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.
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.
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.
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.
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
There are a few useful design stratagies outlined here:
http://www.t-linespeakers.org/index.html
ditto what Simon said.simon dart 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.
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
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
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.
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.
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.Bob Brines said:
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.
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.
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.
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
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)
An externally hosted image should be here but it was not working when we last tested it.
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
If I remember correctly then the following should help.
The enclosure shown in the TL Application note is a folded straight TL, my Focal two-way design. This enclosure is modeled in the "TL Sections" worksheet. Use this worksheet as a sample problem to model a fold in your design.
I agree with Bob's post. For a single fold, the first standing wave will not even know it exists. Higher in frequency it may be important but hopefully the fiber damps any artifacts. I have verified this a number of times by using ANSYS to calculate the quarter wavelength resonant frequencies and correlating against an unstuffed MathCad TL simulation.
While this method for modeling a fold is probably not absolutely technically correct from a fluid flow perspective, I believe that the error introduced is well below the level of errors introduced by other assumptions made in the formulation of the MathCad worksheets or many of the lumped parameter computer codes available for closed and ported boxes. Remember that the MathCad worksheets are a tool for making intelligent design decisions and not a prediction of how a speaker system will actually sound.
Hope that helps,
The enclosure shown in the TL Application note is a folded straight TL, my Focal two-way design. This enclosure is modeled in the "TL Sections" worksheet. Use this worksheet as a sample problem to model a fold in your design.
I agree with Bob's post. For a single fold, the first standing wave will not even know it exists. Higher in frequency it may be important but hopefully the fiber damps any artifacts. I have verified this a number of times by using ANSYS to calculate the quarter wavelength resonant frequencies and correlating against an unstuffed MathCad TL simulation.
While this method for modeling a fold is probably not absolutely technically correct from a fluid flow perspective, I believe that the error introduced is well below the level of errors introduced by other assumptions made in the formulation of the MathCad worksheets or many of the lumped parameter computer codes available for closed and ported boxes. Remember that the MathCad worksheets are a tool for making intelligent design decisions and not a prediction of how a speaker system will actually sound.
Hope that helps,
mr_push_pull said:
A lot of those questions are answered on Bob B's site
http://geocities.com/rbrines1/
and to a lesser extent on mine...
dave
Related to a transmission line, has anyone ever tried seperating two identical drivers, operating in phase, by a full wavelength line?
The theory works quite well, when the two drivers are spaced precisely one wavelength apart, the rear waves from the drivers precisely cancel out. Obviously the practicality sucks, since the line has to be a full wavelength.
The theory works quite well, when the two drivers are spaced precisely one wavelength apart, the rear waves from the drivers precisely cancel out. Obviously the practicality sucks, since the line has to be a full wavelength.
Yes that helped, thank you.
The question that remains is: is there any way to derive the dimensions of a folded tapered TL from a non-folded one?
Because it seems more of a random process otherwise.
Thank you again for the clarifications, they helped a lot.
The question that remains is: is there any way to derive the dimensions of a folded tapered TL from a non-folded one?
Because it seems more of a random process otherwise.
Thank you again for the clarifications, they helped a lot.
That makes sense, but could you give more details please? For instance, do you have a rule of thumb for setting the intermediate cross-sectional areas for the folded line? Hey, I think I'll need to make some drawings to clarify what I'm trying to say.
>1. Which are the limits for the tuning frequency of the enclosure? How low can I go with regard to Fs of the driver?
====
Except for compression loaded horns, 0.707*Fs is the practical limit.
====
>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?
====
As BB's plot shows, it's mostly a function of how much BW you want to 'pass' through the bend unattenuated. Typically, you want to damp down all the BW > the driver's effective mass corner, i.e. (Fs*2)/Qes.
====
>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.
====
I see this has been covered fairly well already, so I'll just add that as frequency falls, acoustic energy increases (1/f), so looking at the various cross sectional area (CSA) discontinuities of one or more bends, you'll see that the magnitude of how much variance a WL is compressed between the various CSAs is negligible WRT its size until you're up above the driver's mass corner in the larger CSA cabs.
IOW, until the CSA is >than the max frequency we want to 'round the bend', it's a non-issue. To determine the CSA's compression passband: ~4316.28in/((CSA)^0.5*2). Or if you want to calculate the max CSA based on the mass corner, then: ~((4316.28/mcf)/2)^2. FWIW, to ensure good attenuation, I use the max CSA value*0.707 and let the stuffing attenuate reflections back to the driver/S0.
Since we normally want the BW above this point attenuated, why not let the cab do it in lieu of increased stuffing, which may shift the driver's mass corner, causing a dip in the FR?
====
>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.
====
Well, a TL is ~a 1/4W long of whatever Fp you choose, and Fp should ideally = Fs, so how much LF BW are you willing to give up for a short line? If you're willing to accept a high compression ratio reverse taper or use a vent (ML-TL), then it can be much shorter for a given Fp.
WRT CSA, the taller the pipe, the smaller the CSA, or the smaller the Vas and Qts, etc.. They follow TS theory, so you can use a regular vented box calculator to get the desired Vb/Fb, then it's just a matter of picking an acceptable tradeoff between height/CSA and plugging the numbers into the MLTQWT worksheet and try different taper ratios or vent lengths, driver positions, and stuffing density until you get the desired FR.
If you can't get an acceptable result, then obviously you need to either rethink the alignment.
====
>4. Which one of Martin King's sheets should I use for designing such a TL?
