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Question About Porting

Discussion in 'Amps and Cabs [BG]' started by SurferJoe46, Mar 7, 2010.

  1. Does the cabinet tuning freq change or is it eliminated by the ports?

    Will ports not make the square footage/inches go infinite and have little or no effect perhaps like an open-backed cab?
  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I have to be a bit careful with terminology here. A ported speaker effectively has two tuning frequencies. One is determined by the cone and the box, the other by the port and the box. The cone / box resonant frequency stays the same if you make the box sufficiently bigger to provide for the volume taken up by the port.
  3. O K --------------------- >

    Let me ask about this part then:

    How do the ports "take volume" from the box? Are they considered intrusive and therefor have to have compensation for their size or is it more along the lines of bouncing/colliding sound waves that don't exist as they did before porting?

    Do you understand my question?
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The tuning frequency (Fb) is determined exclusively by the box and port dimensions. Different drivers don't affect it.

    When a box program gives a box volume (Vb) it is a net internal volume exclusive of the driver and ducts.
  5. That make sense to me now. I was trying to envision what the ports do to the overall volume, and I see that it hasn't changed in actuality.

    Vb then is a constant and is set by the box internal dimensions - but you also said "net internal volume" so that still leave me in suspense - a little.

    Is there not then a subtractive factor for the vents/ports?

    I'm never gonna build a box/cab or enclosure - but I find this very interesting.
  6. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    The term "exclusive of driver and ducts" means you do NOT count them in the interior volume. The port structure and open "duct" don't get counted; you calculate their size and subtract that from what you've got. You make the box bigger if necessary.

    Calculating the size of the driver itself is a bit harder because it's conical. But manufacturers should make that info available.
  7. xk49w


    Apr 13, 2008
    Not really. The box has an associated volume, the tube (port and its length) another. Perhaps it is easiest to picture the tube as extending completely outside the box. It is only the construction geometry that makes the tube appear to be inside the box.
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Yes. That's why I was trying to be careful about terminology. Like you say, Fb is determined by the box and port. I wanted to differentiate that from the resonant frequency of the driver cone in the box.
  9. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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