A LOT of question about TLs

[mr_push_pull]

Hi people

I'm planning to build a pair of TL's, and since I'm new to this territory, I have a lot of questions. I didn't have the time to thoroughly read Martin King's documentation, and all I want for now is few quick guidelines (I know this isn't the most scientific approach, but lack of time is the issue here).

So, here are my questions:

1. Which are the limits for the tuning frequency of the enclosure? How low can I go with regard to Fs of the driver?
2. Something doesn't make sense to me regarding the "bended" enclosures (the ones with the separating wall inside). And that is, doesn't the abrupt change of cross-section area break the rule that there shouldn't be such sudden changes?
I mean, if you bend an enclosure with an SL that's doesn't equal So, that's not what you get. The TL's with the separating wall resemle better two TL's in series. Could someone shed some light on this issue? I'm pretty confused on this one.
3. I'd like to choose a driver such that the enclosure would be the smallest possible, ideally a straight, "non-bended" one. I would need a few guidelines for choosing the driver.
4. Which one of Martin King's sheets should I use for designing such a TL?

That's it for now. Thanks in advance.

[Mudge]

I would take the time to read as much of Martin's work as you can to be honest.
Different people have different opinions on how TL and TQWT speakers should be designed, and what behaviour is desirable from them.

I personally favour what most people would class as a higher efficiency Linkwitz transform device.
Others would advocate approaches where the system Q is lower in order to lower the F3 point as much as possible. I think this is a good idea for those who prefer greater natural extension at a slight penalty in driver control.
One could also use a driver designed for dipole applications with a very large open line, similar to a finite baffle where the baffle is large enough to ensure that the rear output combines constructively with the front output.

[simon dart]

For what it's worth my advice is: If you don't have much time I shouldn't bother with TL's! They are difficult to design, are a pain in the **** to build properly, take ages to get the stuffing density right blah blah.

There are a few useful design stratagies outlined here:

http://www.t-linespeakers.org/index.html

[Mudge]

Originally posted by simon dart
For what it's worth my advice is: If you don't have much time I shouldn't bother with TL's! They are difficult to design, are a pain in the **** to build properly, take ages to get the stuffing density right blah blah.

There are a few useful design stratagies outlined here:

http://www.t-linespeakers.org/index.html

ditto what Simon said.

Unless you are prepared to invest serious time doing a lot of complicated maths, building a prototype and then modifying it because it doesn't behave quite the way you thought it would, then TLs etc are not worth the bother. Just use a BR or SB design, depending on whether your priorities are output or control.

[Bob Brines]

Or, then, you could simulate your design with MJK's worksheets and fine that the results are nearly spot on. But, I suppose it is more fun to cut-and-try. That way you get to cut more wood.

Regarding folds, a single fold is absolutely transparant in a TL. As long as the fold is properly layed out so that the area does not change in the fold, everything will be alright. More than one fold starts to be unpredicable.

Bob

[mr_push_pull]

I've had that coming.
I know that my approach isn't highly regarded in this king of community, so I deserve that
I tool a look on Martin Kings' documentation (in fact I completely read the "Alignment Tables" pdf), and I have no problem with the scientific approach, in fact I'm an engineer myself, but it's very hard to go through all the details, and finally find out that what you look for isn't even there.
I wouldn't like to be seen as an unwanted intruder in the community.
But I have to tell you that these questions come after a few readings, I've already looked on t-linespeakers.org and read a few design examples.
OK, I'll print down Martin King's papers, and if the questions persist, I'll let you know. Thanks for the patience.

[Mudge]

Originally posted by Bob Brines
Regarding folds, a single fold is absolutely transparant in a TL. As long as the fold is properly layed out so that the area does not change in the fold, everything will be alright. More than one fold starts to be unpredicable.

Bob

Multiple folds are not unpredictable, but a certain level of understanding of the effects of laminar and turbulent flow is required. The goal with a pure TL (which I'm interested in) is a smooth non-resonant restorative force on the driver of a precisely determined value, as in a sealed box.
Fortunately it's not necessary to model the actual flow effects (which is good, because I hate flow mechanics) merely to know the magnitude and compensate for them.

[MJK]

but it's very hard to go through all the details, and finally find out that what you look for isn't even there

What are you looking for?

[mr_push_pull]

My main question is the one concerning the folded TLs.
Maybe I don't understand correcly the notions of So and Sl, but what are those in case of a folded TL? What I do not understand is what happens at the lower end of the separating wall, where you have a sudden change of cross-section area. If the separating wall was parallel to the outside ones (and those would be parallel with each other, in other words a straight TL), it would be clear that it is the case of a folded tube. But with an angle of the separating wall relative to the outside walls plane that doesn't equal zero, I can't imagine how this could resemble a folded tube. I am sure that there is something that I'm getting verry wrong, and I'd like to know what is that.
I hope I'm not too annoying, and I am sure that the answer for that is found in one of the pdf's, I am sorry for not giving it a proper reading, I will correct that in the near future.

[Bob Brines]

Mr_Push_Pull,

You are making way too big a deal out of the bend in a pipe. the short length of the pipe that actually contains the are discontinuity is, for practical purposes, irrelavant. The plot I supplied is a conventional TL withan 8:1 taper ratio and a 180 degree fold ~2/3 the length of the pipe. The plot shows with and without corner reflectors, which significantly change the pipe area at the fold. No difference. (Black=No Reflector Blue=Reflectors Green=Fiberglas making a smooth bend Red=Unstuffed pipe)



Mudge is right, you can go to engineering tables and caclulate the flow reduction in the bend. Again, no practical change in the port SPL for a single fold.

Don't worry about it.

Bob