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SevenSixTwo - InDIYana 2018 Coax Design

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  • Paul K.
    replied
    According to the Wire Table in Introduction to Electrical Engineering by Mueller I've retained from using in college over 50 years ago, 22 AWG annealed copper wire shows a resistance of 16.14 ohms per 1000 feet, so a 2-foot long piece should have a resistance of ~0.03 ohms. I would think that after you soldered your El Cheapo Amazon crimps, you would have measured a much lower value than 0.5 ohms. Regardless, the PE leads are obviously better quality (and I would solder their crimps regardless).
    Paul

    Originally posted by KEtheredge87 View Post
    Minor update - No further crossover work has been completed yet. I knew I was going to need more alligator clip test leads to cobble this XO together, so I took a chance on a 30 pack of test leads on Amazon. That didn't work out so great, as I measured the resistance of a couple once they came in. They were reading around 0.7 ohms each... which is WAY TOO MUCH in my reasoning to use in XO testing. As a frame of reference, the test leads that PE sells were thicker, on the order of 18AWG vs. the 20-22 AWG from these crazy-cheap leads. The PE test leads measured 0.03 ohms when they were only crimped, not soldered.

    As an experiment, I took one of each kind and soldered the leads to the clip. The crazy-cheapos only improved to ~0.5 ohms or so, while PE leads stayed about the same.

    Long story short, I'm ordering more of the PE test leads, which is what I should have done in the first place. We live and we learn!

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  • KEtheredge87
    replied
    Minor update - No further crossover work has been completed yet. I knew I was going to need more alligator clip test leads to cobble this XO together, so I took a chance on a 30 pack of test leads on Amazon. That didn't work out so great, as I measured the resistance of a couple once they came in. They were reading around 0.7 ohms each... which is WAY TOO MUCH in my reasoning to use in XO testing. As a frame of reference, the test leads that PE sells were thicker, on the order of 18AWG vs. the 20-22 AWG from these crazy-cheap leads. The PE test leads measured 0.03 ohms when they were only crimped, not soldered.

    As an experiment, I took one of each kind and soldered the leads to the clip. The crazy-cheapos only improved to ~0.5 ohms or so, while PE leads stayed about the same.

    Long story short, I'm ordering more of the PE test leads, which is what I should have done in the first place. We live and we learn!

    Leave a comment:


  • KEtheredge87
    replied
    Hey Javad, Thanks bud! I fully expect that there will be some tweaks after the initial setup and measure. I like the idea of using fewer resistors, as this XO is going to be crowded to say the least! At this point in my XO building career, I still like the alligator clip method for connecting parts to quickly cobble together a design. However, I don't think I have enough to do all of my XO sections at once, so I may need to order more of those! Once I feel a bit more solid in the design, I'll solder some things together.

    I did see your aluminum heat sink additions to the Pretty Persuasions' resistors, and I thought that was pretty slick! Definitely keeping that in mind for future use!

    Thanks again for following along. Hoping to get this thing cobbled together for a listen here very soon.

    Leave a comment:


  • JavadS
    replied
    Keith nice work, I've found modeling gets me a long way into the process but I always end up making changes from actual measurements with components implemented on my test board, then even after soldering everything onto the actual board I find I need to make a change or two as well, and that's not counting changes I make from listening. Point is once the modeling is finished, I might consider myself half way there generally speaking, looking forward to seeing how things progress.

    I have also had good luck with attaching small alum heat sinks to resistors to greatly increase their thermal capacity, they are cheap and available on Amazon, I use heat sink glue, see my Pretty Persuasions thread to see what I did if you missed it.

    I'll also add you can use single resistor values and measure the resistor temps once the board is done, I've found while Xsim is useful to model the resistor loads, it's not easy to estimate how much wattage a component will see, and measuring the temp once everything is soldered on the board is easy and it's also easy to add heat sinks or break into multiple components at that stage.

    Leave a comment:


  • KEtheredge87
    replied
    Originally posted by Kevin K. View Post
    Keith, it's your baby but I'd suggest trying the crossover the first time without unwinding the inductors? Especially the .27 coils, you're talking about less than a 5% change in value. Might be worth a look just to see how it actually measures.
    Hey Kevin, thanks for the suggestion. It certainly can't hurt to try it. The only reason I went this way was because of chasing very small predicted changes in PCD. We'll see how they pan out in reality before making any changes to inductor winding! I love a good science experiment.

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  • Kevin K.
    replied
    Keith, it's your baby but I'd suggest trying the crossover the first time without unwinding the inductors? Especially the .27 coils, you're talking about less than a 5% change in value. Might be worth a look just to see how it actually measures.

    Leave a comment:


  • KEtheredge87
    replied
    Whew! Alright guys... after a bit more fiddling around I am calling the prototype XO finished until listening takes place. I did some more checks on my resistor power dissipation in Xsim and found a few more places that were predicted to eat loads of power. I decided to have some fun with this and try something a little different. In order to minimize the number of places where I would need a series / parallel arrangement of padding resistors, I ordered some of the "Zister" products that have 25W ratings. This should keep the XO board a bit less cluttered while providing the power dissipation headroom that's needed.

