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Thread: Driver Testing Methods and Setup: Frequency Response and Harmonic Distortion

  1. #1
    Tester Extraordinaire ErinH's Avatar
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    Driver Testing Methods and Setup: Frequency Response and Harmonic Distortion

    *Mods: Please sticky this and close it. I may need to amend or add details as it's possible I've forgotten something but I will ask you about it then.

    The testing discussed here is in reference to Frequency Response and Harmonic Distortion testing done via SoundEasy.

    Setup:
    Software & Hardware:



    Baffle and Room Treatment:
    Testing is done in a 17x25 ft room, upstairs in my home away from noisy environments. The room is temperature controlled and fixed within a certain temperature range.
    The driver is attached to a 66x81" scaled model of the IEC baffle.
    This baffle is constructed of 3/4" MDF of 66x81" dimensions, with another layer of 3/4" MDF - 36x48" - on the rear. This rear layer has a 12" diameter cut out which allows for attaching the baffle inserts to the baffle. The total baffle weight is approximately 140 lbs.
    There is no obtrusion on the front of the baffle (as you may see on others' test baffle).
    Bracing on the rear was added for support. The picture below is a former model of the stand which has since been beefed up a tad with extra cross bracing. The baffle easily handles 96dB 7" driver testing sweeps at 1/2m without vibration.
    All drivers are flush mounted with a 45* chamfer on rear.



    For on and off-axis testing, I will be using a homemade jig of wood marked at 15 degree intervals and PVC cut to X length. A laser is attached to the mic boom at the back to avoid reflections so that the mic can be pointed directly at the driver's center.

    Picture:


    The room is treated with absorption panels at the 4 first reflection points: ceiling, floor, sidewalls.


    Testing Requirements:
    [INDENT]Thiele-Small & Impedance:
    • Parameters generated with woofer tester 2 automatically.
    • Impedance curve will be publushed as best can be shown to accurately read any potential blips in the response.
    • Drivers will be measured on the baffle



    Frequency Response:
    • Mic @ ~ 33"
    • Levels between 80-90dB
    • Window @ 15ms*
    • Smoothing to 1/24 unless otherwise noted
    • On Axis Testing results will be scaled to 3dB **
    • On/Off Axis Comparison Testing results will be scaled to 5dB***
    • On/Off Axis Comparison Testing will be done at 0, 15, 30, and 60 degrees.


    *This correlates with resolution down to 66hz and is allowable only due to absorption panel placement and room size.

    **3dB scaling is done so you, the viewer, can see the details of the response in close up view. I don't care that mfg's post at 5dB or 10dB scale. To me, that's of little use and one of the prime reasons I want to test drivers myself. I think it is best for everyone to see the scale in high resolution so they can see what is going on in the fundamental response.

    ***For on/off axis comparisons, scale of 5dB is used for easier viewing.


    Harmnoic Distortion:
    • Mic @ 18 inches (to help tame reflections but not clip mic input at loud levels) on axis (0 degrees)
    • SPL level at 90-95dB, depending on driver and relates to SPL @ mic distance. Level will be stated when data is posted
    • F2-F5 will be tracked
    • Window will be ~ 50hz to 20khz, where distortion will be measured from 50hz up through 12khz for all drivers, except tweeters which will start closer to 500hz (for driver protection)



    Sample Videos:

    To help you get a better understanding of the testing, here are a couple videos:
    • Frequency Response:
    • Harmonic Distortion:
    Last edited by ErinH; 05-01-2011 at 05:46 PM.
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  2. #2
    Big Daddy Chad's Avatar
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    you know that the behringer mixer has EQ correct? And said center detent on the pot is not always flat since there is no detent filter defeat?

  3. #3
    Tester Extraordinaire ErinH's Avatar
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    Setup has been calibrated L/R and there is no gain on the EQs.
    Last edited by ErinH; 04-21-2011 at 02:44 PM.
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  4. #4
    Big Daddy Chad's Avatar
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    right over your head.

  5. #5
    Tester Extraordinaire ErinH's Avatar
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    No. You're saying that the center marker on the pot isn't true center and thus could leverage on side bias against the other.
    The setup has been checked. There's only one output going to the input card which is right channel. I've checked the mixer line out in the software and gotten the same input to the soundcard on both sides of the line out. I'm good.

    As for EQ's and shit; same story. Output of mixer is dead flat going in to sound card. This mixer's pots seem to be accurate.

    Regardless, this input can be calibrated in the software. I can add some factoring in to adjust the phase should it not be good. I posted on the other site the calibration of the setup. Dead nuts flat out past 30khz with the settings on 96khz sampling. 48khz sampling; I'm good to at least 20khz which is the max of the measurement window.


    If there is something I'm still not getting, don't be an ass: call me. I'm always down to learn something.

    Edit: I still love you. But you make my fiwings hurt.
    Last edited by ErinH; 04-21-2011 at 02:51 PM.
    Your ears: The best tools you have... and they're free, too!

  6. #6
    Big Daddy Chad's Avatar
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    The pots can drift, and will on a Behringer. Mine were dead nuts flat when I got it.. not anymore. As long as you keep calibration in check you are cool.... Or... just out of curiosity..... does it have insert points (TRS) per mic input?.... you can peel a pre EQ send off of that. I end up doing that live when I can't trust the EQ on a console channel and it has no defeat.

  7. #7
    Tester Extraordinaire ErinH's Avatar
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    I believe it does.

    I'll randomly check calibration. I've got a calibration driver (an old junky cdt) to keep things in line with.
    Your ears: The best tools you have... and they're free, too!

  8. #8
    Big Daddy Chad's Avatar
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    I have an 802 also, I thought mine was smaller, it does not have inserts, but it's an older version I'm sure. I remember wanting to mod it for an insert point... if I get around to it for some reason (I really want compression on my mic) I'll document the mod.

    The insert point is the most awesomest overlooked feature in a mixer. you can do sooo much with it. Even a whole thread worth of stuff.

    For example, for an unadulterated feed right off the preamp, just use a TRS jack, wire for the send, presto! Wanna still use the channel AND have a send? Short the ring and tip, peel and stick.

    Mine only has one send, (labled FX) it's post EQ. I use mine as a mic pre and send my radio rig it's feed off the FX sens and the computer for skype and echolink off of the stereo outs.

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