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Acoustic center

6thplanet6thplanet
in DIY
OK guys, this is driving me nuts! Trying to find the acoustic center (Z axis). Mic is 1.45m, mic/tweeter height is 0.91m, CTC is 0.2m. I can't for whatever reason make things line up. WTF am I doing wrong here? The tweeter is cap protected with 25uF. Omnimic measurements. Is the mid being OB wacking things out? I don't remember having this issue, although this is a new room.

Comments

  • 6thplanet6thplanet
    edited April 2020
    Trying to attach measurements, thats not even working?? Does the "attach files" not work?


  • jhollanderjhollander
    edited April 2020
    Cap on the tweeter, unless you add it in your sim is messing up the match. OB could also mess it up but as long as you are at the same distance etc. for the T+ M measurement you should be good.
     John H, btw forum has decided I don't get emails
  • 6thplanet6thplanet
    Well that's what I thought. Didn't figure I needed the cap as both the individual and combined sweeps have it. I'll try it tomorrow, thanks. So what's with no file attachment?
  • jhollanderjhollander
    You should still get a match but it could be way out there, cap adds another 90 (?) degree rotation, don't recall exactly.  Flip the polarity of one of the drivers and see if you can get a match, it's not accurate. Yeah missing JB at times like this. 


     John H, btw forum has decided I don't get emails
  • dynamodynamo
    A couple thoughts: OB should not mess anything up in my experience, the cap shouldn’t mess anything up as long as it is in both measurements involving the tweeter (but I never use a cap unless it’s a true ribbon).

    Do you always use that distance? Seems far to me. With only an 8” ctc distance I’d be doing my measurements for this at about 28”. 

    Are you doing the calculations in PCD7? I know you know what you’re doing but just for a sanity check, don’t forget to adjust your measuring distance and y distance.
  • 6thplanet6thplanet
    I've tried different distance measurements, 1-2m, it is a true ribbon, PCD and XSim, tried polarity.
  • Ed_PerkinsEd_Perkins
    6thplanet said:
    Trying to attach measurements, thats not even working?? Does the "attach files" not work?


    This had me confused too. After you upload the file it will show up underneath the message box.  You then have to drag the file into the message box.  The link should then show up in the message box. At least that's what works for me.
    dcibel
  • jr@macjr@mac
    I'm talking to JP about attachments.
    I have a signature.
  • 6thplanet6thplanet
    LCY326.frd   lcy108.zma   audax326.frd   HM130Z4.zma   lcyaudax326.frd
  • 6thplanet6thplanet
    edited April 2020
    hey, i think the drag it worked?
    Also the CTC should be 0.127 (5")
  • dcibeldcibel
    The forum ruins the file name, but otherwise it works.

    Your files don't include any phase information. Check the "show phase" box in Omnimic, or extract minimum phase and try again.

    This should be obvious when you open the frd file in any old text editor. 3 columns of data are frequency, amplitude, phase. You will notice the 3rd column is empty in your files.
    I'm not deaf, I'm just not listening.
  • 6thplanet6thplanet
    LCY326.frd  audax326.frd  lcyaudax326.frd
    Should have phase now
  • 6thplanet6thplanet
    Just so you know, I can get the dip around 3K to line up 0.012 (z) seems to get close, but the big discrepancy at 1.5K is whats baffling me. Don't understand whats causing the ~10dB difference there. 
  • dcibeldcibel
    Did you try with your re-measured files that you just posted? Looks okay to me with 0.127 Y offset, -0.03 Z offset applied to the woofer.
    I'm not deaf, I'm just not listening.
  • jhollanderjhollander


    Some smoothing going on but looks good to me
     John H, btw forum has decided I don't get emails
  • 6thplanet6thplanet
    edited April 2020

    This is what I don't get. Shouldn't that also track pretty close, too? Also, I don't see how your getting  -0.03 to work without flipping polarity on the tweeter, which as far as I understand shouldn't need to happen.

  • jhollanderjhollander

     John H, btw forum has decided I don't get emails
  • jhollanderjhollander
    edited April 2020
    Your overlay looks hosed
     John H, btw forum has decided I don't get emails
  • dcibeldcibel
    edited April 2020
    The fact that you have any deviation at all between the overlay and the summed response at 20kHz is a big red flag. Were you messing with the vertical/horizontal panning buttons?

    -0.028 looks correct when I use your mic distance of 1.45m


    I'm not deaf, I'm just not listening.
  • 6thplanet6thplanet
    Ahhh, I think I see what's up, I'm not entering the CTC as negative. I'll try that when I get home.
  • dcibeldcibel
    That's not it.
    I'm not deaf, I'm just not listening.
  • 6thplanet6thplanet
    Ok, so I noticed John didn't have a value set for Relative Listening Height. With that left blank, (y axis) at -0.127, with (z) at -0.028 it lines up pretty good. That -0.028= 1.1", that seems excessive looking at the drivers overall depth. It is "acoustic center" so...??? Shouldn't there be a value for height?

     The next thing is that little spike at 1.2k, sup with that?
  • dynamodynamo
    Lines up nice now! I never enter a height
  • dcibeldcibel
    edited April 2020
    I knew you were messing with the panning buttons!

    It's relative height, not absolute. Use those values when simulating off-axis only, otherwise leave at zero so the simulation is your measurement axis.

    I posed a link to Jeff B's write up on the process in a previous post above, always good for a refresher when things aren't looking as you expect.
    I'm not deaf, I'm just not listening.
  • 6thplanet6thplanet
    Thanks for the help guys👍🏻 I knew it was something stupid, the negitive entries got me. Now to make be friends.
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