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Down fire an Ultimax? Assuming so, how much clearance?

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  • Down fire an Ultimax? Assuming so, how much clearance?

    I'm thinking of building a sub/end-table out of a UM18. I'll try to get it close to 4.25 ft^3, as per the kit.

    I only care about 50Hz and below.

    I've done this with other brand woofers over the years and didn't notice much difference by flipping the enclosure on it's side. Of course, that was before I had measuring equipment.

    Any thoughts on clearance and viability of the idea? I don't see a lot of down firing subs so maybe there is a larger liability than I understand.

  • #3
    Well, EYE get about 3% sag (w/lim @ 5%?).
    Pretty sure that (4cf) box is closed, w/an F3 near 30Hz (w/OUT boost).

    Keeping it @ 4.2cf and tuning it to 15Hz adds about +1dB @ 50Hz, and +2 @ 30 (and below).
    A pair of the PRs (from your other thread) fully loaded (600g ea., I THINK?) tunes 4cf near 30Hz (too high, IMO).
    A single (+600g) tunes that box closer to 20Hz (better), but the PR strokes out around 500wRMS.

    Doubling the box size (8cf), you can tune down to nearly 20Hz (2 PRs, F-L !)
    This gives a +3dB "lift" @ 30, w/an F3 at 20. Then the UM gets limited to about 300 RMS, the PRs are no where near close.

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    • #4
      Besides the initial sag, as BOBinGA addressed above, the tendency will be for the cone to continue sagging over time. That's always a bigger problem with heavy cones and soft suspensions.
      Francis

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      • #5
        Uhm- I would NOT down-fire an Ultimax, regardless the model/size. They are a very high-Mms driver, and will likely sag terribly. The 10" in my Overdrive10 sub will actually make the box shake just during normal operation to the point spikes or anchoring are required. Sub-par performance will occur if down-fired.

        Later,
        Wolf
        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
        "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
        "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
        "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

        *InDIYana event website*

        Photobucket pages:
        http://photobucket.com/Wolf-Speakers_and_more

        My blog/writeups/thoughts here at PE:
        http://techtalk.parts-express.com/blog.php?u=4102

        Comment


        • #6
          I really appreciate the help.

          Woofer orientation is a bit of an issue for us. Maybe I will have the woofer face the wall.

          I could build a grill but the flange and surround are over an inch thick and the xmax is about another inch. It's going to look like a giant, cloth covered, box stuck to the side of another box. lol!

          I picked up some cloth but I suspect this end table is going to end up with no grill.

          Comment


          • #7
            If the mms is that high I'd be more worried about cone sag mounting vertically. If the cone sags the voice coil will rub on the pole piece and bye bye.
            Horizontal mounting will keep the voice coil centered in the gap if it sags.
            Cloth/ accordion pleat surrounds do not sag. I built a pair of down firing 18 inch subs over 20 years ago. No cone sag period. In box qts .36.
            I used Eminence LF drivers with a 4 inch voice coil and large magnets.

            To get the balls of the Ultimax you would need at least 12 cubic feet due to its high qts (.53). That will give an f3 of 17 hz. with
            about a 3db ripple response (BB4 alignment). Better transient response than the other alignments.
            Too bad they only have a 3 inch voice coil. For that cash outlay I would expect more.

            I've only ever experienced cone sag once. Fender Princeton stereo chorus left too close to an open window at night. The cones got slightly damp from the humidity and both cones eventually sagged and rubbed. Luckily it was still in warranty.
            Has anybody ever experienced real cone sag from horizontal mounting or is it just an old wives tail ?

            Comment


            • #8
              Cone sag is no joke.
              Wolf
              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
              "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
              "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
              "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

              *InDIYana event website*

              Photobucket pages:
              http://photobucket.com/Wolf-Speakers_and_more

              My blog/writeups/thoughts here at PE:
              http://techtalk.parts-express.com/blog.php?u=4102

              Comment


              • #9
                You can always rotate 'em (every 6Kmi).

                Comment


                • #10
                  Originally posted by Regore View Post
                  If the mms is that high I'd be more worried about cone sag mounting vertically. If the cone sags the voice coil will rub on the pole piece and bye bye.
                  Horizontal mounting will keep the voice coil centered in the gap if it sags.
                  Cloth/ accordion pleat surrounds do not sag. I built a pair of down firing 18 inch subs over 20 years ago. No cone sag period. In box qts .36.
                  I used Eminence LF drivers with a 4 inch voice coil and large magnets.

                  To get the balls of the Ultimax you would need at least 12 cubic feet due to its high qts (.53). That will give an f3 of 17 hz. with
                  about a 3db ripple response (BB4 alignment). Better transient response than the other alignments.
                  Too bad they only have a 3 inch voice coil. For that cash outlay I would expect more.

                  I've only ever experienced cone sag once. Fender Princeton stereo chorus left too close to an open window at night. The cones got slightly damp from the humidity and both cones eventually sagged and rubbed. Luckily it was still in warranty.
                  Has anybody ever experienced real cone sag from horizontal mounting or is it just an old wives tail ?
                  A larger voice coil is appropriate for Pro Audio use where the driver is expected to be used for more than low bass, but otherwise 3 inch is plenty with the latest high-temperature glues and voice coil formers, especially for a sub. Typically you'll exceed Xmax long before you pump too much heat into the coil.
                  Francis

                  Comment


                  • #11
                    I wanted to stay away from foam or rubber surrounds which is why I chose a pro audio driver. I've used 3 inch voice coils on 15 inch subs and they worked well but for 18s 4 inch coils were the only way to go to get the specs and BL (horsepower) I required. Adjustable legs were set at 2.5-3 inch clearance from the floor. I also used Burke tubes for the 18s and sonotubes for the 15s. The Burke tubes are much thicker and stronger than the sonotubes. The 18" bass tube vol.=13 cubic feet. They are 24 inch diameter about 5 feet tall plus legs. Top loaded port 8 inch diameter and 18 inches long yielded a FB of 20 hz and an F3 of 18 hertz. with no assist and zero port noise at 18 hz.. Once you get down to the low 20s and high teens with high SPLs it is possible to cause damage to your home or contents. Both 18s were also mass loaded about an extra 80% of cone mass to bring the QTS and FS to the Thiel/ Small specs required. Pro audio drivers often have too low a qts and too high a fs for 20 hz reproduction at high spls The mass loading took care of both issues. The qts was raised from .28 to .34 and the fs was lowered from 24 to 20 hz. VAS dropped from 22 to 18 cubic feet. Down side is you lose some power handling. Electronic crossover set at 42 hz. 24 db/ octave low pass.
                    QL losses are also much improved using tubes. One measured 10 and the other was12. These are very good numbers for 18 inch drivers with lossy surrounds.
                    Measured in box qts was .36 which was my design goal. They also work very well in large rooms (4000 cu.ft or more).

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