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Want to build a TL subwoofer - driver advice needed
Want to build a TL subwoofer - driver advice needed
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Old 4th March 2018, 07:44 PM   #11
solid7 is offline solid7  United States
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So, with the picture that I posted... How does that fit into the scheme? Assuming one followed the "classic" rules - Low Qts drivers, T/L cross-sectional area proportional to the Vas of the drivers, etc, etc... Could this be used to achieve the goals of a T/L? Or is a T/L rigidly defined by the number, and orientation of the folds in the chamber?

I have all of the means to produce something like that pictured. It's my preferred option, actually.

Please forgive my ignorance. Math and engineering are my education, but the physics of sound and electricity are not.
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Old 4th March 2018, 08:19 PM   #12
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by solid7 View Post
So, with the picture that I posted... How does that fit into the scheme? Assuming one followed the "classic" rules - Low Qts drivers, T/L cross-sectional area proportional to the Vas of the drivers, etc, etc... Could this be used to achieve the goals of a T/L? Or is a T/L rigidly defined by the number, and orientation of the folds in the chamber?

I have all of the means to produce something like that pictured. It's my preferred option, actually.

Please forgive my ignorance. Math and engineering are my education, but the physics of sound and electricity are not.

I can't see the image.

Classical rules don't call for low-Qts drivers. I wouldn't advise anyone to follow the "classical rules" if designing a transmission line enclosure for subwoofer duty anyway.

If I was to define the "modern" approach, I'd say that the design goals of the modern approach (to designing a transmission line subwoofer) would be to produce a design that has the smoothest passband response with largest vent possible (to reduce vent compression effects) and a line taper with suitable driver offset (and possible mass-loading) to move the effect of any higher resonance modes out of the intended passband.
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Old 4th March 2018, 08:29 PM   #13
solid7 is offline solid7  United States
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The image shows a labyrinth. Not straight lines, no square corners.

Perhaps I should just start putting together proposed drivers and geometries.

I was going to build a "test" configuration with my son. The idea is simple: start with a basic box construction of some volume - whether that be based on a sealed, ported, other, recommended volume. Then, the back face of the enclosure would have a series of holes that could be fitted with PVC pipes. I'd start with enough holes to create an opening that was 100-125% of the driver Vas. And the length of the tubes would be the total line length needed, divided by the number of tubes used. Each length would obviously need to be the same, and lengths could be easily added or subtracted, until proper tuning is achieved.

That's my thoughts, anyway...
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Old 4th March 2018, 09:01 PM   #14
Brian Steele is offline Brian Steele  Grenada
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There's no need to do that level of empirical experimenting - Hornresp can do a pretty good job of predicting the response of almost any alignment you can think of. You just to make sure that you model it properly.
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Old 4th March 2018, 09:33 PM   #15
solid7 is offline solid7  United States
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OK, but we still need to get back to my original question, about what constitutes a true T/L. Does the box and tubes or labyrinth methodology satisfy this? Or do I really need an 8' tall phallic structure?

I also don't see a terrible lot of info about the terminus of the T/L, other than the 3 basic shapes: straight, taper flare. What about the designs that I see that are almost horn-like? What does this do? (progressively getting larger, until termination in a bellmouth)

On a side note, the experiment is going to happen, anyway. Kid wants to get into engineering, so it's a test bench. Nothing new to you old vets, but he's pretty excited to see how variations are observed and measured.
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Old 4th March 2018, 10:55 PM   #16
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by solid7 View Post
OK, but we still need to get back to my original question, about what constitutes a true T/L. Does the box and tubes or labyrinth methodology satisfy this? Or do I really need an 8' tall phallic structure?

I also don't see a terrible lot of info about the terminus of the T/L, other than the 3 basic shapes: straight, taper flare. What about the designs that I see that are almost horn-like? What does this do? (progressively getting larger, until termination in a bellmouth)
They are all methods of manipulating 1/4 W resonance. A tapered TL results in a shorter path requirement for the same resonance frequency. An expanding line results in a longer path requirement for the same resonance frequency, but there's a bit of gain as well.


Quote:
Originally Posted by solid7 View Post
On a side note, the experiment is going to happen, anyway. Kid wants to get into engineering, so it's a test bench. Nothing new to you old vets, but he's pretty excited to see how variations are observed and measured.
Good engineering starts with using the right tools to simulate the results of what you're trying to achieve, before committing to an actual build. Sim 20 times, measure twice, cut once .


Have a look here:
He Did The Math

..and here:
The Subwoofer DIY page v1.1 - Transmission Line Systems: Design Notes
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Old 4th March 2018, 11:11 PM   #17
solid7 is offline solid7  United States
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Originally Posted by Brian Steele View Post
Good engineering starts with using the right tools to simulate the results of what you're trying to achieve, before committing to an actual build. Sim 20 times, measure twice, cut once .

Of course, it does... but we can read parameters, charts, and graphs all day long. How does that actually translate into sound? What does a "peak" or "roll-off" mean to the ears? Whats the difference in tuning, to one who has never heard something?

I was an R&D engineer for long enough to appreciate all of the tools in my tool box.
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Old 5th March 2018, 04:44 AM   #18
solid7 is offline solid7  United States
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So, if I'm modeling up a T/L, do I need to make a main chamber equivalent to the volume of a sealed box, with the transmission line distinct from said volume?
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Old 5th March 2018, 10:15 AM   #19
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
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Originally Posted by chris661 View Post
The classic TL was designed to completely absorb the back wave of the driver by funnelling it down a tunnel and...
That is what you would think by the title of Bailey’s article that effectively defined the classic TL, but that is not what he described in the article.

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Old 5th March 2018, 10:23 AM   #20
planet10 is offline planet10  Canada
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Want to build a TL subwoofer - driver advice needed
Quote:
Originally Posted by solid7 View Post
Assuming one followed the "classic" rules
Do not follow Classic rules, they do not work… at least not optimally althou sometimes you wil get lucky.

Quote:
but we still need to get back to my original question, about what constitutes a true T/L.
The work of Augspurger & of King, almost simulataneously relessed in late 1999 changed TL design forever, and as time went along greatly expended the space of possible TL designs.

Read everything here: Quarter Wavelength Loudspeaker Design It will answer a lot of questions. And there are tables that let you design a simple TL.

Quote:
The image shows a labyrinth. Not straight lines, no square corners.
Your image does not show… attach it to a post.

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