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What software for modelling vented boxes?

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  • What software for modelling vented boxes?

    I am doing a custom version of the Saffrons. Instead of a small chamber for 1 woofer and a larger ported chamber for the 2nd, I am putting both woofers into a 34 litre (1.20 ft3) vented box tuned to about 50hz. I just want to find out if a 2" diameter port is large enough.
    What is the simplest option?

  • #2
    WinISD. Will get you close. Always have to prototype, test, measure,

    Comment


    • #3
      Hello from Australia

      I'm not sure if putting this design in one cabinet will work: the designers' write up says: (http://projectgallery.parts-express..../the-saffrons/)

      "The low frequency woofer is allowed to dig just about as deep as it can without falling apart, and the mid-woofer is choked down on the low end by the enclosure volume" and "as long as the volumes are maintained, rectangular enclosures should be quite adequate" - I read this as saying you can use one cabinet but divided internally. Is that what you were thinking? One portion (upper woofer) would be sealed, the other (lower) vented.

      If so, and the volume of the cabinet for the second woofer is the same as the original design, why not use the same port spec? Perhaps other PETT members who know much more than I do about these things could comment, I'm happy to be proved wrong.

      HTH

      Geoff

      Comment


      • #4
        Originally posted by tvrgeek View Post
        WinISD. Will get you close. Always have to prototype, test, measure,
        Someone tree'd grumpy Roemer with WinISD, but crop dusted him with prototype, test, measure (a great suggestion BTW)
        Craig

        The lowest possible F3 box alignment is not always the best alignment.

        Designing and building speaker projects are like playing with adult Lego Blocks for me.

        Comment


        • #5
          If someone could double check my simple calculation.
          A 34 litre box could be tuned to 50hz with a 3" round port 4.16" long?

          Comment


          • #6
            Originally posted by Geoff Millar View Post
            Hello from Australia

            I'm not sure if putting this design in one cabinet will work: the designers' write up says: (http://projectgallery.parts-express..../the-saffrons/)

            "The low frequency woofer is allowed to dig just about as deep as it can without falling apart, and the mid-woofer is choked down on the low end by the enclosure volume" and "as long as the volumes are maintained, rectangular enclosures should be quite adequate" - I read this as saying you can use one cabinet but divided internally.

            I also thought of building these as they had won the Best Iron Driver competition and I had the 830656 drivers, but with my level of skill I couldn't really understand the crossover and it has a lot of parts, which made it costly in Oz.

            I then looked at the 2012 winner, which also used the 830656. It was an MTM using the XT25 tweeter, but that was expensive here, so I eventually built Ron E's "C-notes"MTMs, which are detailed on PETT. They're 1.2 cu ft and came a very close second: they sound very good!

            The XT25 design is also detailed on PETT, I'll find the links and post them if you wish. It used a slot port, from memory.

            Geoff
            I am aware how he did it, I just want to get some more output in the sub 80hz range. 34 litre boxes already assembled.

            Comment


            • #7
              Originally posted by PWR RYD View Post

              Someone tree'd grumpy Roemer with WinISD, but crop dusted him with prototype, test, measure (a great suggestion BTW)

              love the drag race reference!

              seems he was busy eating at Gapplebees!

              Comment


              • #8
                Originally posted by ontariomaximus View Post

                I am aware how he did it, I just want to get some more output in the sub 80hz range. 34 litre boxes already assembled.
                OK, just thought I'd ask the question.

                You could check out these cabinets; one is 34l, the other 35l ; the first has a slot port, the second a tube. Not sure if they would work for you in terms of low end output.

                http://techtalk.parts-express.com/forum/tech-talk-forum/53042-iron-driver-overall-best-sounding-speaker-design-details
                http://techtalk.parts-express.com/forum/tech-talk-forum/53050-c-note-iron-driver-build

                Geoff

                Comment


                • #9
                  Originally posted by Geoff Millar View Post

                  OK, just thought I'd ask the question.

