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The Defiants - InDIYana 2019 Build

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  • Drjay
    replied
    Your PDF write-up is top notch as were the Defiants in real life. Thanks for posting it all.

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  • KEtheredge87
    replied
    As-expected, the PETT forum software won't allow me to post my full write-up directly because the filesize is over 2MB. Instead, I have a google drive link where you all can view my writeup by clicking below. You'll have to trust that I'm not going to rick-roll you ;)

    The Defiants - InDIYana 2019 Bare Minimum Competition - Final Writeup

    So what's next from here? I will be doing some vertical off-axis measurements to accompany the horizontal off-axis measurements that I detail in the report. I will also be doing some A-B testing with an additional 1.5ohm resistor after the 20uF capacitor in the LF circuit to control the woofer knee. I tend to like relaxed midranges, and the current 5 part XO measures much more flat than relaxed. I don't find the current XO objectionable at all with 5 parts... I just think it might be that much better with a 6th component. Time will tell.

    Otherwise, these bad boys will be going to Midwest Audio Fest in July! I hope to see you guys there!

    Thank you so much for following along with my build and learning with me. The interactions are what make the build logs all worth it.

    - Keith

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  • KEtheredge87
    replied
    Whew! After a whirlwind weekend and a great time at InDIYana 2019, it's time to update you all on the Defiants. Yes, I did finish them on-time, and yes, my crossover was pretty darn good for just 5 parts! A big thank you goes to jhollander for some help troubleshooting my XO modeling issues via email. Turns out my issue was a mislabeled tweeter ZMA file... It was right under my nose every time I opened up PCD and scrolled by the tweeter impedance plot. For future reference, tweeters are not supposed to have a double peak and tuning frequency of 38Hz! After loading a correct ZMA file all the issues went away and I had good agreement with my measurements. Speaking of which... here's some pictures of my final XO design for the competition, some measurements, and the Front Baffle reveal! Much more detail on all these topics are in my masters thesi... I mean writeup! I may have gone a bit overboard, but I do it for you guys!


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  • KEtheredge87
    replied
    A few more pictures...
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  • KEtheredge87
    replied
    Bonus post for today - Speaker Grilles!

    Normally - I hate speaker grilles. They hide the pretty drivers, generally do *something* however small to the sound we hear since they are in the way, and they're one more thing to plan for and create as part of the design.

    However, this time... with that delicate fabric dome on the RST28F sitting like a bullseye in the middle of the Visaton waveguide, I decided it was worth the effort and "insurance factor" to make it work. One day I will have kids... so grilles will be a part of life. Well... grilles and a giant safety fence between the tiny humans and the artfully designed DIY masterpieces! I'll sit back and turn the volume up and rationalize my words thinking, "Nah... that wasn't super smug of me to call my speakers DIY masterpieces on the forums so many years ago... I'm a humble guy... yeah...."

    But I digress... Let's talk about how I made grilles!

    Step 1) Design a pattern - I did this by copying the edge lines on my baffles in Fusion360 and printing it out as a template on 11" x 17" paper. Since I went this route, I also gave myself a center mark for holes cut with the router jig, and some guide lines for sanding to-the-line in the area in-between holes. This paper template was adhered to some 3/4" MDF using 3M Super77 spray adhesive, which worked great!

    Step 2) Cut the actual grille frames - I went with 1/2" baltic birch plywood for the frames because I had some extra laying around, and because I wanted the strength. There are two thinner sections in my grilles, and I wasn't sure if MDF would hold up if someone bent them just the right way to remove the grilles from the cabinet front (remember... I put some neodymium grille magnets in the cabinets to hold these). I rough cut the insides of the pieces with a jigsaw, the outside of the pieces with the bandsaw, then secured both grille blanks to the template with double sided tape. Kind of like a grille sandwich. And now Im hungry!

