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SevenSixTwo - InDIYana 2018 Coax Design

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  • Paul K.
    replied
    Maybe this is kind of a stupid question, and I may have missed something you stated earlier, but when you're trying to determine how much power the 20-ohm resistor will be dissipating, what is the SPL level you're asking the system to generate and is it a level that's continuous or transient?
    Paul

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  • KEtheredge87
    replied
    Alright guys. I held off on ordering parts long enough to make a few tweaks to the XO. I increased the Y-axis scale until I got 1 dB per line so I could see the fine effects of changing values (FR graph attached). This allowed me to see exactly what I was changing. Unfortunately, I haven't been able to get rid of a little cancellation that PCD says is happening on my HF horn section between ~3K and 5K, but it's slight (~1/2 dB or so). I'm fine to leave this for now and measure to see what it really sounds like. (in reference to the next bit of info... I don't see the exact same amount of reverse null in XSim as I do in PCD... not sure what the difference may be. I included the acoustic offsets calculated from PCD in my XSim file)

    In order to get a handle on layout and power dissipation, I recreated my final prototype XO in the XSim program. I like to do this in order to check expected power dissipation for resistors and the power levels seen by the drivers themselves. As expected, I am having to sink off a LOT of power to bring the 103 db @ 1W/1m high frequency horn driver down to the efficiency level of the Esoteric 7 woofer. I'm having trouble deciding the most practical way to address the 20 ohm notch filter resistor that goes before the XO circuit. If I used one 20 ohm resistor, Xsim says I'd be pushing over 35W of power through that single component with a 200W power source at 4 ohm, or 70W at 8 ohms.

    I know I need to use some combination of higher power rated resistors and/or use them wired in parallel to distribute the load. The least exotic route I could think of is taking eight 40 ohm 10W dayton audio resistors and wiring them in series-parallel (two 40 ohm resistors in series x 4 banks in parallel) for an overall 20 ohm resistance. The diagram I attached shows this in the schematic, but this feels like I may be missing something.

    So... XSim experts (read: anyone else besides me!) How am I really supposed to use the power amp tuning feature in XSim? Should I set it for 4 ohms instead of 8 ohms since the minimum system impedance of this design is 4.3 ohms at 1.8 kHz? I don't really expect I'd ever put 300+ watts of amplifer power to these speakers, but I want to make sure I've spec'ed the components out safely for an XO that will get installed in a sealed chamber and covered with polyfill. Overheating resistors is a non-starter.

    Thanks in advance for any advice on using this program properly, or a smarter way to achieve the power handling and 20 ohm resistance I designed around.

    Click image for larger version

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  • KEtheredge87
    replied
    Originally posted by Kevin K. View Post
    Man you pulled that together fast! Considering what you started with, the old wise tale expression "forging diamonds from coal" comes to mind. Looking forward to seeing how the measurements come out with your crossover. Good luck!
    Thanks Kevin and Ben! I might have obsessed over this a bit this week. I'm also excited to see what can be done here. Some of those filters on the tweeter modeled as being mighty sensitive to deviations. I'm tempted to grab some of those 1% tolerance caps from Dayton on those parts. I'll finish my shopping later tonight and see what the bill comes out to be. -- Sent from my SM-N900V using Tapatalk

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  • Kevin K.
    replied
    Man you pulled that together fast! Considering what you started with, the old wise tale expression "forging diamonds from coal" comes to mind. Looking forward to seeing how the measurements come out with your crossover. Good luck!

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  • Wolf
    replied
    Very nicely done, Keith!! Looks like the tweeter did need a hammer, but you have it nailed down.

