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  • Need some crossover schematic interpretation

    I'm really only concerned with the midbass circuit but I don't have the knowledge to interpret it.

    For reference this is an Infinity IL60 speaker that I'm building a different cabinet for. The MB's are currently in a way small plastic chamber. Measurements show that will play down to 50Hz in a .6cf ported box and 100Hz in a sealed box about half that size. I'm considering a design that will be more optimum w/o the powered subs in the mix.

    Regarding the MB filter, I'm basically wanting to know if it affects anything on the bottom end and, if so, at what frequency?
    Attached Files
    Thanks,
    Aaron

  • #2
    Looks like there is a highpass cap of 470mF (I'm assuming mF=uF)

    I'd bet the midbass is 4ohm. Then 470mF would make for a rather typical xo point of ~85hz to handoff to the sub.

    Comment


    • #3
      Originally posted by DrewsBrews View Post
      Looks like there is a highpass cap of 470mF (I'm assuming mF=uF)

      I'd bet the midbass is 4ohm. Then 470mF would make for a rather typical xo point of ~85hz to handoff to the sub.
      Here's a pic of the WT3 sweep. R(e) is 4.3 ohms, not sure what it would be after the 2.4mH coil is inserted. I can measure the DCR of the coil later tomorrow/ Sunday if necessary.

      Some digging showed the LP crossover on the powered sub is fixed at 100Hz. The small enclosure on the MB would likely create a rise on the bottom end, a shallow filter in the range you mentioned would likely address that. These speakers are known for an impressive and arguably boringly flat response.

      If that is indeed an HP filter on th3r MB might set it up as an option for fuller range low levels minus subs with a switch for the filter for higher volumes with subs.
      Attached Files
      Thanks,
      Aaron

      Comment


      • #4
        Click image for larger version

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        This is the actual transfer fn of YOUR measured impedance on that driver (not sure if it's "free air", or "in box") acted on by your 3 element filter (assumed a DCR on the 2.4mH coil of 1 ohm - for the sake).

        The top end is rolled off by the coil / (shunt)cap combo: down -3dB around 470Hz, -6 @ 570.
        The single (large) series cap is rolling off the bottom end (F3) near 38Hz, F6 near 28Hz.

        Comment


        • #5
          Originally posted by Chris Roemer View Post
          Click image for larger version

Name:	aarondMB.jpg
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          This is the actual transfer fn of YOUR measured impedance on that driver (not sure if it's "free air", or "in box") acted on by your 3 element filter (assumed a DCR on the 2.4mH coil of 1 ohm - for the sake).

          The top end is rolled off by the coil / (shunt)cap combo: down -3dB around 470Hz, -6 @ 570.
          The single (large) series cap is rolling off the bottom end (F3) near 38Hz, F6 near 28Hz.
          Much appreciated man. The DCR of that coil does appear to be in the neighborhood of 1-1.1ohms. The sweep in the pic is free air (sitting on my dining room table actually).

          Thanks,
          Aaron

          Comment


          • #6
            The bottom-end rolloff WILL be different "in-box". The resonant "hump" should get smaller and higher in freq. in a closed box, with a ported box getting a pair of smaller humps approx. centered on the tuning freq. The filters are directly affected by the impedance values of the plot.

            Comment


            • #7
              It's important to NOTE that these are NOT plots of your bottom end responses, they just show how that single 470uF series cap affects your driver's "in-box" response. To see "how low" (F3) your woofer's response would be, you have to sim its F3 (like you say, about 100Hz in 0.3 closed cu.ft., or 50Hz in 0.6 vented) and then subtract THIS DATA from your simmed response.

              Click image for larger version

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              Purple line is the cap's effect on your closed-box response (not doing much @ 100Hz).
              The green is how that cap works on your (proposed) vented box. It does a good job around the tuning freq. ('cause the impedance is in the low "valley" there, between the humps), but has little impact at the lower imp. peak (around 40Hz), rolling off below that point. Would the -2dB "dip" from 50-60Hz be "noticeable"? That depends on a lot of other things.

              Comment


              • #8
                This screen shot is a quick and dirty I did in WinISD using only Qts, Vas and Fs derived with the WT3. The volume and tuning was done with default suggestions.

                Yellow is closed, no filter
                Red is closed, 1st order HPF @ 85Hz
                White is vented, tuned to 55Hz, no filter

                Is there any reason to think that this isn't an accurate representation of the low end response in each application?
                Attached Files
                Last edited by aarond; 09-12-2022, 08:40 PM.
                Thanks,
                Aaron

                Comment


                • #9
                  Those sims (w/ YOUR T/S parms) should be pretty accurate w/OUT that large series cap trying to roll off the bottom end.
                  WITH that cap, you will NOT get what WinISD shows you w/a "1st order" filter (the red plot).

                  To see what you'd end up with with the large series cap (470), you have to adjust your ISD curves by using MY plots above.
                  For the closed box, the cap does nothing @ 100Hz (so you'd keep your F3 at about 100Hz), but at 50Hz it will pull the output down an ADDITIONAL -3dB(my purple line) making it about -16dB @ 50Hz.

                  For your vented box (my green line) that cap would basically follow YOUR ISD plot to 100Hz (so, still -0dB from the ISD sim), be an additional -3dB down at 55Hz (the tuning freq., Fb), so, about -4dB, but then down only -1 additional dB @ 40Hz (giving you about -11dB @ 40).

                  Realistically, that single series cap works SOMEwhat okay on a closed box, but generates a funky "double-shouldered" rolloff in a vented box.

                  Comment


                  • #10
                    Originally posted by Chris Roemer View Post
                    Those sims (w/ YOUR T/S parms) should be pretty accurate w/OUT that large series cap trying to roll off the bottom end.
                    WITH that cap, you will NOT get what WinISD shows you w/a "1st order" filter (the red plot)...
                    That sums things up nicely, thank you again

                    Out of curiosity I might try to see what the response looks like when modeled in the small factory enclosure when I get a chance. At first it seems counterintuitive to put a woofer with these spes in such a small box but the end result is a documented solid performer. I picked these up well used at a good price. Even if they had been in good shape they still would've been pretty ugly IMO. It was an easy choice to slice them up and take a different approach and I'm still not sure what the final design will look like. I really wish the LP on the integrated sub amps was adjustable as it would make it a much easier decision to separate the subs from the main section.
                    Attached Files
                    Last edited by aarond; 09-13-2022, 04:02 PM.
                    Thanks,
                    Aaron

                    Comment

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