How to Build a Cheap and Easy Measurement Rig

Discussion in 'Measurement Setups, Systems, and Standards' started by OJneg, Feb 28, 2016.

  1. OJneg

    OJneg The Most Insufferable

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    The thing on the left is the mic, which I model as a two terminal device, red and black wire leads

    The wires that go nowhere are connected to common ground, which basically means you hook them all up together.
     
  2. spwath

    spwath Collegiate hijinks master

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    OK, great thanks, I understand it all now
     
  3. JBoogie

    JBoogie Rando

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    [​IMG]
    is this correct? just wanted to check before I solder them to the board
     
    Last edited: Aug 15, 2016
  4. OJneg

    OJneg The Most Insufferable

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    Yessir. Assuming that's a 2N5551 with the flat side up.

    Another thing to note, you can connect the "output" to either Pin 3 or Pin 2 depending on if you want positive or negative polarity. I don't recall why I specified Pin 3 as I'm not sure if the WM61's electrical output corresponds to a compressive or rarefacting wave. You guys can check that for me. :)

    Added your pic to the first post.
     
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  5. JBoogie

    JBoogie Rando

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    would soldering point to point instead of using a pcb work the same?
     
  6. OJneg

    OJneg The Most Insufferable

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    You should try to keep the layout as tight as possible. A breadboard works well like I showed.
     
  7. spwath

    spwath Collegiate hijinks master

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    Got my package, time to start building. Except I forgot an XLR connector and protoboard. And I dont have an audio interface.
     
  8. Gatucho

    Gatucho Rando

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    Hi,
    Do you have a suggestion for a replacement for the wm61 mic.the suggested at the beginning of the tread seems to have a reduced bandwidth. I can't find an authentic wm61 and others have worse specs and/or frequency response
     
  9. HappyMonkey

    HappyMonkey Acquaintance

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    thank you great thread, but i am already over my head :) can you point me out in some direction or thread where i can learn about reading measurements something like measurements and measure gear for dummies so i can catch up with many threads here on SBAF :)
    I have emu 1212m and two shure microphones and one sony shootgun camera mic would that work for measuring. Thank You
     
  10. purr1n

    purr1n Finding his inner redneck

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  11. HappyMonkey

    HappyMonkey Acquaintance

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  12. Valolilol

    Valolilol Acquaintance

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  13. HappyMonkey

    HappyMonkey Acquaintance

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  14. Kattefjaes

    Kattefjaes Mostly Harmless

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    A great thread, thanks for posting it!

    I have been having a go.. here are some terrible phone pictures...

    The circuit board:

    (Full disclosure, not my very neat layout.. someone else did a better job for me!)

    [​IMG]

    The circuit board hidden in a little bulb inline, XLR plug and mic:

    [​IMG]

    Doing a quick "how does REW work?" test.. Using firm upholstery foam, and then Creatology-style foam on top, with the mic pushed through the middle from the back. (Not pictured, large and extremely thick hardback book on the other side of the foam!):

    [​IMG]

    ..and quick and dirty output, probably with everything set wrongly, in a noisy room.. with someone asking "why does it make that noise" every time it did a sweep:

    [​IMG]

    Clearly I need to learn what the hell I am doing still, but that does look faintly like an FR.. so I am encouraged. Thanks for the thread, @OJneg!
     
    Last edited: Dec 8, 2016
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  15. Priidik

    Priidik Friend

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    I could use some consumer advice:
    Which mic pre/soundcard is good bang for buck for measurement only applications?

    Are the EMM-6 and Sonarworks mic comparable in real world quality?
    200$/€ max for mic+pre!

    Thanks ahead!
     
    Last edited: Dec 1, 2017
  16. gixxerwimp

    gixxerwimp Professional tricycle rider

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    Sorry to dig up yet another thread ...

    So I built an in-ear rig using this mic glued to the shell of a cheap IEM and the phantom power supply described here (linked to by @Serious). Got everything working with REW, but my raw measurements look a bit wonky.

