advantages of transmission lines

Discussion in 'Archived Threads 2001-2004' started by eric nyhof, May 5, 2002.

  1. eric nyhof

    eric nyhof Stunt Coordinator

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    What are the advantages of a transmission line as opposed to any other design? I am thinking about ordering the kit281s and possible building the t-line box instead of the ported box, would this be worth it?
     
  2. Ron D Core

    Ron D Core Stunt Coordinator

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    Transmission lines are about as hard to explain, thus making them somewhat confusing to understand. I have come to the conclusion that nobody fully understand the T-line. they say they will after building one that sound good. There are no definite calculations for a T-Line first of all. Most of the design is estimating and guessing. From what I understand is that they offer about flattest, broadest response you can get without going IB. A ported box's response will tend to peak at its tuning frequency and drop off rapidly. A sealed box is flatter and less efficient. The T-Line can be as efficient as the ported AND as flat as the sealed with the right woofer and design. I T-Line will also be very articulate since there is little compression on the woofer. If you have ever heard a properly built T-Line with the right woofer, you'll understand, but it is hard to do. Check out this link it has some good info.
    http://www.t-linespeakers.org/index.html
     
  3. Greg Monfort

    Greg Monfort Supporting Actor

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    Ron, if you'd read Martin King's papers at this site and had used his program to build one you'd know that it's no longer an 'estimating and guessing' type of design. His quantifying pipe resonance to stuffing coefficients WRT T/S takes all the fun out of them.

    GM
     
  4. rodneyH

    rodneyH Supporting Actor

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    ANd for the experts out there, Is the T-line theory similar to B&Ws use of the Nautilus design?? it seems similar to me, but I am NO expert.
     
  5. eric nyhof

    eric nyhof Stunt Coordinator

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    i'm not an expert, but the Nautilus design is different than a T-line. with a t-line the tube has an exit, but with the nautilus it seems to come to a small point after rotating around.
     
  6. eric nyhof

    eric nyhof Stunt Coordinator

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    has anybody built the kit281 t-lines? I think if i decide to get a pair, i'm going to build the t-line boxes and wondered if they are a well designed box.
     
  7. Pete Mazz

    Pete Mazz Supporting Actor

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    I think there is some debate whether two drivers, especially the size of the AV8s, will work well in a TL. As designed, the Kit281TL has a single line to handle both AV8s.
    Of course, DanW designed them![​IMG] So I'd guess they sound great! But I believe even he recommends the ported over the TL.
    Pete
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

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    The size/quantity of the driver(s) has little more to do with it than in a sealed or vented design. The added wrinkle is that where in the line they are affects response.

    The major problem with the TL IMO is it's cross sectional area can get quite large depending on the driver's specs, and of course Fb is determined by its length, so you can wind up with a much larger cab for a given Fb.

    I couldn't find the TL plans, so can't load them into MK's worksheet to get some idea of their response, or does Adire publish it somewhere?

    GM
     
  9. Pete Mazz

    Pete Mazz Supporting Actor

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    Greg
    Adire Kit 281 plans are here.
    The AV8 specs are here.
    With an Sd of almost 36 sq in/driver, the line gets pretty large. I've never had any luck modeling a line with a beginning area(S at 0) of less than 2.
    The 281TL starts with ~34 sq in and tapers to 22.5 sq in.
    Pete
     
  10. Greg Monfort

    Greg Monfort Supporting Actor

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    Thanks for the links! [​IMG] Are you saying you've already used MK's program to sim it?
    GM
     
  11. Adam O

    Adam O Stunt Coordinator

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    What are the characteristics of a t-line that make it more desirable then other designs, 4th, 6th order, ported, sealed etc?

    Also how exactly is this achieved, I understand there are a series of 'chambers' or internal sound 'routers' that control this, but technically speaking how does the air move inside it resulting in the more desirable sounding unit?

    Thanks alot,

    Adam
     
  12. ThomasW

    ThomasW Cinematographer

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    The Nautilus isn't a TL it's a sealed tapered tube.

    Having built dozens of TL's, my suggestion is just say no...Although like most ideas in audio they have a hardcore group of followers.

    They're fun to play with. They tend to be inefficient. We made one in the late 1970's with a single 10" driver that could take the full output from a Phase Linear 700 and wanted more. Changing the stuffing is quite interesting. High density to low, low to high, big slug behind the woofer then varying density. All damping load variations change the performance, as do most changes in damping materials.

    Better to have the box cut in two with a top to bottom diagonal that creates 2 triangular 'lines' instead of having simple rectangular 'lines'. The line can taper, have an inverse taper, or no taper. All effect the performance in different ways.

    My experience is that their response is not flat. And that a 'simple' ported design is usually better

    Others issues are that there are only a limited number of woofers who's T/S parameters are really suited to a TL, and most of those no one wants because of other considerations.

    Adam

    TL's are tuned to a frequency = wavelength. Most of the time the length of the 'line' is 1/4th of that wavelength. Longer lines tend to sound better but can end up quite large. With a TL it's possible to get very low frequency output from a driver, but this is usually at the expense of the top end quality
     
  13. Pete Mazz

    Pete Mazz Supporting Actor

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  14. eric nyhof

    eric nyhof Stunt Coordinator

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    Thanks for the input guys, I might just go with the ported 281's or maybe try to design my own box. I don't have any problems with box designs, but I have no idea about crossovers.
     
  15. ThomasW

    ThomasW Cinematographer

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    eric

    Use one of the Adire designs (ported/sealed). The 281 has some tricks in it to make the 8"s match up with the tweeter. Any changes will cause problems.
     
  16. Michael R Price

    Michael R Price Screenwriter

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    ThomasW,

    Can you explain these 'tricks' that Adire does in the 281?

    Also, the TL is one of Adire's recommended designs, it's in with the others in the plans.
     
  17. Greg Monfort

    Greg Monfort Supporting Actor

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    >I've been playing around with his MathCAD sim for a while. I never broke down and paid for a full version, so I can't save files.

    The 281TL doesn't look like it's line output really helps the FR much. I've never heard it, tho.

    Pete

    ====

    Ok, thanks, no point in me messing with it then.

    ====

    >Thanks for the input guys, I might just go with the ported 281's or maybe try to design my own box. I don't have any problems with box designs, but I have no idea about crossovers.

    ====

    You bet! If DW added any baffle step compensation in the XO then you'll need to keep the baffle width the same, and of course the driver layout needs to be the same.

    GM
     

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