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  • ARTA FR measurement problem

    Friends,

    I seem to have a new problem with ARTA FR measurements, I get deep nulls at 5K and 10K that aren't present in Holm measurements, so I know that my microphone (PE calibrated, never dropped) and my PC and amp are ok.

    The pics below are the same exact speaker, same microphone position, same PC. I am not concerned about the low end response, only the nulls in the high frequency response.

    Here is the ARTA FR


    Here is the HOLM FR:

    I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
    "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

    High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
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  • #2
    Re: ARTA FR measurement problem

    Never seen that happen before and I use ARTA for measuring too.
    What I do find odd about it is, the nulls are exactly an octave apart.
    To me it looks to be be more around 6k and 12k ( roughly 2.26" & 1.13").
    I mainly answered so if someone does know or you figure it out.
    I can look back at this thread if I ever have the same problems :D .
    Thanks ,
    JB

    Comment


    • #3
      Re: ARTA FR measurement problem

      Thanks - I double checked my audio setup, rebooted, etc.
      Windows 7 HP laptop with Blue Icicle used for microphone input.
      Double-checked all inputs and outputs are 16 bit 44.1 Khz.

      I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
      "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

      High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
      SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
      My Voxel min sub Yet-another-Voxel-build

      Tangband W6-sub

      Comment


      • #4
        Re: ARTA FR measurement problem

        Tell us about the geometry of the measurement setup (distances in room, to speaker, etc.), and what kind of measurement are you doing? It's helpful to know all the details explicitly. Did you happen to see my tutorial on FR measurements using ARTA?

        Easy gated impulse frequency measurements using ARTA

        I know that things (artifacts) like this happen with nearfield measurements when the distance from source to mic corresponds to some multiple of frequency or vice versa. Perhaps there is a reflection from some nearby surface causing interference?

        -Charlie
        Charlie's Audio Pages: http://audio.claub.net

        Comment


        • #5
          Re: ARTA FR measurement problem

          Originally posted by charlielaub View Post
          Tell us about the geometry of the measurement setup (distances in room, to speaker, etc.), and what kind of measurement are you doing? It's helpful to know all the details explicitly. Did you happen to see my tutorial on FR measurements using ARTA?

          Easy gated impulse frequency measurements using ARTA

          I know that things (artifacts) like this happen with nearfield measurements when the distance from source to mic corresponds to some multiple of frequency or vice versa. Perhaps there is a reflection from some nearby surface causing interference?

          -Charlie
          Charlie - you are my ARTA guru! I printed your guide about 6 months ago, and follow it religiously. Measurement was about 44 inches off the floor, and about 55 inches or so from the ceiling, and 1 meter (39 inches) on axis from the front of the woofer. I believe that I set the ARTa gating properly, just before the main reflection after the impulse. Gating time was 4.2 ms IIRC.

          This problem first surfaced a couple of weeks ago when I was re-working and measuring an old Fisher speaker. At first I thought it was specific to that speaker, then remeasured my Targas, which previously Arta measured at +- 2dB from 1K to 18K - they showed the same nulls at 6K and 12K that I'd been seeing on the Fishers.

          I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
          "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

          High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
          SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
          My Voxel min sub Yet-another-Voxel-build

          Tangband W6-sub

          Comment


          • #6
            Re: ARTA FR measurement problem

            If you're using a mic calibration file, try it without it. Maybe it got corrupted?

            TJ
            Hybrid floor stander build - The Tikki Lau - D8's

            CNC baffle cutting services

            Comment


            • #7
              Re: ARTA FR measurement problem

              Don,

              Try doing a "near-er" field measurement, e.g. only from 6 inches away or less, or a true nearfield measurement (as close to woofer dustcap apex as possible without letting dustcap contact mic when running sweep). You will be able to increase gating all the way to the end of the impulse and the FR will be immune from room responses, reflections, and so on. If the nulls have not disappeared, it's not an interference problem.

              The 6k, 12k Hz pattern does suggest interference to me, however, so that is where my money lies at this point.

              -Charlie
              Charlie's Audio Pages: http://audio.claub.net

              Comment


              • #8
                Re: ARTA FR measurement problem

                Originally posted by charlielaub View Post
                Don,

                Try doing a "near-er" field measurement, e.g. only from 6 inches away or less, or a true nearfield measurement (as close to woofer dustcap apex as possible without letting dustcap contact mic when running sweep). You will be able to increase gating all the way to the end of the impulse and the FR will be immune from room responses, reflections, and so on. If the nulls have not disappeared, it's not an interference problem.

                The 6k, 12k Hz pattern does suggest interference to me, however, so that is where my money lies at this point.

