Slot Port To Round Port Calculator

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. To calculate the slot width, divide 54.5 sq. By the height of 14.5 in. The result is 3.76 inches. Round that figure to nearest ¼ inch, and you get an offset measurement of 3 ¾ inch wide. The slot port would be 3 ¾ inches wide by 14 ½ inches tall. You don’t have to get too hung up on the box and port volume. 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.

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. Use the calculator on the 12volt. Just remember to use 14 - 16^in of port per cubic foot of air space (so 14 X net cubic feet). Multiply height times width of the slot port opening to get square inches. Input your width and height and net box volume and desired tuning freq and it will give you the required port length.

Comments

Port Area 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?