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  • Issues using LIMP for impedance measurements...

    Okay, so I built a jig last night using 2 cables from some broken headphones, a 22ohm 1/2W resistor, and some spare 18G lamp cord. I followed the instructions, soldered everything together, and used a plastic box to house the components. I also used heat shrink to seal off the connections from one another. Now I know that the jig is wired correctly, because a continuity test between the PC OUT R channel, and the PC in L+R Channels and between these 3 channels and speaker positive is good. Also there is no continuity to ground from any of the 3 channels. Speaker negative to both PC IN+OUT ground tests good for continuity. PC OUT L channel has no continuity to any of the 3 channels or speaker connections. A measurement across PC OUT R, and PC IN R shows 22.9 ohms. across PC OUT R and PC IN L shows 2 ohms, and from PC OUT R to speaker positive shows 22.9 ohms. I can also hear the sine sweeps through the speaker when I run tests.

    Here is my issue, I can't get good measurements.

    I ran the CAL with an inductor connected, and everything looks good. Then I run a sweep, and this is what I get...



    Then I reran the CAL and it looks like this...



    So then I hooked up a speaker, ran the CAL, and ran a sweep (note I found the FIT button for magnitude on this one)...






    What am I doing wrong here?
    Attached Files
    HAGD,
    Marc

    Even though I try to tell everyone upfront, understand that I am still a Newb. I wish the status of Seasoned Veteran/Senior Member, etc. was earned with time not posts...

    TMWW thread

    Maurbacs DCR Tower

  • #2
    Re: Issues using LIMP for impedance measurements...

    I totally respect your electronics knowledge and general competence, but you must have
    messed up the jig wiring. Here's a page with a really clear diagram that helped me.
    http://zobsky.blogspot.com/2008/01/s...t-jig-for.html

    When you've got the jig right, an inductor sweep will be a simple rising curve from a flat minimum at low frequencies.
    Once that's good, you should have no problems with a real speaker.
    I don't think you want to "CAL" with an inductor in the loop. You "CAL" with a straight wire between input and output.

    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


    • #3
      Re: Issues using LIMP for impedance measurements...

      That is how it is wired. The Right PC channel is the Red wire and the Left is the White wire. I have looked it over and tested it dozens of times. PC IN L (White wire) is wired with PC OUT R (Red wire), and the resistor. Then PC IN R (Red wire) is wired with speaker positive and the other end of the resistor. Then the grounds are wired together with the Negative speaker wire. All of my testing confirms it is wired this way and that none of the wires that aren't supposed to touch are touching. I should confirm that these tests are at the points of termination, i.e. the 2 1/8" jacks, and the speaker wire ends. The tip of the jack is the left channel, middle of the jack is right channel, and base of the jack is ground.
      HAGD,
      Marc

      Even though I try to tell everyone upfront, understand that I am still a Newb. I wish the status of Seasoned Veteran/Senior Member, etc. was earned with time not posts...

      TMWW thread

      Maurbacs DCR Tower

      Comment


      • #4
        Re: Issues using LIMP for impedance measurements...

        The easiest way to find the problem will be to put the jig aside, wire with clip leads and run the tests. if you get good results, find the problem in the jig. If you don't, swap leads for PC in then PC out to make sure you are using the right ones. (that doesn't mean swap an output for an input) there is a setting somewhere in the code for which is what that must correspond to your measurement wiring. Also, your drive levels could be reduced a bit to make certain you are not actually clipping despite the indicators being green.

        Roger Hill

        Comment


        • #5
          Re: Issues using LIMP for impedance measurements...

          Marc,

          Try this jig, it's very simple and works very well for me. Good luck.
          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

          Comment


          • #6
            Re: Issues using LIMP for impedance measurements...

            Try switching the measurement channel in LIMP from Right to Left or vice-versa -
            or swap the left/right wires. I had this backwards once and got a message like:
            "non-standard inductance - check your left-right wires".

            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


            • #7
              Re: Issues using LIMP for impedance measurements...