                -Charlie
                OK, thanks! It'll be a couple of days before I can mesaure again - got a crazy work schedule coming up. I'll update this thread with the new results.

                I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                My Voxel min sub Yet-another-Voxel-build

                Tangband W6-sub

                Comment


                • #9
                  Re: ARTA FR measurement problem

                  Don -

                  Are you using the same gate times for Holm and ARTA? From the graphs I'd guess the Holm graph might have smoothing (1/12, 1/6, 1/3, etc.) selected instead of "Impulse Response". Just a shot in the dark.

                  Regards....
                  "Everything is nothing without a high sound quality." (Sure Electronics)

                  Comment


                  • #10
                    Re: ARTA FR measurement problem

                    some more about the physical measurement setup.
                    I am measuring in my study, a fairly small room with an 8 foot ceiling.
                    I set the speaker on the edge of my desk and the mike about 39 inches away.
                    After a few measurements, I realized that I needed to raise the speaker so the driver under test was basically equidistant from the floor and ceiling.

                    SO... Question.

                    Choice #1 is to raise the speaker being measured by placing it on top of a utility (solid) plywood box.

                    Choice #2 is to to raise the speaker being measured by placing it on top of a small (12 inch ) table.

                    I figured that Choice 2 would be better, less reflections and better BSC measurements, so I've been using #2 for the last few months. Maybe that's the problem.

                    In a few days I'll be able to get back to this, and try with both methods, as well as Charlie's nearfield measurement check.

                    I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                    "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                    High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                    SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                    My Voxel min sub Yet-another-Voxel-build

                    Tangband W6-sub

                    Comment


                    • #11
                      Re: ARTA FR measurement problem

                      Originally posted by donradick View Post
                      some more about the physical measurement setup.
                      I am measuring in my study, a fairly small room with an 8 foot ceiling.
                      I set the speaker on the edge of my desk and the mike about 39 inches away.
                      After a few measurements, I realized that I needed to raise the speaker so the driver under test was basically equidistant from the floor and ceiling.

                      SO... Question.

                      Choice #1 is to raise the speaker being measured by placing it on top of a utility (solid) plywood box.

                      Choice #2 is to to raise the speaker being measured by placing it on top of a small (12 inch ) table.

                      I figured that Choice 2 would be better, less reflections and better BSC measurements, so I've been using #2 for the last few months. Maybe that's the problem.

                      In a few days I'll be able to get back to this, and try with both methods, as well as Charlie's nearfield measurement check.

                      I use a speaker stand, and set the stand on a small speaker box to raise it to 48" above the floor.

                      Is there a second speaker that could be getting the sweep signal as well as the one you are measuring? In HOLM, you select left or right. It's possible to select both too. Did that once by accident.

                      Also, I'm with takitaj on checking the correction file.

                      Comment


                      • #12
                        Re: ARTA FR measurement problem

                        Hi Don,
                        Just a suggestion: if you measure the speaker on a table or desk that has a solid front, you effectively increase the baffle size and increase the necessary distance to obtain a true farfield measurement. Though it is not likely the cause of your problem, it is something to consider to obtain clean measurements.

                        Jay
                        Jay
                        Our greatest glory lies not in never falling, but in rising each time we fall.

                        Comment


                        • #13
                          Re: ARTA FR measurement problem

                          Originally posted by jmb View Post
                          Hi Don,
                          Just a suggestion: if you measure the speaker on a table or desk that has a solid front, you effectively increase the baffle size and increase the necessary distance to obtain a true farfield measurement. Though it is not likely the cause of your problem, it is something to consider to obtain clean measurements.

                          Jay
                          Yah, that's why I switched the stand from a solid box to a small table - but I'm now going to go back and test the same speaker and mke distance with both type of stands, just in case there is a measurable difference.

                          I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                          "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                          High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                          SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                          My Voxel min sub Yet-another-Voxel-build

                          Tangband W6-sub

                          Comment


                          • #14
                            Re: ARTA FR measurement problem

                            I'd say it would be an idea to get a mic stand. But as said, probably not causing this problem...

                            Does ARTA have input polarity settings? Might something gotten reset?

                            Comment


                            • #15
                              Re: ARTA FR measurement problem

                              Originally posted by jonpike View Post
                              I'd say it would be an idea to get a mic stand. But as said, probably not causing this problem...

                              Does ARTA have input polarity settings? Might something gotten reset?
                              I have a mike stand, I've been talking about a speaker stand in this thread.
                              I'll be able to play with this some more Monday evening.

                              I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                              "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                              High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                              SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                              My Voxel min sub Yet-another-Voxel-build

                              Tangband W6-sub

                              Comment

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