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Port Design Compromises

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  • #16
    For any vented designs I do I target <=17ms at rated power or xmax whichever comes first. For slot vents, keeping your ratio <1.0 to 10 helps prevent unwanted noises as well.

    In my opinion if your vent length needed starts to exceed 50”, you may want to seriously consider a Passive Radiator design or other alignment.

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    • #17
      If your vent length is more than 30 inches make the box larger, or use a smaller driver. Nothing good comes of using a port that's simply too long in the interest of using a box that's too small.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #18
        A 50" port does not sit well with me...

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        • #19
          My port choices right now ar 35-inch if the port is 1.5" high anf 41-inch if it is 1.75 inches high. Both options show first port resonance over 160Hz, so 80Hz xover should stil lbe ok. The 35-inch option will be L-shaped and the 41-inch option will need to be a folded port. Should I assume winisd is overestimating the effective port area and not considering the high-friction area near the port walls or do most people find it to be reasonably accurate?

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          • #20
            WinISD doesn't consider port wall friction. IME anything less than 2 inches will be problematic. I'd avoid a difference of only one octave from the top end of the pass band to the first port resonance. Two octaves is the minimum that I'd use.
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #21
              Originally posted by billfitzmaurice View Post
              WinISD doesn't consider port wall friction. IME anything less than 2 inches will be problematic. I'd avoid a difference of only one octave from the top end of the pass band to the first port resonance. Two octaves is the minimum that I'd use.
              I guess this is where those compromizes are going to come back into play. The design now has two ports that are 6.625-inch wide, 1.5-inch tall, and about 34-inch long. This puts first port resonance just over 200Hz. Two octaves above xover would be 320Hz. I don't think I am going to get there from here. I am still playing with options to increase the ports to 1.75-inch tall.

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              • #22
                Probably been mentioned already, but this is classic PR territory.
                Francis

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                • #23
                  Originally posted by pick View Post
                  I am still playing with options to increase the ports to 1.75-inch tall.
                  That's easy. Don't use slots.

                  www.billfitzmaurice.com
                  www.billfitzmaurice.info/forum

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