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Port sizing...

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  • Port sizing...

    Which diameter 'works best' for a given woofer? Where is it written that a 3in port goes with 10in woofer, 6in goes with 15-18in woofers?? Thanx for a little advice in this regard.....

  • #2
    It's more about the port velocity at the anticipated power level. This is a combination of the drivers xmax, sd, and power applied vs the port area. The higher the output the more port area you will need to avoid chuffing.

    Typically I will use a 1.25" port for a 4" driver, 1.5" for 5", 2" min for 6.5, 2.5 to 3" for 8", 3" min for 10" 4" for 12 , and (2) 4" for a 15. General guideline. I will of course adjust for greater xmax, multiple drivers, etc.


    • #3
      It's not written like that anywhere. Port Mach has to do with tuning frequency, port diameter and length that result from that frequency, intended power level and output level, as well as the driver sensitivity and xmax usage at said levels and tunings. It really isn't something cut and dried.

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      • #4
        Originally posted by stargate69 View Post
        ...Where is it written that a 3in port goes with 10in woofer, 6in goes with 15-18in woofers??.....
        Not here

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        • #5
          It's a balancing act. What you're describing is a VERY general rule of thumb. Obviously, the larger the woofer, the more air it will move. So it would be nice to have a wide port. However, the larger diameter the port, the longer you need to go for the same tuning. The smaller diameter the port, the shorter you can make it, which would seem ideal. But then you run into issues with port noise. So these guidelines give you the (general) minimum size for a reasonable length with minimal port noise. The details of the design determine everything (as Wolf pointed out above).

          As I said these are rough guidelines. There are designs that break these "rules" and designs that accept trade-offs. If you don't listen at loud volumes, you'd be able to get away with a smaller diameter port, as you'll never reach XMax.

          BTW, in the above stickies, you'll find a thread called The Speaker Building Bible. It's a great read that contains answers to many of the questions you'll have ...


          • #6
            What size woofer are we talkin' here? In MY book, it says to divide the woofer's dia. by 3.
            A 3"id port tube will work well enough IF you can fit it in the box. IF it won't fit (and you don't want to do a "slot" or pay out for a passive radiator) then a 2-1/2" (or even a 2") MIGHT work, IF you don't turn it up enough to "chuff". If that 8"er has high Xmax (like, maybe over 6-8mm) and you intend to USE it, then you'll have to at LEAST "roundover" the port ends, or go w/a 3" "Precision Port" (flared ends), our go up to even a 4" (which gets easier to do if your box is larger, like, say, 3cf or more.