              Originally posted by hongrn View Post
              Marc,

              Try this jig, it's very simple and works very well for me. Good luck.
              This works for me as well. Make sure to calibrate without the speaker connected.

              Comment


              • #8
                Re: Issues using LIMP for impedance measurements...

                Originally posted by hongrn View Post
                Marc,

                Try this jig, it's very simple and works very well for me. Good luck.
                Thanks hong, I will try that. I can use my M-Audio card for that type of jig too which is nice. I bought 2 100ohm 10W resistors as well, so I may use one of those in this type of jig.
                HAGD,
                Marc

                Even though I try to tell everyone upfront, understand that I am still a Newb. I wish the status of Seasoned Veteran/Senior Member, etc. was earned with time not posts...

                TMWW thread

                Maurbacs DCR Tower

                Comment


                • #9
                  Re: Issues using LIMP for impedance measurements...

                  Originally posted by donradick View Post
                  Try switching the measurement channel in LIMP from Right to Left or vice-versa -
                  or swap the left/right wires. I had this backwards once and got a message like:
                  "non-standard inductance - check your left-right wires".
                  LOL...
                  Forgot to mention I did that too... ;)
                  HAGD,
                  Marc

                  Even though I try to tell everyone upfront, understand that I am still a Newb. I wish the status of Seasoned Veteran/Senior Member, etc. was earned with time not posts...

                  TMWW thread

                  Maurbacs DCR Tower

                  Comment


                  • #10
                    Re: Issues using LIMP for impedance measurements...

                    What is your mic input setup as in windows?

                    First make sure that you have the jig plugged in and nothing attached to the measurement leads. Shorting the leads or hooking anything up will mess up your calibration.

                    Right click on the volume control (little speaker icon in the lower right corner of the screen).
                    select recording devices.
                    You should see a mic on the window that pops up with a check next to it. Double click it to open Properties.
                    Check every tab, turn off any enhancements. And under the Listen tab “listen to the device” must NOT be checked. Open the Advanced tab and change the Default Format to 2 channel.
                    Levels tab is the mic volume control. Mic Boost needs to be off.

                    Open LIMP and select generator from the setup menu. Use pink noise at 0dB and click test. Set the level using the mic level in the mic properties box you opened earlier. (BTW I run my sound output at max volume) My mic level ends up at 4%.

                    Calibrate LIMP then run LIMP. the result should be a nearly flat phase line.

                    Good luck,
                    Duane

                    Comment


                    • #11
                      Re: Issues using LIMP for impedance measurements...

                      OK I feel ignorant asking this but what exactly is LIMP?

                      Comment


                      • #12
                        Re: Issues using LIMP for impedance measurements...

                        Originally posted by skatz View Post
                        OK I feel ignorant asking this but what exactly is LIMP?
                        Loudspeaker Impedance Measurement Program.

                        Shareware, but fully functional without registration.
                        Use it to measure box tuning, Theile/Small driver parameters (good for buyouts) and lots of other stuff
                        http://www.artalabs.hr/

                        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


                        • #13
                          Re: Issues using LIMP for impedance measurements...

                          Thank you.

                          Comment


                          • #14
                            Re: Issues using LIMP for impedance measurements...

                            Nope that didn't do it either duane.
                            HAGD,
                            Marc

                            Even though I try to tell everyone upfront, understand that I am still a Newb. I wish the status of Seasoned Veteran/Senior Member, etc. was earned with time not posts...

                            TMWW thread

                            Maurbacs DCR Tower

                            Comment


                            • #15
                              Re: Issues using LIMP for impedance measurements...

                              Did you check to make sure the output format for your sound card is the same you've chosen in LIMP? For e.g., if you go to the sound control panel and check the output device, make sure it's 16-bit, 48kHz, stereo if that's what you're setting LIMP to use. Otherwise, Windows Vista onward will resample the audio to match the format you've chosen in the control panel. (In XP, the highest quality stream wins.)

                              This may not apply if LIMP uses exclusive mode.

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