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How to Calculate Bass Reflex Cabinets

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  • How to Calculate Bass Reflex Cabinets

    Can someone give me the quick and easy way to calculate

    - port length given the diameter/area of the port, box volume, and desired frequency

    - does the length of port halve or double when you use two ports

    - how to calculate slotted ports

    - do port(s) take away from the volume of the cabinet? Does the cabinet need to increase in volume proportionately to the volume the port takes up?

    -minimum port size for 15” drivers, minimum for 18”, multiple ports or just design a slotted port?

    - was thinking of using a Dayton PA460-8 18” woofer in a 9cuft box tuned to 32hz. What size ports should I use? 4”, 5”, 6”? Double ports? Slotted port.

    thanks in advance

    YO

  • #2
    Easiest way IMO is WinISD.

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    • #3
      Can't you use WinISD ( from linearteam.org )?
      If you double the area, the length (basically) doubles. WinISD has an "online" vers (in case you've got a Mac).
      For the most part, a slotted port with the same area (as a round port) will have pretty much the same length for the same tuning. Again, ...
      yes, and yes
      For a 15" I'd go no less than 5" id. (A pair of 4"ers could work). 6"id for an 18". Besides slots, you can use passive radiators.
      Three 4"ers, each 8" long would make that tuning.
      You COULD go smaller (8cf) w/a higher tuning (high 30s) w/three 4" ports, each 6" long.
      The possibilities are endless.

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      • #4
        Chris Roemer , thanks for the info. I will have a look at WinISD. I’m trying to build a Klipsch Cornwall clone, but use an 18” instead of a 15”. Like the look of slot ports, I may ask your advice to review the design when the time comes closer. Thanks again
        YO

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        • #5
          LOL... EYE started a stop watch on my phone, guessing how long it would take for Grumpy Roemer to post an ad for WinISD. EYE lost my own bet. EYE GUESSED 60 minutes. It ACTUALLY took 70 minutes.
          Craig

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          • #6
            Originally posted by PWR RYD View Post
            LOL... EYE started a stop watch on my phone, guessing how long it would take for Grumpy Roemer to post an ad for WinISD. EYE lost my own bet. EYE GUESSED 60 minutes. It ACTUALLY took 70 minutes.
            I was thinking Unibox but I've been out of the speaker building game long enough that there might be newer options available...
            "I like Brewski's threads, they always end up being hybrid beer/speaker threads based on the name of his newest creation." - Greywarden

            Breakfast Stout - HiVi RT2 II/Aurasound NS6
            Imperial Russian Stout - Vifa DX25/Fountek FW146/(2) Fountek FW168s - Built by Fastbike
            Ruination 2.5 way - Vifa DX25/Fountek FW168
            Levitation TM
            - Vifa BC25SG15/Fountek FW168

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            • #7
              Horn Response is awesome as well, and has advanced modeling that can be utilized. Akabak can also do a lot, but it's too time-consuming for most. There is always BassBox, I think that is still around. Heck I even have copies of Bullock's Box Model and BP Box model for Win95. Those were the days.

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              • #8
                Another vote for WinISD. The Pro version is my favorite. I guess I'm in the bag, too
                Francis

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                • #9
                  These are the ones that I have saved:

                  WinISD Alpha Pro:



                  Win ISD:

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                  • #10
                    The lowest F3 possible is KING.... just joking.
                    Craig

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                    • #11
                      Originally posted by Brewski View Post

                      I was thinking Unibox but I've been out of the speaker building game long enough that there might be newer options available...
                      UniBox (which is my go to program) doesn't do slotted ports AFAIK. WinISD is the program that checks all the boxes on the OP's list.
                      Failure is not an option. It comes bundled with Windows.

                      We are passionate about great sound at whatever level we can afford, so don't let the audio atheists reduce the experience to a set of numbers and squiggly lines. - jbruner

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                      • #12
                        for Craig

                        (from Alden/Dickason) if: R=port radius in inches, Fb=tuning freq. of box, Vb=volume of box in cu.ft.
                        then port length in inches = R^2 x 8466 / Fb^2 / Vb - Rx1.46

                        (from Weems/Keele) this equation calcs the "vent area : length" ratio (Ra) to tune a given size box (Vb, in cu.ft.) to a given freq. (Fb)
                        Ra = Fb^2 x Vb / 2702
                        then vent length (inches) = vent area(sq.in.)/Ra - 0.83 x sq.rt.(vent area)

                        For a 9 cf. box tuned to 32Hz with a 6"id port:
                        Dickason
                        3^2 x 8466 / 32^2 / 9 - 3x1.46 =
                        9 x 8466 / 1024 / 9 - 4.38 = a port length of 3.9"

                        Keele
                        Ra = 1024 x 9 / 2702 = 3.41
                        9x3.1416/3.41 - 0.83x5.32 = 8.29-4.41 = a port length of 3.9"

                        (WinISD 0.50a7 calcs 3.84")

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                        • #13
                          Chris Roemer thanks for the infos!! Would two 5” be 8” long?
                          YO

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                          • #14
                            Originally posted by PWR RYD View Post
                            LOL... EYE started a stop watch on my phone, guessing how long it would take for Grumpy Roemer to post an ad for WinISD. EYE lost my own bet. EYE GUESSED 60 minutes. It ACTUALLY took 70 minutes.
                            Gave yourself a black EYE.

                            Comment


                            • #15
                              yup

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