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Dual UM-18s

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  • Dual UM-18s

    Hello all. I am looking for a little help/guidance in my build. I have 2 UM-18s in mini-martys and 2 PA-460s in MBM boxes. It is good but I want a little more. Due to WAF/room limitations I can't take up any more floor space but I don't have restrictions on building taller. Weird, huh?! So I would like to make 2 Dual UM-18s and 2 Dual PS-460s. Similar to JTR Captivators 4000ulf I want to stay ported.

    I have been working on WinISD and have a couple ideas but just want a sanity check.

    UM-18s; 18-24 cf. I get a little lost trying to determine port height (slot) and length. I think 3-5 inches tall??

    Similar situation with the PA-460s.

    Am I way off target? I could build to marty cubes and stack but unsure of WAF. Single slot port is the way I would like to go. Any advice would be very appreciated.

  • #2
    I think a 62inches^2 port heightxwidth should be more than enough (around 41-55m/s airspeed at max power, depending mostly on box size). That would be a port about 18"-wide by almost 3.5"tall (probably safe for the full 3.5inches tall to make up for the area lost to the central support) and around 16"-24"long depending on your tuning and cabinet size.

    Wait for someone else to confirm because I'm both pretty new and can't remember the proper airspeed maximum to stay under for avoiding chuffing.
    My first 2way build


    • #3
      Not sure what you're up to (what are your mains? & how low do they go?) ...

      I see 2 UM18s in a (GIGANTIC) 24cf box tuned near 16Hz (slot is 3" x 18" x 18" long). These should reach down to 15Hz (if your amp has no HP filter rolling off the bottom end). You're crossing these to the PA-460s ? ?

      A pair of those look OK in 7cf tuned to the low 40s w/a slot that's 3" x 18" x only 4" long. These should do 50Hz (where they'll hand off to the UMs?).

      They SEEM like they'd play at about the same volume if the PA pair got 100wRMS, and the UM cab got about 1200w. That volume is approx. 120dB @ 1m.

      There are MANY ways to go about this.
      (I don't know what a "mini-marty" is (size and tuning??), nor am I familiar w/an "MBM box".)
      I DO think that if you've got 4 of these running now, and it's not enough, that there MIGHT be another problem?


      • #4
        Thanks for the responses. I should have been more clear.

        Mini-marty - 12cf (24x24x40) 21" slot port tuned to 17hz.
        MBM - 4cf slot port tuned to 27hz

        Actually, I am running the 4 18s and 2 ported 15s. Love it. However, I need the floor space so I am selling the 15s.
        I also like building. And building new things. The JTR sub caught my eye, I think Mark Seaton used the UM-18s in a dual design awhile ago. So since I can't take up any more floor space, I thought let's go taller. The mini-marty almost looks a little funny with a single 18 in it anyway! Therefore, the idea of duals.

        Correct, there is a hand-off.

        I think the only 'problem' is me, my addiction. I definitely don't need this but it sounds fun.

        1. 16cf, 3.5x21.5 slot port 25 long. 20hz tune.
        2. 24cf. 5x21.5 slot port 22 long. 20 hz tune.



        • #5
          If the 24cf is for a pr of UM18s, I think that's tuned too high (ordinarily). I like the looks of 16Hz better.
          I wouldn't put a pair of the PA460s in 12cf. It SEEMs like now you've got 1 in 4cf tuned to 27Hz.
          That size seems okay (I'd put TWO in 8cf), but I think you've got that one tuned too low. I like the low 40s better. You actually gain extension on that one by tuning higher.

          I'm using Qts = 0.27, Fs = 26, and Vas = 16.7cf for the PA460-8,
          and Qts = 0.53, Fs = 20, and Vas = 7.5cf for the UM18-22.


          • #6
            Would there be a worthwhile benefit to spreading the sound-sources around more by pairing each UM18 with a PA460 (each in their own proper-sized box, but sized to stack flush one-on-another), instead of pairing UM18's and pairing PA460's and putting those pairs in seperate areas of the room?

            Or stack 2xUM18 with 1xPA460 on top (if that's possible without going too high) since it kind of looks like that'll balance your 16-50hz output and your 50+hz PA output (with the PA being so much more efficient and not needing the excursion to reach super low). ....Though it sounds like you currently have 4xUM18's and 4xPA460's, or is that what you're aiming for but don't currently have?
            My first 2way build