    Later,
    Wolf

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  • KEtheredge87
    replied
    Individual Sections for Prototype SevenSixTwo Coaxials XO

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  • KEtheredge87
    replied
    Hi Guys,

    I've been fiddling for a few days and I think I have arrived at a solution that's good enough to build and test. As expected, the coax gave me plenty of challenges to address. The biggest challenge actually has been the area right around 2 kHz, as that's where I've been targeting the XO for the mid cone and HF horn sections. When I put my best foot forward in terms of matching response curve to a target response in PCD, I ended up with an impedance minima around 1.8 ohms and a BIG electric phase spike up toward +60 deg. It took an extra day or two of fiddling around to get back to a passable response that kept system impedance around 5 ohms and stayed within +/- 30 degrees of electric phase. Without further ado, here's some specs and pictures!

    SevenSixTwo - Initial XO Prototype
    XO Points - 560 Hz and 2060 Hz
    Woofer to Mid - LR2 symmetric slopes
    Mid to HF - Asymmetric slopes, LR4 arrangement (HF response matched LR6 response slope, Mid response went for LR4 slope)
    Total parts count: 29 or 30 (might have missed a series resistor in the count somewhere)

    I'll be ordering parts for these tonight so I can start playing around with them soon. Hopefully I have enough space inside my Coax chamber for all these XO parts. Only 3 or 4 of these belong to the woofer!

    Let the games begin! (3-panel pictures here... individual sections next post)

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  • Wolf
    replied
    I have no doubt you'll do fine, Keith! One thing I tend to do on horns is to comp the Fs. If you get the impedance peaks out of the horn, it tends to smooth out, and then the FR bumps might not be so drastic.

    Have fun!
    Wolf

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  • JavadS
    replied
    Originally posted by KEtheredge87
    As for X-sim, yes... I like that program too. I've not played with it quite as much as I have with PCD, but I like getting a circuit layout when I'm closer to being done, as well as getting checks on estimated power through components like resistors. Javad, I also liked your recent Pretty Persuasions post about heat sinks on some of your resistors. I may need to borrow that page from your playbook, as I'm unsure how much power will need to be siphoned off to bring the coax driver down to the efficiency of the Estoeric woofer. Did you use a laser / infrared thermometer to check those surface temps?
    Keep in mind you can do all our modeling in Xsim too, you just load the FRD and ZMA files and add your components to the circuit. Yes I use a laser temp gun, works great, nice to model but nothing like some real world data.

    Oh, lastly... on the topic of driver break-in. I did hook these coax drivers up and run the midrange cone section through a sine sweep loop, going up and down from 80-100 Hz. These things only have a 2mm Xmax rating, so there wasn't a lot visually going on to confirm break-in behavior, but I gave them 8+ hours on decent volume to get the suspension moving as much as possible. Hopefully that was enough!
    I can't say my 6HX150 broke in at all, I have them crossed over around 250hz and the cone doesn't move, but I flex my driver suspensions real good when I take them out of the box and that may be all it needed.

    Also most important part...have fun! If it's not fun or you're getting frustrated, take a break and clear your head, always helps to come back fresh =)

    Javad

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  • KEtheredge87
    replied
    Thanks Kevin K. JavadS and Billet. I was always taught to play nicely with others as I grew up Making friends is a lot more fun than making folks mad anyway.

    I agree the tweeter is going to need some serious attention. The last XO simulation I did with some FRDs traced off the spec sheets was 3rd order on the tweeter with two series notch filters and some parallel resistors on that driver alone. My goal at this point is to get things reasonably flat from a simulation perspective then order whatever parts I don't already have. I've been building a small stock of XO parts from those unfinished SuperBee two way speakers, so I'll just keep adding to the parts bin as needed.Then it's just as you've said. Listen, measure, tweak, repeat until happy!

    As for X-sim, yes... I like that program too. I've not played with it quite as much as I have with PCD, but I like getting a circuit layout when I'm closer to being done, as well as getting checks on estimated power through components like resistors. Javad, I also liked your recent Pretty Persuasions post about heat sinks on some of your resistors. I may need to borrow that page from your playbook, as I'm unsure how much power will need to be siphoned off to bring the coax driver down to the efficiency of the Estoeric woofer. Did you use a laser / infrared thermometer to check those surface temps?

