Need help troubleshooting my measurement rig

Discussion in 'Measurement Setups, Systems, and Standards' started by MrPhilicorda, Nov 29, 2016.

  1. MrPhilicorda

    MrPhilicorda Rando

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    First post here by a long time headphone enthusiast but a noob when it comes to measurements. I started building my own rig without that much research and now that I found this forum I've been enjoying reading about other users experiences and rigs.

    My basic design started out as a open system consisting of two plywood discs clad with 3 mm felt and held together by four wooden bars. The microphone is a t.bone SC140 small diaphragm condenser mike which supposedly has a frequency response of 20-20.000 Hz. I did some initial measurements on a pair of headphones and they looked okay when compared the Headroom graphs except for a heavy roll off in the lower frequencies. I tried different mike positions but that did not improve anything. Later made it into a semi-closed system by putting some foam inserts between the discs, but that did not improve the situation either.

    Attached below are my measurements of a pair of AKG K702 and Sennheiser HD600 that I did with the latter version of the rig. The treble and midrange looks allright but the bass drops way too quickly below 100 Hz. There should not be more than around 10 dB difference between 20 Hz & 100 Hz but with my rig there's actually around 30 dB difference.

    Anyone got a clue why is my bass response so weak?

    There are a couple of things that come to mind but since I have no real knoweledge they are just wild guesses. I'm thinking perhaps the microphone itself is to blame, perhaps it has a weak bass response. Or is it imperative to the function that the microphone sits in a sealed air tight chamber?

    The measurements:

    [​IMG]


    Here is a picture of the original design:

    [​IMG]

    [​IMG]


    And version two with the foam inserts:

    [​IMG]
     
    Last edited: Nov 30, 2016
  2. MrPhilicorda

    MrPhilicorda Rando

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    Anyone got any ideas? I'm on the verge of spending money on a new microphone but if anyone got some other ideas how to get a more accurate bass response please let me know!
     
  3. ultrabike

    ultrabike Measurbator - Admin

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    The mic tube seems a bit wide in diameter. Is that due to the width of the mic? Measurement mic capsules seem a little smaller. Maybe the answer to lack of low bass response is the tube there being too wide.
     
  4. MrPhilicorda

    MrPhilicorda Rando

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    Not quite sure I understand what you mean by "mic tube", but the diameter of the mic itself is about 20 mm. In what way does the diameter affect bass response?

    The mic I use is supposed to have a 20 Hz - 20 kHz frequency response, but how that translates into real world performance in a rig like mine I don't know.
     
    Last edited: Dec 6, 2016

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