabinets. Oh well. I'll buy one more can of that tomorrow and finish the spray job.

Otherwise, I can report my experiences with the paint house. For one, the overspray catcher did a fantastic job. What used to be a white filter is now covered in black overspray, just as intended. My overall construction wasn't bad, but I did pop a tape seam loose where the fan was pressed up against the intake filter. Seems I need at least 2x the outlet area as I currently have. That tent was ballooning WAY out there. Not to shabby for a $20 box fan.

Oh... and since you're reading this... it's also worth noting that I thankfully did not cause any explosions, vapor flames, or other undesirable thermal events. I started the fan before I began spraying, and I cracked both garage doors about two feet to allow fresh air to circulate. After I finished spraying, I left the booth fan on for another two hours just to let the solvents flash off and the curing process begin.

More progress tomorrow!

[tomzarbo]

Looks like it worked well... I've thought about doing something like that more to get rid of 'boogers' in the sprayed finish, but I probably never will need to as little as I spray stuff.

I'm curious though, how was the smell a few hours after you finished up? I'm thinking compared to spraying a few cans of rattle-can paint in the garage and leaving the doors open a few feet for a few hours to air stuff out...

I have a laundry room between my garage and the main house with doors on either side, so I kind of use that as a 'buffer zone' to keep fumes from entering the house by keeping both doors closed and only opening one at a time. Still smells a bit in the house, but really light... just enough to tell you sprayed something, but not enough to make your head hurt.

Nice work on everything you've been doing... I'm really looking forward to seeing these in Ohio in a few months.

TomZ

[KEtheredge87]

...I'm curious though, how was the smell a few hours after you finished up?...

Hey Tom, Thanks for following along!

Building these pop-up paint booths are always a time commitment, but I think they are definitely worth it. If nothing else, I get to avoid coating the rest of my garage in overspray! This was the first time I upgraded the design to include a positive pressure down draft system to push out the fumes. Overall the spray smell was almost unnoticeable once I removed my respirator outside of the booth. That was with the fan still running and both garage doors cracked about 2 feet. I left the fan running with cracked doors for another 2 or 3 hours before I turned it off and closed the garage for the night. This morning, I could tell some more solvents had flashed off during the overnight curing since the smell was a little stronger, but nothing like a freshly sprayed coat of paint.

I'm surprised my wife doesn't yell at me over smells more often I've been known to mix a few small batches of instant epoxy at the kitchen table before... not to mention the RTV silicone I was using at the table yesterday to seal up the coax wiring chamber. That stuff is down right acrid!

On a positive note, she told me that I've turned her into an "audio snob" since she can't stand the sound of built-in TV speakers anymore. Mission Accomplished, I say!

These guys will definitely be ready for Ohio in July. I'll be registering them for the competition shortly after the InDIYana show. See you then!

[augerpro]

On a positive note, she told me that I've turned her into an "audio snob" since she can't stand the sound of built-in TV speakers anymore. Mission Accomplished, I say!

LOL, nice...

[stephenmarklay]

Ever since getting some Kef LS50’s I have been intrigued by coaxial designs. I looked at the specs on the driver you are using and I am too much of a rookie to get a picture of how it sounds. It looks a like it has a lot of areas to tame?

Can you fill me in?

Very cool design.

[KEtheredge87]

Ever since getting some Kef LS50’s I have been intrigued by coaxial designs. I looked at the specs on the driver you are using and I am too much of a rookie to get a picture of how it sounds. It looks a like it has a lot of areas to tame?

Can you fill me in?

Very cool design.

Hi Stephen, Thanks for the compliments!

For what it's worth, I still consider myself a big-time rookie! This is only the second XO I've ever attempted myself. I didn't choose the Celestion coaxial because its' specs were awe inspiring... instead, I chose it because I was afraid that a lot of folks attending the InDIYana event would try to use the Dayton coaxials that had just come out. I wanted to ensure at least a little bit of variety

Ultimately, this driver ended up needing the hammer of THOR to make crossover that I was happy with. Celestion happens to publish a suggested 2kHz XO design on their website that goes 2nd order on the mid and 3rd order on the tweeter. I looked at this, but quickly dismissed it. Either it didn't work with my cabinet choices, or it is simply a low cost solution for a sound reinforcement scenario rather than a hi-fi audio arrangement (The Celestion brand is generally marketed toward the professional DJ/musician rather than the home hi-fi crowd, after all).

When I approached the tweeter, there were three main trouble spots that were either dealt with, or left alone. The base response ended up being a 4th order Linkwitz-Riley arrangement that actually targeted a 6th order high pass slope (-36 dB/oct... I'm going from memory here, feel free to embarrass me and check my math ) Looking at the published response graph, I planned to address the big peak at 2.5khz and the dip / peak / dip at ~11K / 15K / 18K. The big 2.5 kHz peak is some kind of resonance, since the published Fs of the compression horn tweeter is 1250 Hz. You might also notice from the mid woofer's response that there's a matching-ish suck out at the 2.5 kHz area. I believe this is a common interaction seen on coaxial drivers (no free lunch), but others might know better.

At the end of the day, I actually used 3 of 4 LCR notch filters to address my issues with this driver (hence the hammer of THOR comment). The tweeter XO on this sucker is so big I actually had to mount the midrange XO down in the woofer part of the cabinet!

If this weren't a passive XO only competition, a driver like this would really benefit from using an active crossover. Then you can boost and attenuate till you're blue in the face and have a nice flat response from a driver this squirrely.

After all the technical details, I think the driver performs quite well in my setup. Still need to actually connect two speakers at once and listen in stereo, but in mono things sound great. Heck, I've listened to my test tracks in mono so much that I'll be blown away when I get the full stereo experience again!

Hope this answers your question

[stephenmarklay]

Wow, thanks for all the detail. Ok, at least I feel a little better Super fun design. I hope it does well at InDIYana but even if it does not it is very cool. I would assume that Celestion knows a thing or two about building drivers (since Kef and Celestion are brothers of sorts.) Although, pro audio has differing requirements…

Thanks

[brkitup]

These sounding simply fantastic at InDIYana. Your hard work definitely paid off. After looking at Celestion's response graphs, though, there's no way I would have touched these with a 10 foot pole. That tweeter response is a nightmare. Nice job.

[KEtheredge87]

These sounding simply fantastic at InDIYana. Your hard work definitely paid off. After looking at Celestion's response graphs, though, there's no way I would have touched these with a 10 foot pole. That tweeter response is a nightmare. Nice job.

Hey Eric!

Thanks for the compliment I'll admit a strong bit of ignorance when I selected this driver initially. I modeled multiple simulated XO's in PCD with the Celestion driver, as well as the Morel Hybrid 524 and the Dayton CX-150. If my memory from last Oct/Nov is correct, the dayton actually simmed out the easiest to manipulate, but I wasn't sure the driver would be available in time while Dayton re-tooled the driver for noise concerns. As I said at the show, I had plenty of luck with this driver. It could have easily been a hot mess, but such is life without driver reviews to be found ANYWHERE online!

I think I'll give this driver 4 stars on PE because it DID turn out to sound very nice, but it needed a LOT of help getting there. I used 14 of 26 total XO parts just hammering this high frequency lump of coal into a diamond! In the future I'll probably not grab something so obviously meant for sound reinforcement and cram it into a Hi-Fi environment!

[howard]

Congratulations on your success at the Indiana get together.  

[KEtheredge87]

Congratulations on your success at the Indiana get together.Â*Â*

Thanks Howard!