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Buyout isobarik 8" subwoofer. Port questions and design reveiw.

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  • Buyout isobarik 8" subwoofer. Port questions and design reveiw.

    I am mounting 2 http://www.parts-express.com/930064-...4-ohm--299-363 in a .5cf box with ether 1 2inch port or 2 1.5 ports the woofers will be facing face to face.
    Is there any reason to choose 1 port over 2?

    With the woofers face to face will the cardboard gasket be enough to seal things or should I use some sealing foam?

    If I were to change the configuration to one woofer firing up and one woofer firing down in reverse polarity would that still function the same as face to face? It would seem to be a better way to do it sense I would have twice the cone surface.

    Thanks for the help with this cheap/fun subwoofer.

  • #2
    Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

    Originally posted by kenrhodes View Post
    I am mounting 2 http://www.parts-express.com/930064-...4-ohm--299-363 in a .5cf box with ether 1 2inch port or 2 1.5 ports the woofers will be facing face to face.
    Is there any reason to choose 1 port over 2?
    The only reason to do a pair of 1.5" vs. a single 2" would be increased port area to reduce chuffing. You will be limited to about 80W power handling total, which should be fine with the single 2" dia. port (12.5" length would tune to 35 Hz in .5 cf).

    With the woofers face to face will the cardboard gasket be enough to seal things or should I use some sealing foam?
    I would be concerned about air leaking through the gaps in the segmented gasket. Some additional sealant once mounted face-to-face would be a good idea.

    If I were to change the configuration to one woofer firing up and one woofer firing down in reverse polarity would that still function the same as face to face? It would seem to be a better way to do it sense I would have twice the cone surface.
    I'm not quite following you here. It sounds like this would not be an isobarik setup, but standard "push-pull", so you would need a larger enclosure for this option -- correct? That would be the only way you would end up with twice the cone area.
    | there is no spoon... |

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    • #3
      Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

      Thanks for the help. I have the baffle almost done, I have the rest of the box cut and almost ready for assembly. I hope to be testing tonight or tomorrow.I think it will be a fun build and I can compare it to a friend that has the same woofer with in a 2 cubic ported box.
      After reading a few articles about magnet to magnet isobaric loading they all suffer from the large air space between them acting like a spring. Clamshell seems to be the best way to load the woofers, cone to magnet the second best way to lead them.

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      • #4
        Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

        Looks like a lot of fun!

        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
        My Voxel min sub Yet-another-Voxel-build

        Tangband W6-sub

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        • #5
          Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

          The box is glued up and should be dry in the morning. I will have to cut and install the ports, mount it on legs, install the amp and subs then test and tune. total size should be 12x12x16 not too bad.

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          • #6
            Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

            Sorry if this information is obvious to you... I'm just throwing it out there.

            Those are 4 ohm woofers, so unless you can deal with a 2 Ohm load, you're going to want to wire them in series, right? Make sure to reverse polarity on one of them.

            I've done several isobaric subs through the years and found the front-to-front configuration the easiest to build. It eliminates the need to build a chamber between the two cones. Definitely use some weather stripping as a gasket between them.

            Oh yeah... in this close-coupled, isobaric configuration the Vas decreases by a factor of two, so your box volume should be half the size as a single woofer would normally need. This makes for nice, small subwoofers in cars that would otherwise be twice the size. The only disadvantage is having to buy two woofers. (tradeoff between small size vs. increased cost .)

            Funny story... I helped a college buddy build a twin 12" isobaric subwoofer (four 12's) for his car about 15 years ago. Somebody broke into his car and stole the front two woofers but couldn't steal the two inner drivers as they were mounted from the inside of the box.

            Best of luck to you. Keep us updated.
            ~Marty

            Baby Eidolons
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            • #7
              Re: Buyout isobarik 8" subwoofer. Port questions and design reveiw.

              I got everything cut but nothing installed yet. I hope to be able to burn some of the midnight oil and get things working tonight so I can test throughout the week.

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