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How much clearance for bottom port

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  • How much clearance for bottom port

    So my simulation on my latest project are saying I need 8.25" port length. My box is not that deep. I have three choices as I see it.

    1. L shaped port
    2. Port on the top
    3. Port on the bottom
    How much clearance would I need for the bottom?
    Just another hobbyiest.

  • #2
    Approximately the diameter of the port. You can go smaller, but you're tuning frequency will be affected a bit.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music
    Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

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    • #3
      I put some screen around the bottom to make it easier to dump out stuff that "falls" in there.

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      • #4
        The proximity of the port to the cabinet wall and floor can increase the effective length of the port. If you have the ability to measure the tuning you can make adjustments as you go. I also did a project where the port exited the bottom of the cabinet and I used the space under the cabinet to extend the length of the port.
        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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        • #5
          So let me clarify. Not internally but externally. So if the port opening were on the bottom of the box.
          Just another hobbyiest.

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          • #6
            If you had a port with a 2" internal diameter then you would want to have 2" tall feet on the bottom of your enclosure.
            Craig

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            • #7
              I've always wanted to do bottom ported, just so I could use that cool cone-shaped aerodynamic device that I've seen used.
              Francis

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              • #8
                Originally posted by PWR RYD View Post
                If you had a port with a 2" internal diameter then you would want to have 2" tall feet on the bottom of your enclosure.
                To use the bottom of the cabinet and stand top as the port I calculated the same area as the port, like a slot port and ended up with 1/2 inch feet for my 1-3/8 inch port tube. That was probably a bit higher than needed, but I was able to adjust the inside port tube to get the tuning I wanted.
                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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                • #9
                  Originally posted by fpitas View Post
                  . . . . cone-shaped aerodynamic device that I've seen used.
                  POLK Audio Power Port.

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                  • #10
                    Originally posted by AEIOU View Post

                    POLK Audio Power Port.
                    Thanks! Whatever the pros and cons of bottom porting, I've always liked the look of that thing.
                    Francis

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