SevenSixTwo - InDIYana 2018 Coax Design

[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.

[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]

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.

[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!

[Kevin K.]

Can't tell for sure but it looks like the bases of those stands have holes. If so, cut a couple of pieces of 3/4" mdf that are offset of the base by 2-3 inches and shoot some screws in em. Should help stabilize it until you can build the final stands.

[KEtheredge87]

Can't tell for sure but it looks like the bases of those stands have holes. If so, cut a couple of pieces of 3/4" mdf that are offset of the base by 2-3 inches and shoot some screws in em. Should help stabilize it until you can build the final stands.

Good eyes sir! Yes, those dayton stands have some spike feet that have fancy caps on the top, which is what you're seeing in the picture. I will do as you recommend to keep things from falling over!

On the final stands, I think I will install some threaded inserts on the bottom of the speaker cabinet itself to secure it to the top portion stand. Seems like making the setup one monolithic unit is the best bet for stability.

[Derekj]

Looking good!

[KEtheredge87]

Looking good!

Thanks Derek! I'm still having fun, so I must be doing something right

[Wolf]

You, Javad, Bill, and Nick are all skating way past me in terms of completion too... I haven't even started on cabs yet.

Keep up the good work!
Wolf

[1100xxben]

You, Javad, Bill, and Nick are all skating way past me in terms of completion too... I haven't even started on cabs yet.

Keep up the good work!
Wolf

I'm with you Ben. Heck, I haven't even finalized my decision on drivers .

[KEtheredge87]

Ben and Other Ben (you decide who's who ) I feel like I should have a significant slow-down as I carefully go through XO design and final cabinet finishing. I get the impression you guys are much speedier with that part since you've done this a few times. Woodworking I get... I'm still a bit low on the electron learning curve!

Thanks for the encouragement Wolf-Ben!

[1100xxben]

Originally I was planning to use that Celestion coax in my InDIYana design this year, but ended up going a different route. I'm very interested in seeing (hearing) what your end result ends up like. You've got lots of time to design/tweak your crossover.

[KEtheredge87]

Originally I was planning to use that Celestion coax in my InDIYana design this year, but ended up going a different route. I'm very interested in seeing (hearing) what your end result ends up like. You've got lots of time to design/tweak your crossover.

Hey Ben, that makes me feel a bit better about my choice of coax. When I didn't see any reviews on the PE website, hardly a mention on any forums, and little information in the rest of the internet, I started to feel like I was blazing my own trail here! The driver certainly feels solid in the hand. That magnet is a HOSS! We'll see how any of that translates into sound!

[KEtheredge87]

Alright guys... midday update. I'm finally set up for some frequency response measurements in my basement! I followed Kevin K. 's advice and made myself a bigger base for the speaker stand, which helped tremendously. I used a scrap of 3/4" Baltic Birch from my Jedi Mind Trick subwoofer project that had a bunch of jigsaw cuts and odd profile shapes already cut through it. I also took the other Dayton Audio speaker stand I had and clamped it to the big-foot version to get this speaker higher off the floor. The Coax axis (say that 5 times fast...) is a bit more than half--way between the floor and the ceiling, so I feel like that's as good as I can ask for there. I also got my shipment of Rockboard60 2" thick mineral wool slabs in yesterday, so I set 6 of those around the area to do (hopefully) something positive to the impulse response in my space. The basement is still kinda empty, so there's plenty of slap echo and sound reflection if left alone.

This leads me to the next questions in my learning journey...
A) How the heck do I record frequency responses for a three way XO design??
B) What general volume levels should I be setting when my coax has HF / LF sensitivities of 103 dB / 92 dB and my woofer has 84.8 dB? I ask because It feels like setting one common volume for all measurements would make the coax HF too loud for near field and overload the OmniMic, while the woofer's LF would be too quiet for a clean far-field measurement.

All the examples that I've seen thus far assume a two-way speaker design. Since there are no three way measurement examples I have seen, my assumption continues that the methods must scale with the number of individual drivers in use.

This is the method I have in my head, and hopefully some kind soul either confirm this or guide me to the light

01) Set up 12 uF blocking capacitor in series with the coaxial HF horn driver to roll off around 1680 Hz (Cap value = 1,000,000 / (6.2 * Cutoff freq of 1680hz * Znom of 8ohm)
02) Set up for far-field gated measurements. In this case, 20" away from a 6.5" coaxial driver (microphone in line with the coax axis)
03) Measure far-field gated midrange measurements
04) Measure far-field gated woofer measurements
05) Set up for near field measurements (about 1/4" away from the coax and woofer dust caps, respectively)
06) Measure near field coax HF horn response
07) Measure near field coax midrange response
08) Measure near field woofer response
09) Attempt to calculate Z-offset for the coax driver with Omnimic... get confused... give-up on the OmniMic guided approach and just use PCD / X-sim
10) Measure in-box impedance sweeps with DATS V2 for each driver.
11) Use response blender and baffle modeler on the midrange and woofer measurements to combine nearfield and farfield for each driver, respectively
12) Extract minimum phase for each new file
13) Finally input blended FRD files and MinPhase ZMA files to PCD for XO modeling.

Am I on the right track, or do I have something wrong? And yes, the pictures of near field and far field measurements shows that I tried some stuff last night, realized I was tired and did it wrong (gated my near field of all things ) and figured it was time to ask for help!

Thanks for any help!

[wogg]

Why would you use near field for the coax horn? I would think the files to use would be:
Far field coax horn
Far field mid, blended with near field below 300Hz
Far field woofer, blended with near field below 300Hz

Also, for level I'd measure all at the same level, and try to find a balance somewhere between the woofer being too quiet and the tweeter being too loud.
PS... not too experienced with measurements myself either, so apply grain of salt and wait for some more experienced folks to chime in