SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

Congratulations! It's been a lot of fun watching you put these together and obviously all that paid off. The get together also sounds like it was a blast.

Thanks OldBeginner! Glad you enjoy the build log process. Some days it's hard to post, but the documentation is priceless later on. The event was definitely something I'll remember for the rest of my life! Looking forward to many more! Sent from my Pixel 2 XL using Tapatalk

[KEtheredge87]

Congrats Keith, they must sound as awesome as they look! Looking forward to seeing and hearing these at MWAF.

Thanks Kevin! I'm looking forward to your thoughts on them. I thought they turned out pretty good myself, but it was more important that I hear what other folks thought of them! Steering clear of our own personal biases can be quite a challenge some days. Sent from my Pixel 2 XL using Tapatalk

[OldBeginner]

Congratulations! It's been a lot of fun watching you put these together and obviously all that paid off. The get together also sounds like it was a blast.

[Kevin K.]

Congrats Keith, they must sound as awesome as they look! Looking forward to seeing and hearing these at MWAF.

[KEtheredge87]

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

Thanks Howard!

[howard]

Congratulations on your success at the Indiana get together.  

[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!

[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.

[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

[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]

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.

[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...

[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!

[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]

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!