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Optimal Weight on Passive Radiator Subwoofer Build

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  • Optimal Weight on Passive Radiator Subwoofer Build


    I am just finishing up a Subwoofer build with a passive radiator. I am new subwoofer design and passive radiators.

    I am using a Dayton Titanic MK4 10" for the driver and a Dayton 10" Aluminium cone passive radiator. The enclosure is net 1.54 cu. ft. the walls are sealed with caulking and lined with cotton insulation about 1" thick.

    I used WinISD and Unibox Pro to simulate the build. The optimal value on WiniSD seems to come up at 4 disks (225g additional) and Unibox Pro seems to be 3 disks(150g additional). If anyone has Bassbox Pro I would be curious to see what they get. Is the final tuning best done with REW?

    Any help greatly appreciated.


  • #2
    For ME, WinISD (Pro) shows best rolloff in 1.5cf w/NO added mass (F3 in the low 20s.) I'm using Qts = 0.39, Vas = 1.08cf, and Fs = 29.6Hz.

    Also, it shows your (single) PR running out of Xmax at about 220w RMS.
    MOST would say that for any sub, the PR (or multiples) should be capable of twice the swept volume of the active driver. (In short, for a 10" driver w/18mm of stroke, you should use a 12" PR (w/similar stroke), or a pair of 10" PRs (w/same stroke), OR a single 10" with double the Xmax, so... 36mm. Your single 10" MIGHT not be up to the task.


    • #3
      Thanks for the reply, I will double check the numbers on the driver in WinISD With no added mass I get f3 at 30 Hz. The titanic driver model I am using has a Qts=0.402(calculated), Vas = 1.077(entered) and Fs = 29.6 Jz(entered), same as yours. Even turning off the HPF my F3 is still 30 Hz. Any ideas on where I am going wrong?

      I am planning on using a SPA250DSP amp(arriving this week) and turning on the LPF(25 Hz and N=2). I went with one 10" PR after simulation since the Titanic MK4 driven with 250W power and HPF filtering would keep me below Xmax on both the PR and Driver.

      Maybe I have the wrong version of WinISD, says no PRO

      Edit: Got the same results I previously had with WinISD not pro and edit Typo on Qts
      Last edited by helicon; 02-25-2018, 06:23 PM.


      • #4
        Originally posted by helicon View Post
        The titanic driver model I am using has a Qts=4.02(calculated),
        I don't think so!
        Don't worry, if your parachute fails, you have the rest of your life to fix it.

        If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

        Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D


        • #5
          Thanks for catching the typo. When I said Calculated, I did not mean by me, but by WinISD. With the information corrected do you have any guidance to give?


          • #6
            My WinISD states: "0.50a7". It's pretty old. I've never seen a WinISD that spit out wrong info. There might be a 1-2% variation between different vers., but nothing that would really matter in the real world.

            THAT 10" PR uses 75g weight disks. So, 2 = 150g, and 3 = 225g. (That doesn't really jive w/your earlier post.) Anyway, that Mk4 10" (our Qts variation would only change freq. by maybe 1Hz, and box vol. by maybe 5%, insignificant in my mind) comes up w/NO added mass as though you'd actually like to REMOVE mass from the PR (the tuning looks too low). Adding any mass drops the tuning, raising the F3.


            • #7
              You are correct. I simmed 3=225g and 4=300g. Should have paid better attention. Wonder why we are so far off. If I do no added mass it looks terrible and dives hard before 30 Hzish.


              • #8
                Click image for larger version

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                I've duplicated your Qts, Vas, and Fs values.
                Check the values of your PR (esp. the "units" - like for Sd).
                Green curve is YOUR 1.54cf box w/NO added mass.
                White curve is just ONE 75g mass added, and already the F3 has risen almost 10Hz. The NO added mass curve is much better.
                PRs DO drop off a bit more steeply than ports do.
                30Hz is way more than you need for (almost) ANY music, and it's pretty dang good for movies as well (20Hz not so necessary).

                You CAN get a bit better F3 by going w/TWO of those expensive 10" PRs, but I'd definitely try this box w/one PR w/out extra mass. Looks good to me.


                • #9
                  Click image for larger version

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                  Great thanks for providing the graph. Looks like we are getting the same results. The red trace is with no added weight and the blue trace is with 3 disks added, 225g. I guess my thoughts were with the DSP amp I would enable the high pass filter(fc=25Hz, n=2) and add a PEQ (fc=27Hz, Q=1, Gain = +4dB) to create a peaking high pass filter, the black trace. Since both filters are digital, the net gain would be about +2dB, so the max excursion of driver and PR would be below Xmax. Is the initial characteristic of the blue trace bad, with the sort of change in deccay rate?

                  Thanks again for your help.
                  Note: I have simulate voice coil inductance off hence the lack of hump and roll off at the high end
                  Last edited by helicon; 02-26-2018, 11:34 PM. Reason: Removed extra images, added comment about voice coil inductance