    HD800 stock LR.jpg

    The peaks aren't where they should be and L/R matching is pretty off above 4k (I don't hear this listening to tone sweeps). The results were very repeatable. Hopefully this is just an artifact of my in-ear mic and L/R ear physiology, and I can just use the curves for each channel as a baseline to compare mods with. I'll measure my Clears and HD650s tonight and see if the same L/R anomalies crop up.

    Can anyone think of anything I'm doing wrong?
     
  17. spoony

    spoony Spooky

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    Yes, you are expecting the HF to behave smoothly on an ear-mounted rig.

    You could average, say, 5 measurements per ear wih slightly different headphone position each time to shift the nulls around and see if it gives a better picture. Mount the mic capsule as flush with your earhole as possible.
     
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  18. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    @gixxerwimp The phantom PSU you built, it doesn't have a compensation filter of any kind built in, does it? I'd recommend double checking that and removing if so. That HD800 doesn't look anywhere near bright enough!

    Inversely, my little phantom PSU has a measured bass roll off, found with a loopback measurement (no mic in the loop, obviously, because a DAC replaces the mic for input). I did compensate for that in measurements. It's just a limitation of the design I used and not an intended filter or anything.

    If you compensate for the overall loopback response, it should take care of frequency response anomalies in the whole chain...DAC, ADC, and phantom PSU. And, that's another thing to check, your DAC and ADC, to ensure you're getting an untainted response. Have to make sure no DSP is being applied. And it can be difficult to find a decent mic-in on many products that don't mess things up.

    Otherwise, yes, make sure that the mic essentially sits flush with the opening of your ear canal like @spoony said. Plug up that ear hole and try to keep things from protruding into the pinna. Not to mention, the closer the mic sits to the driver, likely the less treble you get.

    Physical differences between your ears will affect measurements, no doubt. The only way to account for this is to take measurements of a channel on both ears and average. Unfortunately, many headphones don't have a flat baffle/driver and won't react appropriately to being flipped like that.

    That's the main reason I often only grab a left channel measurement.

    Last thing I can think of, sometimes filters on the front of mics can be a bit too much. Sometimes you have to strip that off, the felt-like material.

    You may also have accidentally got some glue over the mics, which will dull the treble response as well. Ask me how I know that can happen. :)
     
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  19. gixxerwimp

    gixxerwimp Professional tricycle rider

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    Thanks for the input above. I followed this tutorial and it lays out how to do a loopback measurement, which I did and applied.

    Before reading your replies, I figured out the main problem was I was using James' "poor man's FD01" as an earplug because I couldn't get the mic to stick to an Etymotic silicone 3-flange (can't find my rubber ones). It was probably sticking out too far. So I switched to the Ety foam plug tip and the FR curves look a lot better. I inserted the mic so that it's about halfway between my tragus and opening of the ear canal (actually flush with the tragus if taken along the axis of insertion). I found an REW video that mentioned smoothing, so I applied some to the new measurements and they don't look too bad. Without smoothing there aren't nearly as many nulls nor are they that severe.

    My SDRs arrived yesterday and they really do tame some of the peaks. Not sure why my rig is measuring the main peak closer to 5kHz than 6kHz though.
    [​IMG]


    I don't really mind that my curves aren't comparable, as long as I can use them as a baseline to compare the results of mods. On the All SPL tab I tried the "A - B" function, but the resulting curve is most definitely not the difference in dB between the 2 curves. I also tried the "A over B" function, and it looks closer to what I would expect, but there are still some peaks/dips that have higher values than what I can eyeball from the above overlay. Am I doing something wrong?

    Edit: will post question re "main peak closer to 5kHz than 6kHz" in the HD800 thread, but assistance with the REW subtract function would be appreciated.
     
    Last edited: Mar 20, 2020
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  20. gixxerwimp

    gixxerwimp Professional tricycle rider

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    This is the schematic for the phantom power supply I built, and I used a 10uF cap, since they said in that thread that it would provide better bass response.

    Credit: Solderdude
    Mic phantom supply.png
     

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