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Midwest Audio Fest

It’s that time audio enthusiasts!

Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project.
We are excited to see all returning participants, and look forward to meeting some new designers this year, as well!

Be sure your plans include a visit to the Parts Express Tent Sale for the lowest prices of the year, and the Audio Swap Meet where you can buy and trade with other audio fans.

We hope to see you this summer!

Vivian and Jill
2 of 2 < >

Midwest Audio Fest

It’s that time audio enthusiasts! Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project. We are excited to see all returning participants, and look forward to meeting some new designers this year, as well! Be sure your plans include a visit to the Parts Express Tent Sale for the lowest prices of the year, and the Audio Swap Meet where you can buy and trade with other audio fans. We hope to see you this summer! Vivian and Jill
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Transmission Line, MLTL software

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  • Transmission Line, MLTL software

    I have built several speakers over the years and I would like to do something a little different. I was thinking about a Transmission Line. Since Martin King's software is no longer available is there a suitable replacement?

  • #2
    https://www.parts-express.com/dayton...-pair--300-658

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    • #3
      Originally posted by grubby65 View Post
      I have built several speakers over the years and I would like to do something a little different. I was thinking about a Transmission Line. Since Martin King's software is no longer available is there a suitable replacement?
      AFAIK you can still purchase his spreadsheets for $25. The user group is below where you can ask. You'll need to download a free version of MathCad 8 to use the spreadsheets.
      "Everything is nothing without a high sound quality." (Sure Electronics)

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      • #4
        Unfortunately, I ended sales of the worksheets through the Yahoo Group at the end of the year. There was almost no interest in the last 9 months of 2018 so it was time to call it quits.

        The Yahoo Group will also be closing and is being replaced by two Facebook groups. These new groups are linked from the homepage on my website.
        Martin

        Quarter Wavelength Loudspeaker Design
        www.quarter-wave.com

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        • #5
          Unless you really want to design your own cabinet, and depending on your budget , room size and music tastes, why not go for an existing design which you know will sound good? There are quite a few designs out there:

          Curt Campbell's Tritrix MTM TLs have many, many happy users, as do his Aviatrix, although their RS28F tweeter is nla;

          speakers by well recognised TL designers such as Paul Kittinger, whose designs (you'll find some in the PE Project Gallery) have won awards at various audio events.

          Also, a PETT member built a MLTL cabinet for Paul Carmody's Overnite Sensations MTM.

          There are many older designs available, but in most cases their drivers are out of production.

          I find this a fascinating subject, but one look at the spread sheets, calculations etc involved in designing a cabinet that would sound right encouraged me to ask the experts!

          Hope this helps

          Geoff

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          • #6
            My workbooks at https://www.diysubwoofers.org/sheets/ and Hornresp can probably do what you want, but you'll have to become familiar with using Hornresp :-).

            The workbooks allow you to come up with a physical layout using one sample layouts, and then produces a Hornresp import file that allows you to model the results in Hornresp. When looking at the sim using Hornresp's "Loudspeaker Wizard", you can made modifications to the physical layout of the MLTL in the workbook, Export and then press F6 in Hornresp to update the sim.
            Brian Steele
            www.diysubwoofers.org

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            • #7
              Interesting. Designing a small TL to have a play and use up a pair of drivers I bought but didn't use is near the top of my todo list. If there isn't any design software around that would be interesting and something I might be able to address. Is this the case? Is Martin intending to bring out improved software as suggested, perhaps, in red at the bottom of his website?

              Not a facebook user but the group looks interesting and seems to be alive. Applied to join but as an inert user this might fail. Strange comment in the intro: "The underlying theory for TL's discussed in this group is that the fiber stuffing does not move acoustically so the speed of sound is not dramatically reduced." Does anyone know what prompted it?

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              • #8
                There are new and improved versions of the worksheets but I have no plans to make them available. The new worksheets run in MathCad 15 and cannot be saved in a format that uses the free MathCad 8 Explorer program, this severely limits the number of potential DIY users. I do intend to add more documentation to my site and more of my designs.

                With respect to the speed of sound comment, the thing that allowed accurate computer simulations of TLs was the recognition that the speed of sound is not dramatically slowed by the fiber stuffing. This myth dated back to the Bailey and Bradbury papers on TL design. Claims of 50% reduction in the speed of sound can still be found in some discussions on TL design. I wrote the following post in the Facebook group last week on the speed of sound in fiber filled TLs.

                "The speed of sound is a property of the gas itself (oxygen will have a different speed of sound than nitrogen or helium for example) and the thermodynamic process the sound waves undergo. The equation for the speed of sound is shown below.

                c^2 = gamma x Po / density

                where gamma is a ratio of the specific heats which is process dependent and Po is the ambient pressure. For an adiabatic process, which is sound traveling in air, gamma is 1.4 so the speed of sound is approximately 344 m/sec. For an isothermal process, constant temperature expansion and contraction brought about by the fibers absorbing and releasing the heat of compression and expansion, gamma is 1.0 and the speed of sound drops to approximately 290 m/sec. The reduction is about 15%. In reality it is hard to approach isothermal in a fiber filled TL and I limit the reduced speed of sound to correspond with a gamma of 1.2 which yields about 318 m/sec or a 10% reduction.

