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  • Anybody care to model a transmission line?

    It would be nice to have a single box modeling tool that would allow you to quickly flip between sealed, vented, PR or T-line box configurations of the same or different sized boxes and that would model the frequency response, maximum SPL, excursion impedance, etc. The equations for sealed, vented and passive radiator are well documented and are mature, but according to the study in the link, the transmission line models so far are inadequate. However, the author outlines a more complete model that someone might be able to integrate into a comprehensive box modeling tool.

    Any takers?

    http://smartech.gatech.edu/bitstream...200705_phd.pdf

    Click image for larger version

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    :D
    Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

  • #2
    Re: Anybody care to model a transmission line?

    You don't ask for much huh? No help here; just couldn't help but comment.
    ~Mark

    Stuff I've builded http://techtalk.parts-express.com/co...lies/smile.png

    Comment


    • #3
      Re: Anybody care to model a transmission line?

      With sufficient skill you can model a basic TL in HornResp, though it won't do reverse taper.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

      Comment


      • #4
        Re: Anybody care to model a transmission line?

        I'm printing it out and I'm actually going to look into it. Just flipping through, it looks extremely thorough... and unfortunately it's been close to a decade since I've done any "real" math, but I may try turning it into code.

        I'm sure the bigger issue here is getting permission from the author to use his work for either a commercial or open-source project like this.

        Comment


        • #5
          Re: Anybody care to model a transmission line?

          Originally posted by Jason View Post
          I'm printing it out and I'm actually going to look into it. Just flipping through, it looks extremely thorough... and unfortunately it's been close to a decade since I've done any "real" math, but I may try turning it into code.
          Cool. There has been some recent work done in VB.net that would make an integrated box program fairly easy, but someone would need to get that T-L model working. That graphic that was in the original post actually has quite a bit of code behind it, although most of it belongs to someone else who frequents this board. So I thought I would do some trolling to see if anyone would bite...

          Bullock and White have an old DOS program that implements a T-L model of some sort (see http://users.hal-pc.org/~bwhitejr/ ). MJ King used to have a model that appears to be based on the work of Bradbury and Augspurger, although the MathCAD code is no longer available (http://www.quarter-wave.com ). So it's been done before, and there is a fair amount of documentation available. Robinson claims to have developed a more accurate model for the fill material, so his work is interesting, although his model doesn't address tapered lines.

          Originally posted by Jason View Post
          I'm sure the bigger issue here is getting permission from the author to use his work for either a commercial or open-source project like this.
          You may be right, but I don't think you can patent or copyright mathematical models. Code can be copyrighted, and a method or process can be patented, but I think models are different. Of course, we could always ask anyway...
          Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

          Comment


          • #6
            Re: Anybody care to model a transmission line?

            Originally posted by neildavis View Post
            It would be nice to have a single box modeling tool that would allow you to quickly flip between sealed, vented, PR or T-line box configurations of the same or different sized boxes and that would model the frequency response, maximum SPL, excursion impedance, etc. The equations for sealed, vented and passive radiator are well documented and are mature, but according to the study in the link, the transmission line models so far are inadequate. However, the author outlines a more complete model that someone might be able to integrate into a comprehensive box modeling tool.

            Any takers?

            http://smartech.gatech.edu/bitstream...200705_phd.pdf

            [ATTACH]2112[/ATTACH]

            :D
            Martin King has been offering Mathcad files that work quite nicely for modeling a variety of TL configurations.

            Lots of successful designs based on those models, and they predict reality very well.
            http://www.quarter-wave.com
            R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
            Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

            95% of Climate Models Agree: The Observations Must be Wrong
            "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

            Comment


            • #7
              Re: Anybody care to model a transmission line?

              Rumor has it that the real woofer tester folks are working on one. If that's true, I can't wait to try it.

              Bill

              Originally posted by neildavis View Post
              It would be nice to have a single box modeling tool that would allow you to quickly flip between sealed, vented, PR or T-line box configurations of the same or different sized boxes and that would model the frequency response, maximum SPL, excursion impedance, etc. The equations for sealed, vented and passive radiator are well documented and are mature, but according to the study in the link, the transmission line models so far are inadequate. However, the author outlines a more complete model that someone might be able to integrate into a comprehensive box modeling tool.

              Any takers?

              http://smartech.gatech.edu/bitstream...200705_phd.pdf

              [ATTACH]2112[/ATTACH]

              :D
              The first one through the wall always gets the bloodiest...

              Comment


              • #8
                Re: Anybody care to model a transmission line?

                Martin King has been offering Mathcad files that work quite nicely for modeling a variety of TL configurations.

                Lots of successful designs based on those models, and they predict reality very well.
                http://www.quarter-wave.com
                "Please Note :

                In November 2008, I stopped providing access to my MathCad worksheets. Support from the DIY community was weak and I was having too many problems with unlicensed commercial ventures using the worksheets. The restricted page is still available for current license holders until their agreement expires, then the page will be removed completely.

                Recently, I have been receiving several e-mails per day requesting a license and/or access to the worksheets. Unfortunately, I cannot accommodate these requests. I have made this difficult decision and I do not see it being reversed. My apologies for any inconvenience but I just could not continue using this method of distribution and access."

                Comment


                • #9
                  Re: Anybody care to model a transmission line?

