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6" Ports for Ultramax 18?

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  • 6" Ports for Ultramax 18?


    Just purchased two of the Dayton Audio UM18-22 Ultramax subs on Memorial Day. I am going to build DIY boxes appx 8 cubic feet each as recommended for home theater. My question is that they recommend 3 4” flared ports at 29” each. PE doesn't sell anything even close 29" ports so I'm a little confused. What would the length be if I was to use one or two 6” flared port(s) instead?

  • #2
    If you end up with the same flow area, you need the same length of port. There are couplers to join lengths of port together (see below), then you add flares to the ends. Alternately you can use PVC pipe. The flares on the ends is the only tricky part, but that's doable, although I haven't done it. You may also have to use plumbing elbows to get the port inside the box.

    https://www.parts-express.com/dayton...-ring--268-336
    Francis

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    • #3
      This situation BTW is one where it is appropriate to use a passive radiator.
      Francis

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      • #4
        1 - 6"id x 19" long (1st resonance at 360Hz).
        2 - 6" x 42" long (1st resonance at 160Hz ).
        These are tuned to and have an F3 near 20Hz.

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        • #5
          You need quite a bit of passive radiator to keep up with the surface area and excursion of a UM18.

          Since you're building your own cab, consider a slot port. In the common 'MartySub' design and zillion variants, the slot port is full width minus some bracing, height and length tweaked for tuning and port velocity. Full width slots are really easy to build. Make sure to subtract the volume of the slot, slot walls, and all the bracing your 8ft high powered sub needs, from your internal volume.

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          • #6
            Originally posted by Prana Ferox View Post
            You need quite a bit of passive radiator to keep up with the surface area and excursion of a UM18.

            Since you're building your own cab, consider a slot port. In the common 'MartySub' design and zillion variants, the slot port is full width minus some bracing, height and length tweaked for tuning and port velocity. Full width slots are really easy to build. Make sure to subtract the volume of the slot, slot walls, and all the bracing your 8ft high powered sub needs, from your internal volume.
            Yeah, that's a good alternative. As long as the slot aspect ratio doesn't get too high, and you flare the entrance and exit, that should work well.
            Francis

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            • #7
              Originally posted by blownsi View Post
              Just purchased two of the Dayton Audio UM18-22 Ultramax subs on Memorial Day. I am going to build DIY boxes appx 8 cubic feet each as recommended for home theater. My question is that they recommend 3 4” flared ports at 29” each. PE doesn't sell anything even close 29" ports so I'm a little confused. What would the length be if I was to use one or two 6” flared port(s) instead?
              You can buy three 4" Precision Ports and then order their 4" tubes with no flares and the 4" connectors to get the length you need to be at.

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              • #8
                Thanks everyone.

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                • #9
                  Just curious, if three 4" ports are suggested, and I think that roughly equals two 5" ports at the same length, what made you lean toward two 6" instead? Availability, chuffing worries, something else?
                  My first 2way build

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                  • #10
                    Making & bracing 29" long ports seemed insane so I was hoping to run twin 12" or so length larger ports. In reality both are difficult to deal with and a slot port is more ideal. I just can't wrap my head around designing a slot port. I get that it's sort of like a small box around the outside of another box but I just can't visualize it let alone calculate it. I'm still searching through various threads hoping to come across something I can DIY. I was gonna built those flat pack mini martys until I figured out that shipping is more expensive than the actual wood. I may end up having to go with sealed boxes.

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                    • #11
                      For your 8cf box, a slot that was 2" tall and 20" wide, by 30" long would work (Fb and F3 near 20Hz).
                      Here's what it'd look like (diff. scale and aspects though - this is a 10" in less than 1cf).

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                      • #12
                        Originally posted by blownsi View Post
                        Making & bracing 29" long ports seemed insane so I was hoping to run twin 12" or so length larger ports. In reality both are difficult to deal with and a slot port is more ideal. I just can't wrap my head around designing a slot port. I get that it's sort of like a small box around the outside of another box but I just can't visualize it let alone calculate it. I'm still searching through various threads hoping to come across something I can DIY. I was gonna built those flat pack mini martys until I figured out that shipping is more expensive than the actual wood. I may end up having to go with sealed boxes.
                        Try thinking about it as a big box sitting on a small box with a common side and a hole in it. Figure out the size of ports you need then adjust the size of the the speakers enclosure. If you use something like BassBox it's a vented enclosure with an external port. Here's a couple pics that might help

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                        • #13
                          IF you're aiming for shorter port length at a similar tuning, you'll need either fewer ports of the same-ish or smaller diameter or simply smaller diameter ports. This will, however, increase the likelyhood of port noise/chuffing, particularly at higher volumes.

                          Changing from three 4" ports to a single port will lead to a single port with internal diameter around 7.25"....at the same 29" length. Changing that to a slot port is mostly just squashing the shape down to a rectangle like the 2"tall X 20"wide by 29"-30"long that ChrisRoamer mentioned earlier. Inside a large 8cu-ft box you can probably fit the port along the bottom and partway up the back by only around 8inches or less depending on the depth of your box.

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                          If the box can lay on its side (so it's short and wide) you might instead be able to fit a slightly shorter and slightly smaller diameter PVC pipe/port in the long/tall way...something like 6.5" internal diameter by 24" long. Or a pair of 4.5" by 24"long ports. Or simply use a PVC elbow to help fit a full length, full diameter port like fpitas already mentioned.
                          The full-size port like fpitas mentioned or the fullsize slotport like ChrisRoamer mentioned should both perform better than a smaller+shorter port configuration.
                          My first 2way build

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                          • #14
                            https://www.parts-express.com/dayton...iator--295-506 Try two of these in each box. problem solved.

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                            • #15
                              Originally posted by analogkid442 View Post
                              https://www.parts-express.com/dayton...iator--295-506 Try two of these in each box. problem solved.
                              That is the normal way to deal with this, but it's also $300.
                              Francis

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