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The 'Minimum Port Area Required' result is how much port area you will need to keep port velocity under about 30 meter per second for slot ports and 32 meters per second for aero (or other round) ports. Port velocities above these numbers are where serious port compression sets in. No, what you'll need to do is figure the area. 2' dia cirlce is 3.14 in. (the R of a 2' circle is 1, so 1 squred is 1. pie (3.14) = 3.14 sqaured.) SO you would need a 1 x 3.14 slot at whatever leangth. Same leangth as the round port. Port tube length calculations for round ports: input = Radius of Port (R), tuning frequency in Hz (fb), Volume of the box in cubic inches (Vb), (L) will be the resulting length of tube. To figure your port, square/slot/round and different tunings for your box, try here. Select Loudspeakers-101 and then check fro that menu (design port/s) and click on that. Some very basic info is given, and a calculator is their for giving you the deminsions you'ed need for a particular tuning using round, square or slot port/s. Port Length Calculator. Online Port Length calculator helps to determine the length port size for sub woofer box design.

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Slot Port To Round Port Calculator Cubic

L Slot Port Box Calculator

• edited February 2019

  I always use winISD to convert. Adjust the tuning to match your 3' X 3.65' then select square port and enter your target height and width to get the length. Online calculator can do the same thing. http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm
• How about a spreadsheet from our friend Paul Carmody?
  

  HTH

  Jim
  
• As Wolf posted: Pi x r^2 = L x W so:
  3.1415 × (1.5')^2 = 7.068 in^2 (~ 7 sq in)
  If your slot port width is 7', then the slot port height would be
  7 sq in / 7' = 1' (7' wide x 1' high)
  Or
  7 sq in / 3.5' = 2' (3.5' wide x 2' high)
  Etc
• the area of the slot port should be the same as the area of the round port. Keep the length same.
  If you want to really optimize, usual the round ports are in the center away from the walls, whereas slot ports use the walls as one of the side - this does affect the lenght of the port for a particular tuning - Jeff B has a formula for calculating how much of the lenght should be altered if you are near a wall rather than away from a wall (at least twice the diameter of the port... Or just skip it, you will be in the ball park

• The other rule of thumb was to keep the height to width ratio no more than 1 to 7, (1 to 9?)

  I can't remember the exact end correction/ boundary factor for the slot port, but I've used port length -1 port height multiple times and been very close to the box model.

  John H, thanks to JP I did get that email
• Thanks for the answers, all. They've helped clear up the concept.
  
• Pretty sure that is 1 to 8 ratio. Rory relayed that info.
• Here's a picture that shows how the K value changes with slot port location. It was taken from this PETT thread: http://techtalk.parts-express.com/forum/tech-talk-forum/66368-q-slot-port-length.
  
• How are these calculations or examples affected when a speaker has those old fashioned slot vents sometimes found on early speakers? I'm referencing my old EV speakers that have roughly (4) 1/4' wide by 10' vents, 3/4' deep on the back of the cabinet. Was there a specific purpose for those vents, as opposed to a single vent of round or rectangular shape? Can the above vents shown by Ed Perkins be used if you desired to seal up the back of such a speaker?