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  • Measuring Drivers Question(s)

    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

  • #2
    I'd mount it on the baffle where it will be used. The baffle makes a huge difference in response once you get any significant distance from the driver (like 1 meter, typically). If you just want to measure the raw driver, you can place the microphone about 1/4" from the cone. Like I said though, things will get very different as you move away from the cone. I haven't checked the sticky threads lately; this might be discussed there.

    If you're comparing drivers, sometimes people make a large baffle to mount the drivers, at least several feet on each edge. They place the mic close to the cone.

    In the end, one of the major functions of your crossover will be to flatten the effects of the baffle.
    Francis

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    • #3
      http://techtalk.parts-express.com/fo...driver-testing
      Francis

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      • #4
        fpitas,

        Thanks, that link is perfect.

        I am looking for a way to compare drivers and after that then I will put them in the actual baffle and measure, I was looking for creating a set of measurements that gave me a starting point.

        Thanks,

        drb

        Comment


        • #5
          Originally posted by drb View Post
          fpitas,

          Thanks, that link is perfect.

          I am looking for a way to compare drivers and after that then I will put them in the actual baffle and measure, I was looking for creating a set of measurements that gave me a starting point.

          Thanks,

          drb
          You're welcome!
          Francis

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          • #6
            I recently constructed an IEC 268-5 test baffle. I am currently using it to compare measurements of the B&G Neo3W tweeter when mounted on several different baffles shapes. There are several sizes of IEC test baffle, based on the size of woofer you want to test. I am using the one designed for 8 inch or smaller drivers.
            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

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            • #7
              On baffle measurements can mess up some of smoothest IEC measured drivers.
              John H

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

              Comment


              • #8
                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

                Comment


                • #9
                  Originally posted by drb View Post
                  fpitas,

                  Thanks, that link is perfect.

                  I am looking for a way to compare drivers and after that then I will put them in the actual baffle and measure, I was looking for creating a set of measurements that gave me a starting point.

                  Thanks,

                  drb
                  If you know the baffle size you will use, I would build something similar to the board in the link fpitas provided but the exact size of the baffle you will use with a changeable insert to swap out the drivers. Jeff Bagby's white paper on measuring in room response down to 10Hz has some good tips on measuring in general if you haven't read it.

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                  • #10
                    I totally ignore all the near-field, baffles, open space stuff. I don't use it near-field. I use the manufactures plots, a.k.a. advertisement, as enough to select the drivers. Then I build a prototype box, mount the drivers and then measure at one meter. That way, the measurements include all of the phase, offset, diffraction, and baffle step. I can use those files for simulation. As soon as I have a prototype crossover, I put them in the room and measure where I sit. Experience gives me a guide on the top end roll-off for listening position.

                    The bible for measuring is Testing Loudspeakers, by Joe D'Appoito. Old school before the great PC based stuff, but it tells you what and why. SoundEasy will do everything, but it takes quite a bit if learning.

                    Is the Omni-Mic a USB? Not sure how you do the two channel measurement to get phase and distortion due to the delays of USB mics. I use the old Berhringer mic and a Ruby mic preamp.

                    Comment


                    • #11
                      a4eaudio,

                      I missed Jeff's white paper. Thanks for linking that.

                      tvrgeek,

                      Thanks for the rundown. I have Joe D'Appolito's book, but this is the first time I actually able to measure. The Omni-Mic V2 is a USB mic. I have not measured with it yet so I cannot comment. I need to build a Soundeasy test jig and will go from there. I found Dan Nuebeck's (sp?) test jig schematic online and will order the parts to build it soon.

                      Thanks,

                      drb

                      Comment


                      • #12
                        The FREE (Tolvan's) "Edge" software (on the webs) will let you see how different sized & shaped baffles affect different size drivers (and the positioning of the drivers as well as the mic).

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                        • #13
                          Originally posted by tvrgeek View Post
                          I totally ignore all the near-field, baffles, open space stuff. I don't use it near-field. I use the manufactures plots, a.k.a. advertisement, as enough to select the drivers. Then I build a prototype box, mount the drivers and then measure at one meter. That way, the measurements include all of the phase, offset, diffraction, and baffle step. I can use those files for simulation. As soon as I have a prototype crossover, I put them in the room and measure where I sit. Experience gives me a guide on the top end roll-off for listening position.
                          This makes the most sense to me because of the reasons you stated as well as the fact that it affords one the opportunity to just build a set of cabinets to ones space limitations/desires and then simulate/prototype/test & finalize a cross-over design instead of making yourself crazy and never even starting the project and letting your speaker components sit on a shelf until you die and get sold-off at an estate sale.



                          Comment


                          • #14
                            Originally posted by Steve Lee View Post
                            This makes the most sense to me because of the reasons you stated as well as the fact that it affords one the opportunity to just build a set of cabinets to ones space limitations/desires and then simulate/prototype/test & finalize a cross-over design instead of making yourself crazy and never even starting the project and letting your speaker components sit on a shelf until you die and get sold-off at an estate sale.
                            You need to build the cabinets either way, for near- or far-field. The key distinction that I think tvrgeek is making is the difference between simulating from mfg specs vs measuring. The near-field measurement is just to get the very bottom range of the speaker, if you have confidence in the box modeling then it is really not necessary. It can be used to confirm your box modelling or if you care to show the frequency response below 300 Hz or so.

                            Measuring at the listening position is fine if that is what you are designing for. If I'm building speakers they will probably start in my family room, maybe move to my study, and then maybe end up at one of my kid's apartments.

                            Far-field: "To be in the far-field is not as far as you may think. You are effectively in the far-field when your microphone is at a distance that is 3-5 times the radiating diameter of the driver. So, for a 6.5” woofer that has a radiating diameter of approximately 5” you will be in the far-field once your mic is placed 18” or so out from the driver. In order to make sure that you are picking up the baffle step correctly you need to make sure your mic is at least twice the width of the baffle away from the speaker as well."

                            Near-field: "Near-field measurements are usually done to overcome the effects of standing waves and reflections in the room. This is accomplished by placing the microphone very close to the cone so that room and baffle effects are very low in relative amplitude compared to the impulse response, or they do not have adequate time to develop. For a near-field measurement to work correctly certain rules are usually followed: The mic needs to be placed as close to the center of the driver as possible. The mic then needs to be spaced approximately 0.10 times the effective radiating radius of the driver from the cone. So, for our 6.5” woofer, the 5” radiating diameter has a radius to 2.5”, so the mic should be positioned 0.25” (1/4”) off the dust cap."

                            [Edit: Quotes from the white paper cited in post #9]

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                            • Steve Lee
                              Steve Lee commented
                              Editing a comment
                              Good stuff, Sir! - Thanks!!

                              I do build for a specific application and if I change the application then the parts are salvaged and re-tasked.

                              My current interest is in some desktop monitors at about 3 ~ 4 feet from the skull and about 5 feet apart - clean, detailed, punchy, low volume level using a subwoofer (passive).

                          • #15
                            To add on, more measuring is good. Nearfield, farfield, and off axis help me to find issues and adjust the crossover for the best compromise. With the omni mic you can move the mic to different positions and see real time how the response changes.
                            John H

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

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