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  • DIY Measuring Mic

    While shopping on Digikey for an amplifier part, I came upon several interesting mic capsules, so I bought a few CMA-4544, and embarked on the task to see if I can produce a cheap measuring mic as a back up for my Dayton EMM6. Supplies used:

    - Male XLR connector n($3.00)
    - Aluminum tubing from hobby shop ($2.00)
    - Shielded microphone wire ($0.69/foot)

    The microphone wire is soldered to the mic capsule with the proper polarity, then connected to the XLR connector. Pin 1 and 3 of the XLR are connected together. After firing up ARTA, I then calibrated the sound card, then did a gated impulse measurement of a tweeter using the EMM6 with the calibration file loaded. The resulting FR is then exported to a CSV file. I then performed the same procedure with the CMS-4544 mic, and exported the data to another CSV file. I then recorded the difference in magnitude between the two files, and used this as the calibration file for the CMA-4544. I'm excited that the measurements came out pretty close, but please realize that I'm performing this DIY task with a nursing background. Please take a look at the resulting measurements and let me know if I have case here. I still have to fine tune the calibration file, may be do a cal file for woofers and tweeter separately, but I think if my EMM6 is screwed up in any way, I can use this back up mic. What do you think?

    Hong
    Attached Files
    Some people are addicted to Vicodin. I'm addicted to speaker building.

    The Chorales - Usher 8945A/Vifa XT25TG Build
    ESP Project 101 Lateral MOSFET Amplifier
    LM4780 Parallel Chipamp
    Sonata Soundbar Project
    The Renditions - Active/Passive Towers

  • #2
    Re: DIY Measuring Mic

    It's a great idea. I've done similar things, although not nearly as tidy as you have. The problem with those little capsules IME (I used the Panasonic WM61A that so many other people use) is that they tend to give "noisy" measurements. You can really see it in the impulse responses. Not a major deal unless you're trying to capture low level information. For back up or room measurement, sure, for serious measurements, maybe not.
    https://www.youtube.com/channel/UCm2...oSKdB448TTVEnQ

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    • #3
      Re: DIY Measuring Mic

      Nice job!

      Comment


      • #4
        Re: DIY Measuring Mic

        So it would appear that the EMM6 uses the CMA-4544 capsule? How does it compare to the WM61A noise floor wise and can the WM61A be improved in anyway so it isn't as noisy or are we left with how it came from the factory? Also is anyone doing calibration services for home made measurement mics? Anyone have experience with sending off mics for calibration and the cost?

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        • #5
          Re: DIY Measuring Mic

          Have you seen Linkwitz' article on modifying microphone capsules?

          http://www.linkwitzlab.com/sys_test.htm#Mic
          Attached Files

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          • #6
            Re: DIY Measuring Mic

            Yes i have but doesn't that just improve the maximum SPL and lower the distortion for a given SPL? I didn't see any info that it improved the noise factor.

            Comment


            • #7
              Re: DIY Measuring Mic

              Originally posted by Dave Long View Post
              Yes i have but doesn't that just improve the maximum SPL and lower the distortion for a given SPL? I didn't see any info that it improved the noise factor.
              I dunno, I haven't actually read the entire article, but Linkwitz is a smart cookie.

              Comment


              • #8
                Re: DIY Measuring Mic

                Originally posted by Dave Long View Post
                Also is anyone doing calibration services for home made measurement mics? Anyone have experience with sending off mics for calibration and the cost?
                Note sure he's still doing calibrations, but he sure used to.
                http://www.cross-spectrum.com/
                http://www.hometheatershack.com/foru...rophone-calibr
                Live in Southern N.E.? check out the CT Audio Society web site.

                Comment


                • #9
                  Re: DIY Measuring Mic

                  He still does. You can buy a Dayton mic from him, pre calibrated, or send your own in. He charges $50 including shipping for cal, $75 for the Dayton Emm-6.