    I have cleaned up my prototype Xsim arrangement and documented it here for grins. Once the parts come in, I also have 5 places where I needed to unwind some inductors to hit custom values. That'll be a tedious evening! I hope these sound good, since my introduction to 3-way XO's with these has been an exercise in finding a bigger hammer every time I need to change something!

    Current XO Tally sits at 30 parts / $134.35 per speaker. I'd better figure out how to make my coax chamber act like the TARDIS, as it may need to be bigger on the inside to accommodate all the electronics!

    Click image for larger version

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  • PWR RYD
    replied
    Hi Keith,
    Bring them regardless. Even if they aren't "done". After hours listening sessions are a great time to get multiple ears on them and most likely some constructive criticism and ideas.

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  • KEtheredge87
    replied
    Originally posted by PWR RYD View Post
    I look forward to hearing these at InDIYana.

    And I'm sorry if I missed it but did you finish that other project (Super Bees's?) with the Dayton NE25FW tweeters? If yes, will they be there too?
    Hey Craig,

    You haven't missed it. I got heavily side tracked into building these coaxes in time for the competition. When I last fiddled with the SuperBees, I had two versions of the XO built, but I wasn't entirely convinced I had it done. The first version had some fuzzy/boomy business going on at heavy acoustic guitar strings. The second version addressed that fairly well, but then I wasn't convinced that some tweeter distortion or some other artifacts hadn't been introduced in the process. I left some more details on what I thought I heard in that thread, as well as a youtube link to a video showing tweeter distortion that kind of sounds like what I was hearing. No one responded beyond that post (that I saw), so I haven't changed or finalized that bit yet.

    That said... I do want to bring them to InDIYana as well. Once I get the coax XO going, I'll have to devote my attention to finishing both of these up concurrently. Nearly two months to go!

    Leave a comment:


  • PWR RYD
    replied
    I look forward to hearing these at InDIYana.

    And I'm sorry if I missed it but did you finish that other project (Super Bees's?) with the Dayton NE25FW tweeters? If yes, will they be there too?

    Leave a comment:


  • jhollander
    replied
    It looks like you have extra energy above 10K both on and off axis. The 7,800 dip filled in nicely. Might try optimizing the off axis response with a slight downward tilt

    Leave a comment:


  • KEtheredge87
    replied
    Originally posted by augerpro View Post
    Did you measure at 20 or 40 degrees as suggested? How does that look?
    Hi Brandon,

    Yes. I took 20 degree off-axis measurements of the coaxial driver and ran them through the response blender. The 20 deg farfield mid-cone data got blended with the nearfield data, and the high frequency tweeter data had it's tail trimmed. I ended up with another blending anomaly though, as you can see by the odd spike in the data at 1548 Hz. The Fs of the tweeter was measured as 1196 Hz while installed in the cabinet with stuffing, so I don't think it has anything to do with that.

    Overall I don't see anything that looks like a horrible shift. The grey line in the plot shows the 20 degree of-axis response I measured, where the black line is the on-axis response. Things only dip around 2 dB or so between 3k and 6k in the off-axis measurements, and the on-axis dip at 8k looks like it filled in and went above my woofer reference line when going off-axis. In my super limited experience, I think this looks passable. Hopefully it SOUNDS passable too!

    Any other charts you'd like to see? Wasn't totally sure if there was other stuff that's common to inspect in off-axis vs. on-axis comparisons.

    Click image for larger version

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  • augerpro
    replied
    Did you measure at 20 or 40 degrees as suggested? How does that look?

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  • jhollander
    replied
    As program material is not constant I derate the wattage by 50%. If you adjust the xsim amp to a normal listening level you can derate further.

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  • KEtheredge87
    replied
    Originally posted by Paul K. View Post
    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
    Hi Paul! I don't believe in stupid questions... especially when it comes to speaker building and electronics!

    I am honestly not sure about the SPL level, but I would assume the input would be kind of transient. I'll try to explain my thoughts a bit more. I know that Xsim shows me a response level in dB on the frequency response graph's y-axis, but I don't think those values really mean anything unless I took the measurements at 1W/1m (just like the sensitivity ratings are posted on manufacturer data sheets for each driver). Ignoring whether that's right or wrong for a moment, when I set the Xsim power amplifier to 300 watts at 8 ohms, it tells me the system output is around 96 dB. It also says my power dissipated through a single 20 ohm resistor is 108 watts at 1960 Hz.

    If I think realistically, there are a few things that come to mind.
    1) I don't currently own an amplifier that can drive 300W continuously, and most amplifiers don't go there unless we're talking sound reinforcement at a club rather than enthusiast home audio.
    2) As I happen to like my ears and their ability to hear things, I wouldn't listen to it at 95 decibels all the time (or likely much ever)
    3) Music is dynamic, so even IF there were 300W outputs from the amplifier, it wouldn't be continuous, thus I could likely get by with less power handling capability for this resistor than the math would suggest.

    At the end of the day, I'm pretty sure what I have sketched up right now is gross overkill, but I don't know what the right amount of power handling and resistor load sharing is optimum either!

    Again... If I'm doing something silly, please don't hesitate to point it out. I won't learn otherwise!

    Thanks for helping me along!

    Leave a comment:

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