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Suggestions on first build - UM10-22 ported subwoofer, 1.7 cuft, 20Hz f3

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  • Suggestions on first build - UM10-22 ported subwoofer, 1.7 cuft, 20Hz f3

    Hi guys! After months of planning and countless options scraped, i think i finally found a good direction for my project of a subwoofer to add to my 3.0 home theater system (70% movies / 30% music).

    Aims:

    * make use of a SVS PB-1000 amplifier board i got for free
    * try to reach a f3 of 20Hz, without necessarily getting to super high volumes (i live in a apartment after all)
    * try to keep sizes as small as possibile
    * try to keep costs from skyrocketing


    Using WinISD i got what looks like a satisfying configuration for a Dayton Ultimax UM10-22 in a 1.7 cubic feet internal volume box, tuned to 22.5Hz:

    * with a 102.66cm long, 3x30cm vent (or 40.4" long, 1.18x11.8") it reaches a f3 of 19.5Hz
    * it can be fed 130W before exceeding its max cone excursion
    * at 130W, SPL in the flat region of the graph is between 102 and 103 dB (almost 99dB at f3)
    * at 130W, maximum air velocity is around 16 m/s

    Here's the graphs: https://imgur.com/a/cM8CMtz

    Now, the port is pretty long, so the only way to fit it in a box is to fold it.
    With the same internal voulume and port length, i got 2 different enclosures:

    * first one (1-folded vent) is 33.8(W) x 52.5(D) x 49.8(H) cm (or 13.3(W) x 20.6(D) x 19.6(H) inches)
    * second one (2-folded vent) is 33.8(W) x 36.6(D) x 73.5(H) cm (or 13.3(W) x 14.4(D) x 28.9(H) inches)

    Having a much smaller footprint, maybe i'd rather go for the second option.

    Here's the pics:

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    Given that this would be my first build, i'd like to receive some feedback / criticism!

    * Is there any obvious flaw in my project?
    * Is that 16 m/s max air velocity acceptable? Will i get noise from the port?
    * Group delay peaks at around 41 ms: is that too much? I got the feeling that folded designs can't hope to get much better than this
    * Is a folded vent a problem or is it an acceptable solution? Any downsides to it?
    * Are there rules on the best placement for the driver? Close to the top / bottom or centered? In the second design i placed the driver close to the ground to keep the center of mass as low as possible. This placement puts it far from the vent though, and i'm not sure if that's a good thing, a bad thing or if it doesn't matter at all
    * bracing: how much is enough? Will something like 6 3" wide pieces (3 on each side) be enough?




    Thanks in advance!
    Attached Files

  • #2
    Nothing wrong with folding a port, but the aspect ratio of your slot port seems pretty high. When you make a port so small in one dimension you'll get air flow losses. But, I'm no slot port expert. Maybe one of them will weigh in with a rule of thumb etc.
    Francis

    Comment


    • #3
      Funny, I made this pair up about 5 yrs ago.
      DATS ave. for a pair of 2.

      Qes 0.71, Qms 3.9, (Qts 0.60)
      Fs 31, Vas 0.68cf
      Re 3.2, Le 1.2mH
      (used dia of 8.0" = Sd of 325cm^2)
      Xmax 19mm, Pe 500w

      Comment


      • #4
        Originally posted by fpitas View Post
        Nothing wrong with folding a port, but the aspect ratio of your slot port seems pretty high. When you make a port so small in one dimension you'll get air flow losses. But, I'm no slot port expert. Maybe one of them will weigh in with a rule of thumb etc.
        I went for a port that takes all the cabinet's length because it's both the simplest design to build and the one with less impact on the internal volume, as you don't need to add vertical walls. Ratio here is 1:10, and now that you make me think of it, on both Carmody's Pony sub and MartySub ratio is 1:7.5. I see a pattern here.
        Here they talk about a maximum 1:8 ratio, but others don't seem to agree... Waiting for the experts, i guess.


        Originally posted by Chris Roemer View Post
        Funny, I made this pair up about 5 yrs ago.
        DATS ave. for a pair of 2.

        Qes 0.71, Qms 3.9, (Qts 0.60)
        Fs 31, Vas 0.68cf
        Re 3.2, Le 1.2mH
        (used dia of 8.0" = Sd of 325cm^2)
        Xmax 19mm, Pe 500w
        Ah! At first i thought it was a crazy coincidence, but then again if you want to get an acceptable port length and air velocity, while keeping the box volume and f3 low, it looks like there aren't so many options...
        Did you build those? How do they perform? Any port noise?

        Comment


        • #5
          I built this one:

          Click image for larger version  Name:	 Views:	0 Size:	85.0 KB ID:	1440743
          Built using 3/4" stuff, outside dims: 12"w, 17-3/8"h, 18-3/8"d (or long). Slot is 1"h x 10-1/2"w by 52" long.

          No chuffing (although it's BEST to aim the slot away from your listening position - just in case) with a generous "roundover" on the exit (w/a router bit).
          Modeled in WinISD. Aim Fb was 24Hz. DATS verified Fb within +/-1Hz. Now, I wouldn't want to make the width (slot "height" - here) any less, 'cause think about it this way:

          If you need 20 sq.in. of slot area (for proper flow), and you consider that "drag" occurs around the slot's perimeter:
          A 4" x 5" slot will have 18 (lineal) inches of perimeter, whereas a 2x10 will have 24, a 1x20 would have 42, and a 1/2"x40" ends up w/81".
          I THINK that's where the "ratio rule" comes from, but it depends on many other things (w/velocity being a large factor).
          Low power woofers (and those w/limited Xmax &/or Sd) won't push enough air fast enough to have enough drag for the tuning to seem altered. Drag rises exponentially with velocity. I've heard a pair of Overnight Sensations that had pretty narrow slots (1/2" x ?) that sounded great at normal playback levels. It all depends.