                  Originally posted by Jason View Post
                  "Please Note :

                  In November 2008, I stopped providing access to my MathCad worksheets. Support from the DIY community was weak and I was having too many problems with unlicensed commercial ventures using the worksheets. The restricted page is still available for current license holders until their agreement expires, then the page will be removed completely.

                  Recently, I have been receiving several e-mails per day requesting a license and/or access to the worksheets. Unfortunately, I cannot accommodate these requests. I have made this difficult decision and I do not see it being reversed. My apologies for any inconvenience but I just could not continue using this method of distribution and access."
                  Well, that is a shame. they were quite excellent pieces of software.
                  R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                  Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                  95% of Climate Models Agree: The Observations Must be Wrong
                  "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                  Comment


                  • #10
                    Re: Anybody care to model a transmission line?

                    Originally posted by Jason View Post
                    I'm printing it out and I'm actually going to look into it. Just flipping through, it looks extremely thorough... and unfortunately it's been close to a decade since I've done any "real" math, but I may try turning it into code.

                    I'm sure the bigger issue here is getting permission from the author to use his work for either a commercial or open-source project like this.

                    Isn't a phd thesis public domain (education for the greater good)?

                    Regardless, to protect that sort of IP you would need patents. A copyright only protects the written document from being copied or used un-cited. Actually applying the ideas doesn't constitute copyright infringement and without patents for applications of the work there is obviously no patent infringement. I think it would be hard to patent the transmission line speaker enclosure in and of itself due to prior art.. but the US patent office is a mystical magical place where all sorts of strange things happen.

                    Comment


                    • #11
                      Re: Anybody care to model a transmission line?

                      I actually translated one of his old Mathcad sheets into something more user-friendly with a simplified user interface, but A) since it's his work and he obviously is protective of it and B) it's an old model and not particularly accurate, I've kept it to myself as an "educational exercise".

                      I'm currently reading through the paper to see if it actually provides adequate documentation to code something from. There's a little blurb in the conclusion that has me a little skeptical that there will be adequate information to do "elaborate" TL designs:
                      The empirical formulas for the line parameters given in Sections 4.4.4 and 4.4.5 allow the design of a fiberglass-filled line to be evaluated by adjusting three parameters: the line length, the line diameter, and the fiber packing density. In further applications, more detailed experimental data is required to better characterize the fiberglass and its associated parameters over a wider range of tube diameters and packing densities. The empirical equation obtained for the flow resistance has the same form as those given in [9], [16], and [14]. By varying the line length, the line diameter, and the fiber packing density, the effects of each parameter on sound pressure level radiated by the driver, the tube, and system can be easily studied using mathematical software. The evaluation can also be performed with electrical circuit simulator software.

                      In addition to modeling the simple transmission line system that has the loudspeaker mounted at one end of the line, the model can be adapted to model two other popular types of transmission line systems. By placing a transmission line load on both the front and back sides of the loudspeaker, a transmission line system having a recessed loudspeaker can be analyzed. An acoustical compliance in parallel with the line can be used to model a coupling chamber between the loudspeaker and the line. It is believed that the model can be extended to account for tapered or flared lines by using techniques found in [38] that apply to acoustical horns.
                      So without having read the entire paper, it would seem that it deals strictly with a line of "constant radius" - i.e. no taper. The cited reference [38] is a paper by Leach on a model for acoustical horns, which would probably have to be studied to determine how much effort would be required to extend the presented model to tapered/flared lines.

                      Comment


                      • #12
                        Re: Anybody care to model a transmission line?

                        I have always wanted to build one dezzzz. Yes they are horns but still cool and ready for 15"s.

                        http://www.decware.com/imperial.htm

                        http://www.decware.com/ImperialSO.htm


                        Man are they monsters.


                        HT-EXT

                        Comment


                        • #13
                          Re: Anybody care to model a transmission line?

                          Originally posted by HT-EXT View Post
                          I have always wanted to build one dezzzz. Yes they are horns but still cool and ready for 15"s.

                          http://www.decware.com/imperial.htm

                          http://www.decware.com/ImperialSO.htm


                          Man are they monsters.


                          HT-EXT
                          Horribly obsolete. They were great cabs 50 years ago, but that was then...
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

                          Comment


                          • #14
                            Re: Anybody care to model a transmission line?

                            The past is what has helped us build better for the future.

                            HORRIBLY OLD SCHOOL COOL !!!


                            HT-EXT

                            Comment


                            • #15
                              Re: Anybody care to model a transmission line?

                              Originally posted by Jason View Post
                              So without having read the entire paper, it would seem that it deals strictly with a line of "constant radius" - i.e. no taper. The cited reference [38] is a paper by Leach on a model for acoustical horns, which would probably have to be studied to determine how much effort would be required to extend the presented model to tapered/flared lines.
                              That's true--the model in the paper only addresses constant-radius T-L's. However, the model is developed as two lines with coupling between them: the acoustical model of the air and the mechanical line with the fiberglass. So by replacing the acoustical model with the horn model, it should be possible to extend the model to tapered or flared lines. But that's probably a lot of work. The Leach paper is at: http://users.ece.gatech.edu/~mleach/papers/hornmod.pdf

                              I had assumed that horns would be best modeled using a separate program because of the large number of variables that are typically required to specify the design. However, it is clear to me now that tapered T-L's cross the boundary into horn design. So maybe the idea to develop a single box modeling tool that could deal with everything from sealed boxes to T-L's isn't such a good idea. I probably need to play with that Leach PSPICE code to make up my mind.
                              Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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