SevenSixTwo - InDIYana 2018 Coax Design

[KEtheredge87]

I'm trying to stay generic on how to measure, and not planning on any specific values, or rolloff rate for your design. It's just an approach. I'll delete or continue at your option.

All good sir. Sounds like you got my intent. Wanted to say thanks without sounding like saying "no please go away" 😉 -- Sent from my SM-N900V using Tapatalk

[KEtheredge87]

I can help you make a x-over, but I do things a little differently than some of the other guys. I'll try not to clutter your thread, and post some ideas in this post....

Hey rpb, thanks so much for the offer! Since this particular project is competing in the InDIYana 2018 event this year, I feel like it's only sporting that I give it my best shot at designing the XO without asking for direct help on the design itself. I felt that confirming the right measurement method wasn't getting unfair help, as I imagine the resources are out there on this forum or others if I spent enough time researching.

Having said that, I do intend to post my progress along the way, and I always appreciate feedback. At this point I have some XO parts on hand from my unfinished SuperBees 2-way project, and I ran an extensive bunch of simulations in PCD with traced FRD and ZMA files a few months back before making the driver selection. As for the XO points (and if I recall correctly) I found that the Dayton Esoteric 7" woofer modeled to be very well behaved up even beyond 900 Hz, so I think I last left the XO design crossing between low and mid somewhere between 600 and 900 Hz. The Celestion coax actually has a published suggested XO design from the manufacturer that recommends an XO around 2000 Hz. They're calling for 3rd order on the HF and 2nd order on the LF parts. I think I will use that as a starting point and see what improvements or changes my setup may require.

I'm off to try and make some better measurements of the setup tonight and see what I can get accomplished! Thanks again for your willingness to help a fellow speaker nut!

[rpb]

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!

[ATTACH=CONFIG]n1365780[/ATTACH] [ATTACH=CONFIG]n1365783[/ATTACH] [ATTACH=CONFIG]n1365782[/ATTACH] [ATTACH=CONFIG]n1365781[/ATTACH]

I can help you make a x-over, but I do things a little differently than some of the other guys. I'll try not to clutter your thread, and post some ideas in this post.

Since it is so much more sensitive, measure your mid with the level turned down 20dB. Make your frd, but add back the 20dB with software.

Make a sim and measure the mid with the simmed x-over. Use the same amp setting as you used for the woofer when you measured it.

Start with very low spl sweeps, and use ear plugs in case something unexpected happens.

I usually measure from about 1m to 1.5m.

[KEtheredge87]

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

Hey wogg, Now that you mention it... you're right. That doesn't make sense.

I had to go back and re-read Jeff Bagby's white paper (yet again) to straighten myself out here. Near-field is to remove standing waves and room reflections from the measurement. In the process, that creates an upper limit to the frequency range that we can use from the near field measurement. In this case, my upper frequency would be somewhere around 800 - 850 Hz, so very far below the range that horn is supposed to handle. I suspect your list is a correct way to approach the challenge.

Also, good idea on finding a middle ground for measurement dB level. Having different input volume levels in an attempt to match output dB level felt wrong last night.

[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

[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!

[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!

[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]

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]

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 .

[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

[KEtheredge87]

Looking good!

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

[Derekj]

Looking good!

[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.

[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.