                The confusion starts when estimating the quarter wave resonant frequency of a TL. For a straight constant area TL open at one end and closed at the other the fundamental frequency can be accurately calculated as follows.

                f = c / (4 x L)

                The problem started when people tried to use this equation to calculate the fundamental frequency for a stuffed tapered TL and compared the value to a measured result. The measured result came out much lower so they assumed that the fiber in the TL slowed the speed of sound by viscous coupling the air to the mass of the fibers effectively increasing the density of the vibrating air column. This is wrong, the reduced frequency is caused by the tapered geometry and the speed of sound is minimally impacted.

                In conclusion, be highly suspicious of any information that claims the speed of sound in a TL is reduced by more than 10%. Anybody who claims a 50% reduction in the speed of sound does not understand how a stuffed TL behaves and neglects the impact of the geometry on the resonant frequency."

                There is still a lot of bad information circulating on the Internet with respect to TL design, fiber stuffing, and the speed of sound.
                Martin

                Quarter Wavelength Loudspeaker Design
                www.quarter-wave.com

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                • #9
                  Martin, I spent some time this weekend reading through some of the articles you wrote “Alignment Tables”, etc. very interesting. I’m a Mechanical Engineer and my son will also be graduating with the same degree this spring. I sent him some pictures of your formulas and he stated it reminded him of linear algebra and differential equations. I also restore antique cars for a hobby. My wife,says for me , “it is not the kill but the thrill of the chase”. So to answer an earlier question, I really want to design them from the ground up. Martin, thank you for the work you have done and replying to this post. I might be able to piece enough together from your available work to build a test enclosure and then go from there.

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                  • #10
                    Originally posted by Brian Steele View Post
                    My workbooks at https://www.diysubwoofers.org/sheets/ and Hornresp can probably do what you want, but you'll have to become familiar with using Hornresp :-).

                    The workbooks allow you to come up with a physical layout using one sample layouts, and then produces a Hornresp import file that allows you to model the results in Hornresp. When looking at the sim using Hornresp's "Loudspeaker Wizard", you can made modifications to the physical layout of the MLTL in the workbook, Export and then press F6 in Hornresp to update the sim.
                    Ok, thanks. I will give it a try.

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                    • #11
                      Originally posted by grubby65 View Post
                      I sent him some pictures of your formulas and he stated it reminded him of linear algebra and differential equations.
                      I am also a mechanical engineer with many years of experience as a structural analyst. It is definitely linear algebra and differential equations along with some AC analog circuit design, 1D finite element theory, and some simple acoustics. Almost all of the fundamentals you need to know can be found in Berenak's Acoustics textbook published in 1954.

                      Martin

                      Quarter Wavelength Loudspeaker Design
                      www.quarter-wave.com

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                      • #12
                        Take a look for some enclosure calculators at

                        http://www.mh-audio.nl

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                        • #13
                          Originally posted by martin View Post
                          There are new and improved versions of the worksheets but I have no plans to make them available. The new worksheets run in MathCad 15 and cannot be saved in a format that uses the free MathCad 8 Explorer program, this severely limits the number of potential DIY users. I do intend to add more documentation to my site and more of my designs.
                          Thanks for clarifying the position. Brian posted that things can be done with Hornresp and so it looks as if design software does exist although how flexible it might be I do not know. For my own design, if it happens, I would use my own software and approach which would require significant additional efforts to put in a form for others to use easily. Given it looks like design software does exist, the demand for your software is currently low and an earlier attempt by myself to gain interest in a group effort for speaker design software failed (though encouraged by mistakes on my part) it looks as if that effort may not be a rewarding use of my hobby time.

                          Originally posted by martin View Post
                          With respect to the speed of sound comment, the thing that allowed accurate computer simulations of TLs was the recognition that the speed of sound is not dramatically slowed by the fiber stuffing. This myth dated back to the Bailey and Bradbury papers on TL design. Claims of 50% reduction in the speed of sound can still be found in some discussions on TL design. [...]
                          Thanks for the clarification. Shortly after posting I spotted that facebook was hiding most of the discussion on the group page which I then opened and read the discussion you quoted. Without the context the statement jarred a bit because this is one of the physical mechanisms that may be significant when two phases are involved in dissipating sound.

                          Originally posted by martin View Post
                          There is still a lot of bad information circulating on the Internet with respect to TL design, fiber stuffing, and the speed of sound.
                          Yes it is strange how audio enthusiasts can pick up technically unreasonable notions and then support them against all comers as if they were a football team. I have recently had similar experiences trying to explain the physics behind cabinet vibration. People seem to get very different things out of their hobby interests.

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                          • #14
                            Originally posted by devnull View Post
                            Take a look for some enclosure calculators at

                            http://www.mh-audio.nl

                            Be very careful with the TL design info given on that site, it is more old school rule of thumb than physics based. If you look at Table 2 on this page

                            http://www.mh-audio.nl/Calculators/Def_TML.html

                            you will find a speed of sound in a fiber filled TL of 123 m/sec which is way too low. There is no accounting for the shape of the TL (tapered, straight, or expanding) in the calculation of a length corresponding to a desired tuning frequency.

                            Designing any form of quarter-wave enclosure using the guidelines, templates, or other software on that site is very hit or miss, you might get lucky but my guess is you will not achieve an optimal result.
                            Martin

                            Quarter Wavelength Loudspeaker Design
                            www.quarter-wave.com

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                            • #15
                              There was also a freeware TL design app by Leonard Audio. I never used it, but some people liked it. The site no longer exists, but you can download the app by using the wayback web site and searching for leonardaudio.co.uk. I believe the last version was 3.6.3.5.
                              "Everything is nothing without a high sound quality." (Sure Electronics)

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