                  You could check out these cabinets; one is 34l, the other 35l ; the first has a slot port, the second a tube. Not sure if they would work for you in terms of low end output.

                  http://techtalk.parts-express.com/forum/tech-talk-forum/53042-iron-driver-overall-best-sounding-speaker-design-details
                  http://techtalk.parts-express.com/forum/tech-talk-forum/53050-c-note-iron-driver-build

                  Geoff
                  I saw those years ago LOL. I have had the parts for this project kicking around for a number of years. The six drivers, all the crossovers, and a note that said 34 litres net, tuned to 49.8hz and an F3 of about 48hz (pair of 830656's). Can't even remember what I used to calculate that, and WINisd is showing me something a bit different.

                  Comment


                  • #10
                    Originally posted by ontariomaximus View Post

                    I saw those years ago LOL. I have had the parts for this project kicking around for a number of years. The six drivers, all the crossovers, and a note that said 34 litres net, tuned to 49.8hz and an F3 of about 48hz (pair of 830656's). Can't even remember what I used to calculate that, and WINisd is showing me something a bit different.
                    Some years ago I saw a project for a MLTL for the 830656 (single driver) which gives a stated F3 in the low 30s and not very efficient: - 84dB, so it looks like you can persuade that driver to get quite low. No idea how that could be adapted to your project, I'm afraid.

                    Good luck

                    Geoff

                    Comment


                    • #11
                      Originally posted by ontariomaximus View Post
                      If someone could double check my simple calculation.
                      A 34 litre box could be tuned to 50hz with a 3" round port 4.16" long?
                      Hi Ontario. Let me begin by pointing out that you did not link to the Saffrons or specify what drivers they are. However, Geoff provided the link and I happen to be building something with these woofers.

                      With two drivers in 34 L and tuned to 50Hz I get a 3" port at 4.12" long. So you seem to be spot-on.
                      The transfer function I get is below.

                      Click image for larger version

Name:	34L 50Hz temp.PNG
Views:	132
Size:	129.5 KB
ID:	1447131


                      Comment


                      • #12
                        I started designing speakers long before modeling software became available. I use the charts provided in Vance Dickason's Loudspeaker Design Cookbook. I physically measure all required Thiele/ Small parameters with my test equipment and signal generators. Hard to break old habits when they work just fine. Never trusted published specs.

                        Comment


                        • #13
                          Originally posted by Regore View Post
                          I physically measure all required Thiele/ Small parameters with my test equipment and signal generators. Hard to break old habits when they work just fine. Never trusted published specs.
                          Definitely agree on measurement, lots of measurements are significantly different than manufacturers specs. On the other hand, trash the charts because the software is so good IF you give it good inputs.
                          My T/S parameters for the WinISD sim above is based on the average of measurement for 4 drivers, except VAS which I used mfg specs. (I didn't even realize I wasn't using mfg specs until your post and I went to check. I must have measured these awhile ago because I didn't even remember that I had.)

                          My measurements are below.

                          Click image for larger version

Name:	830656 TS measurements.PNG
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Size:	19.6 KB
ID:	1447135

                          Comment


                          • #14
                            Originally posted by a4eaudio View Post

                            Hi Ontario. Let me begin by pointing out that you did not link to the Saffrons or specify what drivers they are. However, Geoff provided the link and I happen to be building something with these woofers.

                            With two drivers in 34 L and tuned to 50Hz I get a 3" port at 4.12" long. So you seem to be spot-on.
                            The transfer function I get is below.

                            Click image for larger version

Name:	34L 50Hz temp.PNG
Views:	132
Size:	129.5 KB
ID:	1447131

                            I think I need to lower the tuning to 40-41hz. Seems to be a pretty large bump with 50. But high qts does that.

                            Comment


                            • #15
                              Knowing that the woofer was the Iron Driver back when the Saffron won and the Ron E.'s C-Notes were widely praised I tried to keep a record of what everyone did. I figure I trust a bunch of people actually listening to speakers built by people who know what they are doing than just simulating in WinISD. I'm still in the planning stage but my target for two drivers is 28L tuned to 44Hz although I don't remember how I came up with this.

                              Edit: If you look up Ron_E's C-notes he ended up changing the tuning to 36Hz and liked it better, but I don't remember what is box volume was off hand.

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