Re-doing Sunosub II

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  • Patrick Sun
    Super Senior Member
    • Aug 2000
    • 1380

    Re-doing Sunosub II

    Howdy folks, while I got Sunosub II up and running, I'm not quite as happy with it as I am Sunosub III, so I'm re-doing it from the bottom endcap side. For one thing, the 36" long ports are either knocking about or resonating at 40Hz at high SPL (the dts intro introduces this not so nice rattling). I'm just going to slice off the bottom endcap, and use the rest of the sonotube material for the new design (which will still net me the same internal volume as I re-port the enclosure).

    Current Sunosub II specs:

    10 ft^3 internal volume 24" wide sonotube (43.75" internal height) 3 ports 4" wide 36" long (vent mach 0.04) Tuned to 16Hz

    Future Sunosub II specs

    10 ft^3 internal volume 24" wide sonotube (41.5" internal height) 2 ports 4" wide 23" long (vent mach 0.08) Tuned to 16Hz F3 around 23Hz


    I may raise the FB tune to 17Hz (port lengths = 20") and the F3 drops to 21Hz.


    (I'm leaning towards the FB=17Hz tune, yay or nay?)


    I think I'll be okay with the vent mach at 0.08 (Sunosub III's is well over that, and I don't mind the port noise if it's present when listening at my favorite spot in the HT).

    So this means my construction web page will be delayed as I do some more MDF cutting and routing (I'll be helping Trenton route some MDF circles, so the more the merrier!)

    I'll update the revision when I get a chance.




    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
  • Stryke
    Junior Member
    • Dec 2000
    • 14

    #2
    Hi Patrick,

    As far as ports go, I generally try to keep the port length no more than 5 times the diameter. It has very little to do with the vent mach, but with regards to the compression. Typically a single large diameter port is much better than multiple smaller ports. Air is easily compressible, and trying to push a slug of air down a long narrow port usually leads to alot of compression. Multiple smaller ports will also have more internal surface area than a single larger diameter port, leading to more drag or friction. I believe this friction is known as the Reynolds number.

    A quick example would be comparing two 4" ports to a single 6" port. To achieve 17Hz tuning in your enclosure would require the two 4" ports(cross sectional area 25sq in) to be approximately 20" long. This gives a total of about 502 square inches of surface area inside the port. A single 6" diameter port will be close in length, 21.4" long, and cross sectional area(28sq in). However, the single port would only have 403 square inches of internal surface area.

    The 6" port will have slightly lower vent velocity due to the slightly larger cross sectional area, and also much less internal surface area, leading to less drag, and therefore less compression. I know there have been some tests documenting this, however I don't know where offhand. From my experiences ports 5 times longer than their diameter just don't tend to give much output. If you have the room on the endcap to fit a 6" port next to the woofer you may want to look into it.

    John

    Comment

    • Andrew Pratt
      Moderator Emeritus
      • Aug 2000
      • 16507

      #3
      interesting news pat since I have three 4" ports in my sub as well. I knew it was a comprise going into the project but so far I've not heard any knocking. I have some extra insulation stuffed around my ports to stop them fluttering around though so maybe thats whats helpping mine.




      Comment

      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        Patrick

        Things to remember. Changes of 10% in things like port tuning, box size, etc, make very little difference in the sound of a sub.

        I'm "under the weather" so that's all I can say for now, or I'll passout at the keyboard




        theAudioWorx
        Klone-Audio

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

        • Patrick Sun
          Super Senior Member
          • Aug 2000
          • 1380

          #5
          John, thanks for the info.


          Andrew, I may use some eggcrate foam to insulate the pipes and see if that helps.


          Thomas, get some rest and eat some chicken soup, pal!




          PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
          PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

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