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bends in port tube

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  • bends in port tube

    Never had to deal with this, but for a BP using my drivers, I need a very long port. ( 4 inch) I have seen the suggestion you measure centerline for length. Is there any factor for losses/friction for each bend? I will prototype and tune of course, just looking for first pass guidance. I assume the large radius bends are preferable to the tight ones. ( Dust collector pipes have largest radius) PRs are not appropriate for this build.

  • #2
    I haven't seen bends cause a deviation from what was modeled.
    I made a bandpass once with nothing but 3" elbows from the big box hardware store, used the centerline for length and it modeled pretty much as expected. Can't remember specifics, but it was close enough to be close enough if you know what I mean. That was for a car trunk. The radius was probably 3 inches on that one if I remember.

    PE sold a port kit awhile back with really sharp bends, almost no radius at all on the inside corner, I always 'thought' it was too sharp, but I suspect it was probably okay with only one bend in it for a speaker system. Yeah, I'm no help.

    TomZ
    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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    • #3
      Cool.

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      • #4
        Looked at the price of 4 inch 90's. Think I will cut 45's and glue it all up. I wonder, has anyone tried the semi rigid aluminum expanding dryer duct? Glue it to a wall so it can't flop or vibrate.

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        • #5
          Once I get 4 inch and larger I like to build my own square ports out of plywood. Cardboard tubes work well where you can miter and glue elbows. I've mitered and glued pvc pipe up to 3 inches. Might be good to use multiple smaller ports. Ductwork would be way down on my list unless I could make it non resonate with some sort of wrap.

          Added; plywood port doesn't need to be square. I've made slot ports that work great.
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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          • #6
            Should be able to find different radius and different length bends at the local hardware store. They have several 'grades' of pvc from high pressure (schd 80 and above) to sewer and drain, to conduit. A 3" 90* S&D elbow is generally less than $2 locally. Since pulling wire is a concern through conduit, it can have a rather large radius but the price is considerably higher. One thing with pvc vs mitering/gluing your own is the smooth inner surface of the manufactured elbow.
            http://techtalk.parts-express.com/fo...khanspires-but
            http://techtalk.parts-express.com/fo...pico-neo-build
            http://techtalk.parts-express.com/fo...ensation-build

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            • #7
              Big price jump for 4 inch. Huge additional difference for the large radius. I have also thought about a slot vent. For a sub, I wonder how "resonate: a bit of expanding duct actually is. I think I will test it.

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              • #8
                JL Audio marketed a plastic version of the flexible vent for its car audio enclosures in the 90s. They didn't offer it for long - most likely due to cost than anything. I always thought the rough interior of it (corrugated) would play hell with turbulence and resultant noise.

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                • #9
                  It's a vibrating air mass, not a high performance internal combustion engine intake runner. Slot ports routinely have right angle bends.

                  Edit: Foam core fiberglass layup, make anything you want.

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                  • #10
                    Foam panels make excellent resonators, it would be interesting to see if wrapping with fiberglass stiffens/ helps. Lots of you tube videos on poor mans fiberglass that could also be considered.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                    • djg
                      djg commented
                      Editing a comment
                      I meant a foam core/mold, fiberglass, then removing the foam. I can see my statement was very unclear. At least it was clear in my mind lol.
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