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  • Port size question

    I'm getting ready to embark on my first project. I have two Dayton Audio 5-1/4 Woofers (DC130BS-4) and two Dayton Audio tweeters (DC28FS-8). I want to make some bookshelf speakers but first I want to do some experimenting. I want to make one woofer cabinet that is sealed and .78 ft cubed and one ported at 1ft cubed. My problem (that I am aware of) is; I don't know how to figure out what my optimum port size should be.

    My goal in this project is to learn how to build some cabinets and hear how drivers can sound differently and play with different crossover levels to get the sound I'm looking for.

    Can somebody tell me how to figure out a good port size for this driver?

    Thanks,
    Jay

  • #2
    1st slight misconception which will become quickly apparent is that port calculators* are not directly dependent on driver data but rather internal volume and desired tuning frequency as part of a system response.

    * just 1 example:
    http://www.mobileinformationlabs.com...0lenth%201.htm
    The selection guide:
    http://www.parts-express.com/resourc...election-guide
    Suggests 72Hz
    "Not a Speaker Designer - Not even on the Internet"
    “Pride is your greatest enemy, humility is your greatest friend.”
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

    Comment


    • #3
      Originally posted by DRD2 View Post
      Dayton Audio 5-1/4 Woofers (DC130BS-4) ... one woofer cabinet that is sealed and .78 ft cubed and one ported at 1ft cubed. My problem (that I am aware of) is; I don't know how to figure out what my optimum port size should be.

      Can somebody tell me how to figure out a good port size for this driver?

      Thanks,
      Jay
      Those box dimensions (net internal for the woofer) are way to big for the DC130. And the DC130 really wants to be ported (not suitable for a sealed box).

      I'd go with a ported box of .36ft^3 tuned to 50 hz using a 5" port with an inside diameter of 1.61" (that's the inside diameter of 1.5" PVC pipe). That will give you an F3 in the lower 50hz range. But you'll have serious excursion issues when pumping a full 30w into that - I'd say 15w max and you're still exceeding xmax by a bit.

      DC130.jpg

      Comment


      • #4
        Also, look into WinISD (exactly what Mike used in the above screenshot). Modeling a woofer in a box is invaluable in making these kind of decisions, and the port dimension calculation is included.
        Electronics engineer, woofer enthusiast, and musician.
        Wogg Music
        Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

        Comment


        • #5
          Originally posted by wogg View Post
          the port dimension calculation is included.
          A port dimension is included, though not necessarily the best one. To get it right you need to model the cab with the expected maximum power input, make sure that the port velocity is between 15 and 20 meters/second. If the velocity is too high more port area is required, if less than 15 you can use a smaller port area to keep the cab size down.

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

          Comment


          • #6
            Originally posted by billfitzmaurice View Post
            A port dimension is included, though not necessarily the best one. To get it right you need to model the cab with the expected maximum power input, make sure that the port velocity is between 15 and 20 meters/second. If the velocity is too high more port area is required, if less than 15 you can use a smaller port area to keep the cab size down.
            Baby steps Bill! Jay was just at the "I'm going to build a box and see what happens" phase in speaker building
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music
            Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

            Comment


            • #7
              Originally posted by wogg View Post
              Baby steps Bill! Jay was just at the "I'm going to build a box and see what happens" phase in speaker building
              But he'd hardly be the first to use a port size that's fine for a 1w input and then wonder why it chuffs like mad with 100w. Just as you need to measure twice and cut once you need to model twice, or thrice, and build once.

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

              Comment


              • #8
                Great more info to keep me up at night. Seriously, this has taken off to be sort of an obsession and I have yet to make one cut or solder. Home brewing was my last hobby and I decided to get out of it for various reason. The similar thing I like about messing with speakers is the huge amount of variables that will affect the outcome. I can't wait to get started on a couple of boxes to see how they sound for myself.

