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  • #16
    Originally posted by drb View Post
    4thtry,

    Can you please point me to a location to obtain the IEC test baffle sizes?

    jhollander,

    I agree with you, my intent is to learn as much as possible and to also help with some initial baffle design and driver integration ideas before I build a baffle and mount the driver for further testing to see if my design ideas are valid. I may find that going through some of those tests are moot, but I'd like to learn what has the most value and why. I have a set of drivers that I am playing with to learn more about the measuring process and I'd like to learn as much about them and the testing methods as possible during the entire build process.

    Thanks for all the help.

    drb
    Here are a couple links to all the IEC 268-5 test baffle sizes. I am using the 200mm (8 inch) version. My overall dimensions are within 1 inch of the IEC standard, slightly modified to accomodate the 32 x 40" foam core panels that I used.

    https://www.diyaudio.com/forums/mult...imensions.html

    http://www.rjbaudio.com/Audiofiles/IEC%20baffle.jpg

    The nice thing about making an IEC test baffle is that you can "hard splice" your measurements at about 450Hz to a near-field measurement of the same driver to obtain a complete 2pi (half space) measurement from about 70Hz all the way up to 20kHz (excluding the port and deep bass measurements, which are not needed). Then you can take this 2pi measurement and correct it for baffle step and ripple using programs like the Edge, VituixCAD, BDS, the Blender, etc., to create a simulated response on a custom baffle shape. Then you can build the baffle and test to see how close your model was. The problem with using mfg's data curves is that you are never really sure if your drivers measure the same as the published ones.
    SideTowers: http://techtalk.parts-express.com/fo...corundum-build
    Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
    Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
    Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

    Comment


    • #17
      But a test baffle will tell you nothing about the real polar plot in cabinet. When I first started, I did all the pure measurement stuff, but quickly learned it was teaching me nothing. I went as far as to dig a pit to do infinite baffle of bass drivers. Useless. I tried to test woofers on a pole in the back yard but traffic noise was too high. Pretty plots don't design speakers though.

      Only the drivers in their real baffle locations, in a real box, in a real room ( minimum floor and ceiling) give you something to design a crossover from. Standards are great. It lets us read advertisements ( a.k.a spec sheet) so we can select appropriate drivers and know the baseline is the same between brands. ( but not really as there are still so many ways to lie) If I was doing evaluations of drivers, like on the ZAPH site, it provides a consistent baseline. ,

      So, the practical engineering approach I do is 1M in the middle of a room, MLS to give me the first prototype. I then build that, measure and see what I missed big. Then I go to about their in-place location which is unfortunately almost never with enough free air around them, and fine tune in place. Part of my tuning is to see if I can do anything to the room or positions instead of the crossover. Ownes Corning 705 is your friend.

      If you have an AVR with "room correction" you might do just fine doing 1M in free space. Lesson is to think about what you are doing, don't just follow some spec ( or advice including mine) without understanding if it is really helping you.

      Comment


      • #18
        I really appreciate the feedback and advice from everyone, it is all helpful and very insightful. I’m sure I will learn many of the same lessons but I hope to do so by learning from those who have trekked before me and from replicating some of the same experiments in the vein of personal experience.

        Another question: how would you perform Nearfield measurements on a driver with a phase plug, center the mic and use the math as was mentioned previously in this thread to distance the mic from the plug even though it is not the cone or dust cap?

        Thanks,

        drb

        Comment


        • #19
          Originally posted by tvrgeek View Post
          But a test baffle will tell you nothing about the real polar plot in cabinet. When I first started, I did all the pure measurement stuff, but quickly learned it was teaching me nothing. I went as far as to dig a pit to do infinite baffle of bass drivers. Useless. I tried to test woofers on a pole in the back yard but traffic noise was too high. Pretty plots don't design speakers though.

