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Ultimax 8” truck sub

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  • Ultimax 8” truck sub

    Hey guys, I’m putting together a truck system and bought the ultimax 8” for a sub. It’s been quite a while since my last one, I was hoping someone might be willing to run some numbers? I’m hoping that a slot ported box tuned to as close to 30hz as possible is practical. I have 11”x11”x17” in my console to work with. I don’t need it loud, but I’d like to dig as deep as possible. I’ll be using a Ken wood amp rated at 300wrms@4ohms. I never want to listen at more than 90db and usually much less.

  • #2


    • #3
      11x11x17 minus 1/2" wall thickness and basket ~.7ft.³ or 20l. The port noise should be irrelevant since you plan on using a slot. Did not model it with more or less volume.

      Click image for larger version  Name:	ulta8 sealed.JPG Views:	1 Size:	156.4 KB ID:	1423431 Click image for larger version  Name:	ulta8vent.JPG Views:	1 Size:	163.1 KB ID:	1423432 Click image for larger version  Name:	ultaxmax.JPG Views:	1 Size:	97.2 KB ID:	1423433

      Click image for larger version  Name:	ultaport.JPG Views:	1 Size:	89.7 KB ID:	1423434


      • #4
        Thank you very much!! So if I am converting the round port correctly my slot will be about 1”x10”x17”?


        • #5

          I get 0.8 cu.ft. using 3/4" walls (9.5 x 9.5 x 15.5)
          Anyway, to tune a 0.8 (or 0.7) cf box to 30Hz you'd need a 1x10" slot that was 37" long!
          That slot w/a 17" length tunes into the low 40s.

          In any case, given a high-pass of 60Hz gives you a (-3dB) bandwith that's very "one-notey" from 40-65Hz.
          Most here would probably recommend a closed box. THAT would yield a bandwidth from lower 30s to 80Hz (nearly twice as wide, and actually going deeper).
          Neither of those even consider "cabin gain" (maybe +12dB / octave?).


          • #6
            What Chris said. Sealed is the first sim and that's probably the way I'd go.

            Chris, with liberal amounts of eq. would you still choose sealed?



            • #7
              In the sealed sim I see qtc at .5, .707 is the goal right? So does that mean I would benefit going just a bit larger on the enclosure? Or am I looking at the wrong numbers? Sorry for all the questions. I also thought going ported would make it easier to eq and get more output down low?


              • #8
                In 0.8cf I see a Q(tc) of about 0.80. Smaller box would raise that.
                0.80 is pretty flat (.70 target). My Large ADVE\TS were even higher, like 0.90 (or higher).
                Fully stuffing the box (polyfill or fiberglass) will effectively lower the Q a bit.
                If you +12dB (for cabin gain - Google it), you're almost flat below 25Hz.
                Most music won't go below 40Hz.
                What's your thinking?


                • #9
                  I wanted output down into the 30s, and definitely not a one note boom boom. I’ll happily go sealed. I haven’t put a sub together for years and apparently I’ve forgotten a lot. The laptop I had the modeling software is long gone☹️. I really appreciate you guys helping out. My other subs were home theater, big giant ported things that my wife barely puts up with lol. I haven’t seen too many sub builds using the center console to hide the driver. I’ll get some more pics up, hopefully it will help the next guy out...


                  • #10
                    mrmky The first figure is for the sealed box; Qtc. is in the Qtc box @ .89 and that was modeled with heavy fill. Been a while since dabbing in car audio but I don't think it will be too boomy in this application. You could port the box, say you use 4" pvc as a port, and IIRC, there is a pvc endcap that will fit inside the 4" creating an effective plug. Rummage through your local hardware store's plumbing section till you find something that works. That way you can have it both ways. Don't like it ported, plug the hole.

                    Sealed will be an easier build. YMMV, but I like the denim insulation better than polyfill.

                    Most car guys around here want loud and couldn't be worried less about quality. As far as that goes, so do most home audio peeps. WalMart sells the good stuff. Nice to hear someone NOT wanting boom!

                    Have no idea how far head units have come in the past couple decades, but something like a minidsp gives the user a lot of control over their system. That would be a must-have if I were to do another car build.

                    Chris, did you subtract port and basket displacement from the box volume? Curious as to why we are so far apart on volume and you using 3/4" to my 1/2". Personally, I get confused easily and find it best to leave the figuring to a volume calculator like this

                    Last but not least, how are you guys getting around how embedded the infotainment system is with the vehicle's overall electronics system?


                    • #11
                      This is a 2002 f-150 crewcab. It’s a work truck so nothing fancy. Audio controls are not on the steering wheel. I just wanted something nice to listen to, aftermarket door speakers front and rear, new head unit, 4 channel amp, and a modest sub to fill in the bottom.

                      i actually do have a minidsp 2x4 just sitting around and a umic as well, can it make that much of a difference for car audio?


                      • #12
                        Back in my car audio days I would have sold body parts to have something like the minidsp.


                        • #13
                          Since this is a car application I would go with a sealed box with an F3 between 55-50hz, the cabin gain will fill in the bottom end and give a smooth response.