    Step 3) Flush cut, machine, and magnets - I used a 1/2" spiral upcut flush trim bit in my router table to remove the excess plywood and match my template shape, then I used a chamfer bit to put a 3/8" 45 deg chamfer on the outward facing edges. This made the grilles blend in with the facet-aesthetic on the cabinets pretty well in my opinion. The last part here was embedding more magnets so the grilles would be attracted to the cabinet baffles. It's important to observe polarity on these magnets so your grille actually attracts to instead of repels from the cabinet!

    Step 4) Paint it black - Since I knew I had some black "Mellowtone" speaker cloth from PE to use on this project, I used some Krylon matte black spraypaint to coat the outside of these grille frames. I didn't want the bare wood to be visible after I applied the grille cloth, which is supposed to be acoustically transparent. That also means you can see through it if you're close enough, and that bare wood would definitelly show through enough to bother me.

    Step 5) Apply fabric to the front - Again using 3M Super77 spray adhesive, I put a good layer on the outside / front facing surfaces of the grille frames, then pressed them face down on some stretched out grille cloth. This helped set the initial tack, so I could flip it over and start pulling the fabric into the corners and curves. This wasn't too difficult to do by hand, but I did use a roller to make sure everything was super smooth and adhered after I got it placed well.

    Step 6) Fold fabric around back and trim - Using one last coat of 3M Super77 with a scrap of HDF to shield most of the grille fabric on the interior, I got the backside of the grille sticky and ready to accept the grille fabric. When tacky, I folded the fabric around the backside of the grilles, which required some 45 degree cuts and seam joining. This process isn't too bad and is decently easy once you get the hang of it. After the fabric was covering all the surfaces of the grille I took an olfa razer knife and trimmed the fabric on the inside face of the interior, where the speaker cones will be. The end result is a smooth cover for the speakers that looks seamless from the front!

    I still have a little bit of bling to apply to these grilles and speaker cabinets in general... pictures of that will come later. Hope that helped!

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  • KEtheredge87
    replied
    Hey Everyone - it's been a few days so its time for another update. I had promised to post a new model result after taking more measurements and correctly processing my woofer nearfield / farfield and tweeter farfield with the Jeff and Charlie response blender program. I did give this another go... or two or three... but I still could not get things to match up with reality, so I don't know what I've done funny with that side of things. In the interest of time, I moved on to the final stretch of the project.

    Armed with OmniMic measurements that showed a good looking response curve and reverse null, and my listening interpretations of the design as-assembled, I pushed forward with orders for final XO components. I needed some 2.0 mH solid core inductors for lower DCR, some proper 20uF capacitors for the LF section, and some 15ohm resistors to triple-up in parallel (5 ohm composite) for power handling at high volumes on the HF section. I have a rough layout put together on the 3" x 5" perforated board that I selected and epoxied into the cabinet base way back on post #2, and I'm going to go vertical with the capacitors to save some real-estate. I am also glad I was able to swap a 0.15mH x 14 AWG inductor for a much smaller 18AWG version without any appreciable drop in signal, as that saved a lot of weight / a little space too.

    Tonight I'll start assembly of the XO modules and test the assembled version outside the cabinet (no more gator clips!)

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  • scottvalentin
    replied
    Great process and thanks for sharing. jhollander and rpb and PWR RYD great input!

    Always learn a lot when you guys are helping others!

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  • KEtheredge87
    replied
    Thanks again jhollander , rpb , PWR RYD , and wogg. Seems like I left the proverbial corner I put myself in, but I forgot to take off the dunce cap

    That kind of silliness will bug me, so I'll fix my mistakes later tonight/tomorrow and repost a model. One that will hopefully match my measurements better!

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  • Mountainman Bob
    replied
    Originally posted by wogg View Post

    I'm not sure you need to apply simulated baffle when you measured in far field in your step 2... but the smile test doesn't lie. These will be fun to hear!
    Listening, hearing......what novel ideas!