          Only the drivers in their real baffle locations, in a real box, in a real room ( minimum floor and ceiling) give you something to design a crossover from. Standards are great. It lets us read advertisements ( a.k.a spec sheet) so we can select appropriate drivers and know the baseline is the same between brands. ( but not really as there are still so many ways to lie) If I was doing evaluations of drivers, like on the ZAPH site, it provides a consistent baseline. ,

          So, the practical engineering approach I do is 1M in the middle of a room, MLS to give me the first prototype. I then build that, measure and see what I missed big. Then I go to about their in-place location which is unfortunately almost never with enough free air around them, and fine tune in place. Part of my tuning is to see if I can do anything to the room or positions instead of the crossover. Ownes Corning 705 is your friend.

          If you have an AVR with "room correction" you might do just fine doing 1M in free space. Lesson is to think about what you are doing, don't just follow some spec ( or advice including mine) without understanding if it is really helping you.
          I disagree with your comment about test baffle polar data. I have my IEC test baffle attached to a 26" high stand which is then mounted on top of my DIY polar table. I can take polar measurements in 7.5 degree increments from 0 to 90 degrees by spinning the table. (The next post in my Radiusaurus thread will show comparisons of IEC baffle verses Radiusaurus baffle verses Matrix Revolution baffle from 0-60 degrees).

          I agree with your comments of testing drivers in real baffle locations, real box, real room. That is the way I design. But I am not just following some spec. One of the main things that I am looking for in my measurements is polar plot "consistency" and how this affects the stereo imaging. Listening and measurement go hand in hand.

          Bill
          SideTowers: http://techtalk.parts-express.com/fo...corundum-build
          Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
          Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
          Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

          Comment


          • #20
            Originally posted by drb View Post
            I am entering the driver measuring arena. I have DATS V3, Omni Mic V2, and Soundeasy.

            What is the best way to capture frequency response, impulse response, CSD, etc? More specifically, how should the driver be mounted (an open baffle with a nearfield mic setup, sealed enclosure of predefined and stable volume) etc. How large should the baffle be? Can you point me to a good online resource to answer some of these questions that will come up?

            Thanks,

            drb
            drb, here is a thread that shows my step by step procedures using DATS V2, OmniMic, and XSim software. I am also a Soundeasy user, but I have not, at this point, figured out how to use it effectively with OmniMic. I think it requires a 2 channel setup with compatible soundcard to work properly.

            http://techtalk.parts-express.com/fo...hase-questions

            SideTowers: http://techtalk.parts-express.com/fo...corundum-build
            Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
            Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
            Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

            Comment


            • #21
              Originally posted by drb View Post
              I really appreciate the feedback and advice from everyone, it is all helpful and very insightful. I’m sure I will learn many of the same lessons but I hope to do so by learning from those who have trekked before me and from replicating some of the same experiments in the vein of personal experience.

              Another question: how would you perform Nearfield measurements on a driver with a phase plug, center the mic and use the math as was mentioned previously in this thread to distance the mic from the plug even though it is not the cone or dust cap?

              Thanks,

              drb
              I know you should always put the mic directly in the center of the dust cap, but I have "cheated" and moved the mic off to the side a little to see what happens. Since you have Omnimic, you can test this yourself. Plug in Omnimic and start running the sine wave sweep (track 2). Always use the "ALL" blend mode when doing near field measurements. The gating function then shuts off. Select 1/48th smoothing.

              Move the microphone tip around the phase plug by hand and watch the FR screen. You will notice that as you move closer, the overall SPL moves up and down 1 to 2dB or so. I have not noticed significant changes in the overall FR plot, but this may be due to the size and shape of the phase plug. Test and see what happens.
              SideTowers: http://techtalk.parts-express.com/fo...corundum-build
              Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
              Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
              Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

              Comment


              • #22
                Speaking of cheating, as long as I was inside the surround I got consistent results with the near field around the phase plug. Not that anyone cares but the same held true for measuring inside a horn mouth. Flying the omni mic around a speaker is one of my favorite activities...
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                Comment


                • #23
                  I am an OmniMic flyer as well. I have the mic mounted on the end of a long pole so that I can stand back and "fly" the mic through a series of 1 meter vertical and horizontal sweeps as I watch the frequency response plot continuously update on screen.
                  SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                  Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                  Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                  Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

                  Comment

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