          I do recommend using spacers between your slot "fins" (while gluing them in place). You can see in a model that having the narrow slot dim off by just a little (< 1/8") CAN throw your tuning off by a lot.
          The narrower the slot, the worse it can become. Having the length off by several inches (on a long vent) won't hardly change the bottom end at all.
          Last edited by Chris Roemer; 05-17-2020, 01:36 PM.

          Comment


          • #6
            I'm going to add that the UM series is really not best in vented cabs. The designer himself optimized them for sealed applications with maybe boost applied.

            To the OP- If you want smaller than you have there, my Overdrive10 project fits the niche. It's a 26 ltr PR-terminated bandpass, and it is GREAT for home theater!

            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


            • #7
              The most efficient vent is a port tube as a circle maximises the ratio of area to perimeter. As Chris talks about above, as the vent gets farther from square the ratio of area to perimeter keeps decreasing and that decreases your effective flow area. The formula for this is Dh = 4A / P where Dh is the equivalent diameter of a round port based on the division of 4x the area by the total perimeter.

              I have always tried to keep to a height/width ratio no more than 1:6 but that doesn't always work out based on aesthetics. I recently built a slot that was 1/4" x 4.5" which is 1:18 but I adjusted the length accordingly. It was a test box at low power and worked fine. I did use a 1/2" roundover at the exit and rounded over all internal corners of the vent.

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              Comment


              • #8
                It's a matter of degree. Even a port with a huge aspect ratio, like 1:100, will work at very low power, with low port velocity. Once you're talking subwoofer though, you expect to move serious amounts of air.
                Francis

                Comment


                • #9
                  Chris Roemer , Dukk , fpitas : i can see the problem with the vent, thanks.
                  I think that can be easily worked around with something like this:
                  Click image for larger version

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                  Vent area and internal volume are the same as before (and so is vent length), but i adjusted the port ratio: now it's 9cm (H) x 9cm (W), or 3.54"(H) x 3.94"(W). What do you think?

                  Wolf : why do you say it's not the best in vented cabs? I've tried to model a whole bunch of other Dayton drivers (probably all the 8" and 10" available), but nothing seems to give such a flat and low response as the UMs, in a small enclosure at least. Am i missing something?
                  As for the Overdrive, i obviously took it into consideration as it's one of the few projects i could find with a smallish driver, a small size and a low extension (at first the choice was between the Overdrive and the digger8 :D). The thing is it's quite a bit pricier and seems like it's reliant on that specific amp, while i'd like to make use of the one i already own to make the final thing even cheaper.
                  Attached Files

                  Comment


                  • #10
                    Originally posted by SavageButcher View Post
                    Chris Roemer , Dukk , fpitas : i can see the problem with the vent, thanks.
                    I think that can be easily worked around with something like this:
                    Click image for larger version

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Size:	274.5 KB
ID:	1440834


                    Vent area and internal volume are the same as before (and so is vent length), but i adjusted the port ratio: now it's 9cm (H) x 9cm (W), or 3.54"(H) x 3.94"(W). What do you think?

                    Wolf : why do you say it's not the best in vented cabs? I've tried to model a whole bunch of other Dayton drivers (probably all the 8" and 10" available), but nothing seems to give such a flat and low response as the UMs, in a small enclosure at least. Am i missing something?
                    As for the Overdrive, i obviously took it into consideration as it's one of the few projects i could find with a smallish driver, a small size and a low extension (at first the choice was between the Overdrive and the digger8 :D). The thing is it's quite a bit pricier and seems like it's reliant on that specific amp, while i'd like to make use of the one i already own to make the final thing even cheaper.
                    If your port velocity is reasonable, that port should work much better. You may want to consider a flare at the inlet and outlet, once again for minimum air flow losses.
                    Francis

                    Comment


                    • #11
                      Originally posted by fpitas View Post

                      If your port velocity is reasonable, that port should work much better. You may want to consider a flare at the inlet and outlet, once again for minimum air flow losses.
                      Port velocity didn't change from the initial data, it still peaks at 16m/s (before reaching cone excursion).

                      I will make a flare at the two ends for sure: does making it change the effective port lenght?

                      Comment


                      • #12
                        Originally posted by SavageButcher View Post

                        Port velocity didn't change from the initial data, it still peaks at 16m/s (before reaching cone excursion).

                        I will make a flare at the two ends for sure: does making it change the effective port lenght?
                        The rule of thumb is the port length is taken as halfway through the flare. That actually depends on the particular flare, but it gets you within shouting distance.
                        Francis

                        Comment


                        • #13
                          I don't know if you're set on a port, but a PR works well in my opinion. I rear mounted the UM10 with a RSS315 12" PR and it works great!
                          Attached Files

                          Comment


                          • #14
                            Model well in ported/vented- I suppose it does. It was not the intention of the driver designer.
                            I didn't design them, but taking the word of the engineer has its merits.
                            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


                            • #15
                              Originally posted by Wolf View Post
                              Model well in ported/vented- I suppose it does. It was not the intention of the driver designer.
                              I didn't design them, but taking the word of the engineer has its merits.
                              Later,
                              Wolf
                              What kind of problems might someone run into with a subwoofer in a ported enclosure with modelling showing a decently flat frequency response down to the port, and the port size/length optomized to avoid chuffing while the woofer will stay under Xmax?
                              I don't mean this in a snarky or challange-y way, and it doesn't have to specifically be about the UM10", I'm honestly curious what kind of problems a subwoofer can run into with a ported box when FR/extension, port-noise and Xmax are kept in good shape. Are there some other problems to look out for, or is it a situation where SIMs/models tend to get things wrong?
                              My first 2way build

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