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Slotted port size

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  • Slotted port size

    I'm building floor standing speaker with a volume of 1.5 cu ft (8 3/4W x 28H x 10 5/8D)and using RS225-8 for woofer and RST28F-4 for tweeter tuned to 32hz. The recommended port size is 2" dia. by 4 inch length but I'm using a slotted port instead. I need help to compute for the slotted port dimensions. Thanks in advance for any help.​

  • #2
    I'll assume you're new (since I don't recognize you), so I hope those are your INside cab dimensions.
    For ME (personally), I'd use a 3" "Precision Port" w/a length of 12" (for a 30Hz tuning), and run it out the back (probably using an elbow).

    Typically, for YOUR box, you'd put the slot at the bottom and make the slot the interior width (I'll assume 8.75"), and probably an inch high. That gives you more area than even a 3" round port (for me, a 2" port w/an RS225 is too small). Since the area is more, it has to even be a bit longer. I'd go 16" (which means it'll need a fold or bend). For a 32Hz tuning, it'd be 13" long.

    You can model this yourself in WinISD ( ) by clicking the "shape" icon on the "port" tab.


    • #3
      Help questions really should go in the TechTalk sector. This is the Gallery for finished projects and photos.
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      • #4
        Thanks for the response, sorry if I post this in the wrong forum, this is my first post.


        • #5
          Originally posted by Chris Roemer View Post
          make the slot the interior width (I'll assume 8.75"), and probably an inch high.
          I seldom use ports less than two inches in any dimension. The region of high friction near the port wall extends at least a quarter inch from the walls, so an inch high port may act like it's only a half inch high. This is why narrow slots end up with lower Fb and higher port velocity than models predict.