                  Originally posted by carlspeak View Post
                  Note sure he's still doing calibrations, but he sure used to.
                  http://www.cross-spectrum.com/
                  http://www.hometheatershack.com/foru...rophone-calibr
                  Some people are addicted to Vicodin. I'm addicted to speaker building.

                  The Chorales - Usher 8945A/Vifa XT25TG Build
                  ESP Project 101 Lateral MOSFET Amplifier
                  LM4780 Parallel Chipamp
                  Sonata Soundbar Project
                  The Renditions - Active/Passive Towers

                  Comment


                  • #10
                    Re: DIY Measuring Mic

                    Originally posted by hongrn View Post
                    He still does. You can buy a Dayton mic from him, pre calibrated, or send your own in. He charges $50 including shipping for cal, $75 for the Dayton Emm-6.
                    That's good news. I was somewhat doubtful he was still doing it because his home page doesn't even mention doing calibrations nor, is a direct link I had to his calibration page work any more.
                    Live in Southern N.E.? check out the CT Audio Society web site.

                    Comment


                    • #11
                      Re: DIY Measuring Mic

                      I just got a Product End of Life notification from DigiKey the other day about the WM-61A capsule. I think August 1st is the last day to order them. I'll check when I am at work on Tuesday.

                      Marc

                      Just checked DigiKey. Listed as Obsolete now, and the have zero in stock, so I guess they are gone, unless you find them somewhere else.
                      Last edited by msibilia; 05-26-2013, 11:09 AM. Reason: addl info

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                      • #12
                        Re: DIY Measuring Mic

                        Maybe eBay. I got a dozen on there a long time ago. I've lost them though.

                        Getting one of the new USB mics is worth it. Unless you're really on a budget.
                        https://www.youtube.com/channel/UCm2...oSKdB448TTVEnQ

                        Comment


                        • #13
                          Re: DIY Measuring Mic

                          Originally posted by ryanbouma View Post
                          Unless you're really on a budget.
                          I are.

                          I found this: http://www.jlielectronics.com/products/JLI%252d61A.html
                          and I thought it could be used with the Linkwitz mod. The values are all about the same.
                          But if the consensus view is that these are not suitable for speaker design, I may skip it.
                          On the other hand, even if it's not ideal, perhaps it's good enough to get me by until I can save up for the usb mic?
                          All I really need right now is something to take some room measurements, and start getting familiar with the software for measuring drivers. By the time I'm ready to really start designing something, I should be able to spring for a better mic.

                          But if anyone knows of another diy mic plan that works better, maybe with a better capsule, that would be sweet! :-D
                          Nonsense. You're only saying that because no one ever has.
                          Tarkus of Egypt

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                          • #14
                            Re: DIY Measuring Mic

                            Hong, really nice job, you even got the look the same... but most importantly, the result is pretty flat.
                            Might not be too hard to derive a Cal file from your EMM-6. It's so close, it hardly needs it, though...

                            Other comments to other comments...


                            This capsule being a good choice is likely... but remember that they won't always be the same... I think Herb at Cross Spectrum has it, but theres a graph with 20 or so WM-60 capsules showing how much they can vary. Point is, you never are sure, unless you measure...


                            Sad to hear about the WM-61 exiting production... it was a nearly as good alternative to the -60 when it went away. Good that Hong's discovery looks worthy. Lots of similar mics out there, that roll off purposely around 100hz to make better voice mics.


                            And, finally (man, typing with thumbs on a tablet sucks) I'd wonder if the Linkwitz mod could work on other capsules, not that it couldn't electrically, but other capsules might not allow you to easily access the neccicary points like the -60 ( and -61?) does, as Sigfried found. Could be... might have to hack a few open to figure that out...

                            Comment


                            • #15
                              Re: DIY Measuring Mic

                              Audessey mics that come with AVRs test out amazing close to my calibrated EMM-6. I can't say for every brand, but the one with my Denon reads well, and one from a Yamaha read well. I think those little mics are pretty well consistent from brand to brand, so that may be an option.

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