    Leave a comment:


  • wogg
    replied
    Originally posted by KEtheredge87 View Post
    OK... I think I did a better job of measuring my drivers and preparing for XO design. Basic steps were:

    1) Measure nearfield woofer, and farfield tweeter, farfield woofer, and farfield woofer + tweeter
    2) load woofer nearfield and farfield into blender, apply baffle diffraction, blend appropriately, extract minimum phase and export FRD
    - I picked 0.75" radius... but I don't know how that translates to a variable length facet cut.
    3) load tweeter farfield into blender, apply baffle diffraction (again with 0.75" radius), extract minimum phase and export FRD
    4) load minimum phase FRDs into PCD7, apply overlay of woofer + tweeter farfield curve
    5) set measurement distances and offsets in PCD, determine Z-offset.

    As it happens... PCD said my z-offset was literally 0.000mm

    Even after doing all that over, something still wasn't quite right, but I kinda lucked out and arrived at a solution. A pretty darn good looking solution in fact! Both Xsim and PCD are telling me my tweeter needs more padding, and that my reverse null isn't quite as sharp as the OmniMic is telling me... but this sounds really nice so far I tend to give speakers the "smile on my face" test... which is to say I tweak until I can't help but smile and think "Man that sounds good!"... and I'm smiling right now

    Assuming I make no changes to this, I think the only component robustness issue might be R2 in my tweeter... if I really wallop these guys with 100W of 4 kHz energy, XSim says that resistor will be dissipating over 50W of power. That dissipation result sounds a bit excessive to me, but I don't have any other way to estimate that currently.

    In the photos below, the Omnimic traces without reverse null have 1/6 octave smoothing applied. I did this because I read Jeff Bagby's whitepaper that states the human brain interprets frequency differences on a 1/6 octave smoothing level anyway, so that's a decent approximation for how flat I think it is by listening.

    Time for some sleep!
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    I'm not sure you need to apply simulated baffle when you measured in far field in your step 2... but the smile test doesn't lie. These will be fun to hear!

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  • wogg
    replied
    Originally posted by jhollander View Post
    Whoa, if you are using a blended woofer file the phase is not accurate and you are not using "as measured" phase. You are back to extracting minimum phase for the woofer blended file, then the tweeter, and finding the offsets. Once you extract minimum phase for the woofer you need to do that for the tweeter as well. You can't mix minimum phase with as measured phase files.

    Sounds like you may have not extracted min phase for the tweeter file.

    Also note that if you changed the measurement distance between your simulation measurements and your "with crossover" measurements the null will not be the same.
    This inadvertently really helped me out. I was stuck on using unmodified as measured files to align offsets which was throwing me off trying to get the close mic blended response to work. With this little nugget of information, I created a blended min phase response for the woofer, then just applied min phase to the tweeter and combined responses to pull into PCD.

    Thanks John!

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  • jhollander
    replied
    cross post...great minds think the same?

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  • jhollander
    replied
    Item 3 is not required, other than extracting minimum phase. Your tweeter far field measurement has the baffle in it. If you do load the the tweeter to the blender, just the trim measured tail by adjusting the LF tail, then extract minimum phase.

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  • PWR RYD
    replied
    Keith,
    In your steps 2 and 3 you state that you loaded the far field driver measurements then applied baffle diffraction. Your far field measurements already contain all the diffraction effects (assuming your measurement distance is at least two times the baffle's width). Are you adding something more to your already "good" measurements which is making them "bad"?

    The only thing I use the blender for is to "blend" the near field and far field for the woofer, and add upper and lower tails to both drivers to extend the phase response to 10 Hz and 40kHz, and to remove the room's response/noise floor from the tweeter's bottom end response. Then of course extract minimum phase for each driver.

    Leave a comment:


  • Wolf
    replied
    Looking good to me!

    I started my cabinets tonight, so I'm at least moving...
    Wolf

    Leave a comment:

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