Want to build a TL subwoofer - driver advice needed

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I have gotten the DIY bug again, and really want to do a transmission line subwoofer. I don't need to blow the roof off of the house. Just something that sounds really nice with my soon-to-be built Zaph ZRT mains.

I was thinking to start off with a 10" woofer, and maybe add a second one later, if I like the result. I've been away from the home audio thing for a few years, so I'm not so current on driver selection.

I'd really like to find a driver in the $500 or less range that suits a TL well. Obviously, I want the best sound possible, but I'm a sucker for a good value proposition. (meaning I don't mind cheap drivers if they're awesome)

Thanks in advance
 
I'd start the search by looking for a driver with a Qts between 0.35~0.40 and an Fs around the cutoff frequency I'm looking for, e.g. 20 Hz ~ 30 Hz.

With a budget of $500, that opens a whole lot of possibilities. Were I ever tempted to spend that much on a 10" driver, I'd probably look at the Morel TiCW 1058Ft - Morel TiCW 1058Ft Titanium Series 10" Subwoofer 8 Ohm

I'd probably opt for something cheaper though, like the Dayton Audio RSS265HO:

Dayton Audio RSS265HO-4 10" Reference HO Subwoofer 4 Ohm
 
I have always been a fan of the Dayton drivers, but should I be worried that the F3 of the Dayton is 39 Hz, vs 29 Hz of the Morel? Dayton has the Morel beat on xmax, but I realize this isn't going to be the ultimate factor...

Ignore the F3 given on the page - that's dependent on the vented alignment given on the page, and you're not going to be using that :)
 
I've seen some advice to keep the Qts low, and some say that higher Qts drivers are preferred.

Maybe this would be a better question: If I were to want to build a T/L speaker, what is probably the most definitive resource for a DIY'er today? There used to be several box modeling softwares out there. Can't seem to find much, anymore. I don't see tons of discussions, anymore.

I'd also really like some clarification on what constitutes a T/L, vs just a long vented port? Or with modern manufacturing methods, there are more and more "labyrinth" designs. Is that a true T/L?

main-qimg-b29810db2c85fa9b3855833b7517b690.webp
 
The definition of a transmission line speaker has become quite diluted in recent years. The classic TL was designed to completely absorb the back wave of the driver by funnelling it down a tunnel and increasing the stuffing density until all the sound was absorbed. The result would be something similar to the bass response you get with an infinite baffle (NB - not the same as a sealed box).

These days, most TLs are some variant on a quarter-wave resonator, which often ends up quite similar to a ported box in terms of response, output and cabinet size.

IMO, for ultimate sound quality at home, sealed boxes are the way to go, unless you want to go below 25Hz with real power. In that case, tuned enclosures are the way to do it unless you've got the budget for a lot of cone area and power.

Chris
 
The definition of a transmission line speaker has become quite diluted in recent years. The classic TL was designed to completely absorb the back wave of the driver by funnelling it down a tunnel and increasing the stuffing density until all the sound was absorbed. The result would be something similar to the bass response you get with an infinite baffle (NB - not the same as a sealed box).

Yup, that's the polite way of putting classical TL design. The less-polite way was that the lines probably end up getting very stuffed to reduce the awful resonances caused by using too-big enclosures due to the use of inaccurate "design rules" used for building the things. Stuffing significantly reduced the response from the vent, the end result being a response similar to what you'd get with the same driver in an infinite baffle arrangement. No wonder higher-Q drivers were liked for this type of build.
 
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.
 
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.
 
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...
 
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.
 
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.


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
 
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. :)
 
frugal-phile™
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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.

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.

The image shows a labyrinth. Not straight lines, no square corners.

Your image does not show… attach it to a post.

dave
 
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