    Oh, lastly... on the topic of driver break-in. I did hook these coax drivers up and run the midrange cone section through a sine sweep loop, going up and down from 80-100 Hz. These things only have a 2mm Xmax rating, so there wasn't a lot visually going on to confirm break-in behavior, but I gave them 8+ hours on decent volume to get the suspension moving as much as possible. Hopefully that was enough!

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  • Billet
    replied
    You may find that they sound better than they measure. I don't think ruler flat graphs are a strength of coaxes, but they do have some other advantages in their court. I suggest starting with a simple crossover that gets the levels close and do some listening.

    The drivers probably need to break in a little (or a lot) also. I think pro drivers are stiffer and may take longer to break in.

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  • Kevin K.
    replied
    +1 to what Javad said. As for taking bites you can swallow, my suggestion would be to first focus on the tweeter since it will probably need some contouring and learn the different ways to influence it's response. A higher part count may be in order to whip it into shape but it can certainly be done. And FWIW, I'm just as green as you at this so I'm not trying to sound like I'm a know it all, just sharing from my experience of a couple of builds. The Omni-Mic is your friend and it's fun to sit down in front of a driver with a bunch of crossover components and play with all the different ways you can influence it especially when you can see and hear the differences every time a component is changed. Good Luck!

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  • JavadS
    replied
    Originally posted by KEtheredge87 View Post
    Hey Kevin, While I scoured the official contest rules portion of the InDIYana 2018 thread, I didn't see anything explicitly stating no actives. However, post #63 has Ben saying no to Actives. http://techtalk.parts-express.com/fo...97#post1338097

    I'll be interested to see what I can pull together for a passive arrangement here. I had an idea that this coax thing would be a tough nut to crack, but it remains to be seen just how tough. Judging from your response and Javad's, I might have gotten a jawbreaker instead of a nut! Oh well... this is how we learn and enjoy the challenge!
    Keith you can do it especially with the modeling tools these days, but it's going to take more time and require more complex topology than the average HiFi speaker IME, but you can do it and you'll figure it out.

    A lot of the stuff you're taking on is intimidating the first time you do it, but once you get past it, it becomes second nature and you go on to grapple with tougher concepts and techniques, I'm still learning every day I touch this stuff!

    You're dong a great job working to do this right, that's great, at the same time don't let perfection be the enemy of good, take some measurements,load them in the modeling program, see what you get, measure it, do it again, tweak and improve. I'd suggest don't get too bogged down with off axis measurements or blending and combining measurements just yet, take bites you can swallow and build off of that. You can design a very nice speaker with on axis gated 5ms measurements and not worrying too much about measuring accurately below 300hz, it's a great start and you can build from there. Also add Xsim to your modeling arsenal as it's very easy to work with and an intuitive Windows interface.

    BTW you are an incredibly gracious poster and interact with everyone so well, always a pleasure to see your humble curiosity to learn and improve more, keep it up bud!

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  • isaeagle4031
    replied
    Yeah, no active for the contest/theme portion. Just takes way to long for set-up/tear down.

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  • KEtheredge87
    replied
    Originally posted by Kevin K. View Post
    I was thinking the same thing Craig said when I saw that this morning but didn't want to rain on the parade Keith. There's always the active option and in this case it's looking like a really good option. Does the contest require passive crossovers?
    Hey Kevin, While I scoured the official contest rules portion of the InDIYana 2018 thread, I didn't see anything explicitly stating no actives. However, post #63 has Ben saying no to Actives. http://techtalk.parts-express.com/fo...97#post1338097

    I'll be interested to see what I can pull together for a passive arrangement here. I had an idea that this coax thing would be a tough nut to crack, but it remains to be seen just how tough. Judging from your response and Javad's, I might have gotten a jawbreaker instead of a nut! Oh well... this is how we learn and enjoy the challenge!

    Leave a comment:

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