                Thanks for the help!
                Jay

                Comment


                • #9
                  Originally posted by DRD2 View Post
                  Great more info to keep me up at night...
                  haha ( not worth loosing sleep over ).
                  Often the 2nd question is: "why not use the smallest port possible?" ( Mike tipped you off on that )

                  "Not a Speaker Designer - Not even on the Internet"
                  “Pride is your greatest enemy, humility is your greatest friend.”
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                  Comment


                  • #10
                    Originally posted by DRD2 View Post
                    Great more info to keep me up at night. Seriously, this has taken off to be sort of an obsession and I have yet to make one cut or solder. Home brewing was my last hobby and I decided to get out of it for various reason. The similar thing I like about messing with speakers is the huge amount of variables that will affect the outcome. I can't wait to get started on a couple of boxes to see how they sound for myself.

                    Thanks for the help!
                    Jay
                    Have you thought about building an existing design? There are many kits out there. Some have an available pre-cut baffle or an entire knockdown box to assemble. The kits that are for sale (some at PE, many elsewhere) were designed by Pros with years of experience. The designs have been validated many times (that's why they're for sale). And there are many choices for all budgets. You'd get the DIY feeling AND a great sounding speaker.

                    PE has the BR1 kit for ~$180 including cabinets that uses a 6.5" version of the DC series woofer and a similar tweeter. You could return the drivers you have to PE and just eat the shipping costs. You'll wind up spending the difference on crossover components and other "stuff" to complete a self designed unit anyway.

                    Note: I spent two years coming up speed on speaker design before I designed and built from scratch (I had a very specific need).

                    This 2-way FR graph accounts for Baffle Step and Diffraction ...

                    Click image for larger version

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                    Attached Files

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                    • #11
                      If you have time and wood to spare, I think there's great learning potential in building a couple crappy enclosures and observing how the speaker behaves in real life.
                      Electronics engineer, woofer enthusiast, and musician.
                      Wogg Music
                      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

                      Comment


                      • #12
                        Originally posted by wogg View Post
                        If you have time and wood to spare, I think there's great learning potential in building a couple crappy enclosures and observing how the speaker behaves in real life.
                        +1 I have done this exact thing...I still have 5 of those "crappy" enclosures in the garage, can't bring myself to just throw them away.
                        Paul

                        The "SB's" build page
                        http://techtalk.parts-express.com/sh...-4-(pic-heavy)

                        Comment


                        • #13
                          Originally posted by DRD2 View Post
                          I'm getting ready to embark on my first project. I have two Dayton Audio 5-1/4 Woofers (DC130BS-4) and two Dayton Audio tweeters (DC28FS-8). I want to make some bookshelf speakers but first I want to do some experimenting. I want to make one woofer cabinet that is sealed and .78 ft cubed and one ported at 1ft cubed. My problem (that I am aware of) is; I don't know how to figure out what my optimum port size should be.

                          My goal in this project is to learn how to build some cabinets and hear how drivers can sound differently and play with different crossover levels to get the sound I'm looking for.

                          Can somebody tell me how to figure out a good port size for this driver?

                          Thanks,
                          Jay
                          Hello from Australia
                          "
                          I haven't built them, but Curt Campbell's website has exactly what you're looking for: the " TriTrix MT" which use the same drivers and a ported cabinet, and a simple crossover. Many, many people have built and loved the Tritrix, maybe consider this option?

                          Geoff

                          Comment


                          • #14
                            I did a quicky model in a ported box with a net volume of 0.35 cubic feet. Using a port with a 2" ID and 6" length, the tuning frequency was ~56 Hz and f3 was ~52 Hz. An input of 10 watts created an output SPL of 98-99 dB (not counting baffle step losses) with the driver exceeding Xmax at all frequencies below ~49 Hz and with the peak air velocity in the port of ~10 m/s at 50 Hz.
                            Paul

                            Comment


                            • #15
                              Originally posted by Geoff Millar View Post

                              Hello from Australia
                              "
                              I haven't built them, but Curt Campbell's website has exactly what you're looking for: the " TriTrix MT" which use the same drivers and a ported cabinet, and a simple crossover. Many, many people have built and loved the Tritrix, maybe consider this option?

                              Geoff
                              Great eye ...

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