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Thread: Passive Monitor Thread

  1. #76
    Administrator Robh3606's Avatar
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    So here is a weird one. Why would you have lowered HF response measured at about and 1" from the dome than say 18" away?? And if you move out further the measurement gets rough as to be expected but HF stays??? I always though the HF were predominantly from the dome?? Guess not??

    Here take a look Red is at the dome??

    Rob
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  2. #77
    Administrator Mr. Widget's Avatar
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    When I have performed near-field woofer measurements, I typically place the mic 1/4” away from the woofer cone midway between the surround and dust cap.

    You will get a measurement that bumps up the lower bass a bit.


    Widget

  3. #78
    Senior Member Ian Mackenzie's Avatar
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    Easy.(sorry)

    At one inch you have some equidistant cancellation from other points across the surface of the dome or the cone at the location of the microphone cell.

    If you put tiny phase plug in there it would be similar to the 18 inch measurement. (this is why cone based horns have a phase plug depending on the design of the throat adapter).

    Having thought about it a bit more the large dust cap and its shape might have something to do with it.

    Looking at your graph and the calculation of 344/1600= 0.215m where 344 is the speed of sound and 0.215 metres is the wavelength at the first cancellation frequency of 1600 hertz.

    The distance at reflection is 0.1075 metres or about 4 inches.

    Looking at the dust cap if you have the mic centred there will be cancellation at reflections from points forming a circle around the mic cell.

    At reflective points closer to the mic cell you have cancellation at progressively higher frequencies.

    I think if you smooth the 18 inch measurement it will be fine.

    My tip is to try a 24 db slope to avoid break up from the 2216nd and reduce 2nd HD from the Heil.

    That will keep you occupied over the weekend.




    Ian

  4. #79
    Administrator Robh3606's Avatar
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    Thanks Guys!

    OK I will go closer and move off the dome. Give it whirl tomorrow. I am relearning LEAP forgot the sequence to load the text files for the measurement!! Oh well! I used the longer distance measurement and got what looks like a good solution in LEAP but I don't trust it. Have to do some more measurements as I am combining stuff done years ago on a different measurement system CLIO 7 vs CLIO Pocket. If this is real I am a happy camper.

    Rob
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  5. #80
    Senior Member Ian Mackenzie's Avatar
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    Nice.

    I use old measurements all the time.

    Yeah you need to have your wits about you with Leap when exporting and importing files.

    Don't forget the minimum phase transform and to change the columns for impedance.

    Its easy to screw it up.

  6. #81
    Administrator Robh3606's Avatar
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    change the columns for impedance.
    LOL bingo!!

    Rob
    "I could be arguing in my spare time"

  7. #82
    Administrator Robh3606's Avatar
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    Well did some measurements and it didn't matter where I measured or how close. Close in it rolled off! So I redid some measurements made sure all the offsets were entered properly and minimum phase transform done and it still looks good. The only way to see for sure is to get it all together and repeat the measurements from scratch. At least it seems I have a starting point. Impedance looks good. With any luck I can get a top finished before the weekend.

    Rob
    "I could be arguing in my spare time"

  8. #83
    Administrator Robh3606's Avatar
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    Been working in LEAP simplifying the parts count, adding DCR to the inductors and adjusting any series resistors as required to help compensate for any changes. It looks good still need to verify if I have the horn padded correctly and get another assembled set of measurements to do that. Tried a couple of variations on the low pass and 18db seemed to give the best solution with the measurement set I am using. Really curious how this will actually measure as it looks good on paper after doing the changes.

    Rob
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  9. #84
    Senior Member Ian Mackenzie's Avatar
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    Excellent!

  10. #85
    Administrator Robh3606's Avatar
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    Finally had some dry weather to get my horn mount boards done. It's been nuts here we had snow early Saturday morning in May!? Wake up temps today were a cool 40's with wind chill into the 30's! At least it will warm up into the 50's so I can use the table saw out back.

    Couldn't get lumber everything closed so tried to use 3/4 mdf as a brace. Couldn't pre-drill so even dead center it split Found some really nice 8' 2x4's in my local ACE that doesn't normally carry lumber. Have to trim them up a bit and use them for braces instead. Lucky I found them all the Home Depots are closed pick-up only. Crazy times!

    Rob
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  11. #86
    Senior Member srm51555's Avatar
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    Looking Nice!

  12. #87
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by srm51555 View Post
    Looking Nice!
    +1

    Watching with interest.


    Widget

  13. #88
    Senior Member Flodstroem's Avatar
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    Amazing
    Flodstroem

  14. #89
    Administrator Robh3606's Avatar
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    Thanks Guys!

    Set up a bi-amp version of the crossover. Have two measurement sets one in close the other at 4 ft. Looks good with both just some expected roll off in the last octave with distance. Going to build this first to hear how the compensation sounds on the compression driver. I already know how the woofer is. I what looks like a good solution using the 4ft measurements but don't want to pull the trigger just yet.

    Rob
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    Last edited by Robh3606; 05-23-2020 at 10:48 AM.
    "I could be arguing in my spare time"

  15. #90
    Administrator Robh3606's Avatar
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    Got really lucky had all my parts delivered yesterday before the weekend, got one built and measured. Now lets see what it sounds like! It looks close and both measurements are in the ballpark for what the sym predicted. Have to plug them in later to see how much of a delta there is.

    Rob
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