====
Depends on your performance/size goals, and since I suck at mind reading, you'll have to tell me. 😉
====
>I personally favour what most people would class as a higher efficiency Linkwitz transform device.
====
Me too, though I think most folks would classify such a device as a compression loaded horn.
====
>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.
====
Lowering or raising sysQ referenced to 0.707 (max flat) raises F3 and lowering sysQ increases driver control due to increased damping.
====
>They are difficult to design, are a pain in the **** to build properly, take ages to get the stuffing density right blah blah.
>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.
====
Before T/S's, Augsperger's, MJK's, and various computer hardware/software designer's contributions, the DIYer was pretty much 'flying blind' with his/her's slide rule if he/she didn't have a good grounding in electro-mechanical engineering and the test equipment to measure BL, Cms, Fs, etc........
With a computer, a vented box program, Mathcad, MJK's TL worksheet, and published specs though, at least as good, and probably better, performing designs can be whipped up in at most a matter of hours in today's hi-tech world. Or for TL you can fall back on MJK's classic design tables and be done in ~15min..
====
>That makes sense, but could you give more details please? For instance, do you have a rule of thumb for setting the intermediate cross-sectional areas for the folded line? Hey, I think I'll need to make some drawings to clarify what I'm trying to say.
====
Per mine and other's comments, BB's dwgs. of folded lines at his website are 'close enough' WRT accuracy, i.e. constant radius. If you're trying to visualize where, and at what angle to add corner deflectors to pass a given BW, then maybe this will help you more than who I addressed it to: http://f18.parsimony.net/forum31999/messages/65967.htm
GM
====
Except for compression loaded horns, 0.707*Fs is the practical limit.
====
>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?
====
As BB's plot shows, it's mostly a function of how much BW you want to 'pass' through the bend unattenuated. Typically, you want to damp down all the BW > the driver's effective mass corner, i.e. (Fs*2)/Qes.
====
>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.
====
I see this has been covered fairly well already, so I'll just add that as frequency falls, acoustic energy increases (1/f), so looking at the various cross sectional area (CSA) discontinuities of one or more bends, you'll see that the magnitude of how much variance a WL is compressed between the various CSAs is negligible WRT its size until you're up above the driver's mass corner in the larger CSA cabs.
IOW, until the CSA is >than the max frequency we want to 'round the bend', it's a non-issue. To determine the CSA's compression passband: ~4316.28in/((CSA)^0.5*2). Or if you want to calculate the max CSA based on the mass corner, then: ~((4316.28/mcf)/2)^2. FWIW, to ensure good attenuation, I use the max CSA value*0.707 and let the stuffing attenuate reflections back to the driver/S0.
Since we normally want the BW above this point attenuated, why not let the cab do it in lieu of increased stuffing, which may shift the driver's mass corner, causing a dip in the FR?
====
>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.
====
Well, a TL is ~a 1/4W long of whatever Fp you choose, and Fp should ideally = Fs, so how much LF BW are you willing to give up for a short line? If you're willing to accept a high compression ratio reverse taper or use a vent (ML-TL), then it can be much shorter for a given Fp.
WRT CSA, the taller the pipe, the smaller the CSA, or the smaller the Vas and Qts, etc.. They follow TS theory, so you can use a regular vented box calculator to get the desired Vb/Fb, then it's just a matter of picking an acceptable tradeoff between height/CSA and plugging the numbers into the MLTQWT worksheet and try different taper ratios or vent lengths, driver positions, and stuffing density until you get the desired FR.
If you can't get an acceptable result, then obviously you need to either rethink the alignment.
====
>4. Which one of Martin King's sheets should I use for designing such a TL?
====
Depends on your performance/size goals, and since I suck at mind reading, you'll have to tell me. 😉
====
>I personally favour what most people would class as a higher efficiency Linkwitz transform device.
====
Me too, though I think most folks would classify such a device as a compression loaded horn.
====
>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.
====
Lowering or raising sysQ referenced to 0.707 (max flat) raises F3 and lowering sysQ increases driver control due to increased damping.
====
>They are difficult to design, are a pain in the **** to build properly, take ages to get the stuffing density right blah blah.
>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.
====
Before T/S's, Augsperger's, MJK's, and various computer hardware/software designer's contributions, the DIYer was pretty much 'flying blind' with his/her's slide rule if he/she didn't have a good grounding in electro-mechanical engineering and the test equipment to measure BL, Cms, Fs, etc........
With a computer, a vented box program, Mathcad, MJK's TL worksheet, and published specs though, at least as good, and probably better, performing designs can be whipped up in at most a matter of hours in today's hi-tech world. Or for TL you can fall back on MJK's classic design tables and be done in ~15min..
====
>That makes sense, but could you give more details please? For instance, do you have a rule of thumb for setting the intermediate cross-sectional areas for the folded line? Hey, I think I'll need to make some drawings to clarify what I'm trying to say.
====
Per mine and other's comments, BB's dwgs. of folded lines at his website are 'close enough' WRT accuracy, i.e. constant radius. If you're trying to visualize where, and at what angle to add corner deflectors to pass a given BW, then maybe this will help you more than who I addressed it to: http://f18.parsimony.net/forum31999/messages/65967.htm
GM
This is as exhaustive as it gets.
Well, I'll seriously think if building a TL is worth the pain. What got me started was finding about MJK's revolutionary (I believe it is) work. And when I found that usual box speaker design software doesn't even take into consideration the quarter wave phenomenon, I said that I have to seriously look into TLs. And the idea of good bass even from a mid-range is surely appealing.
An option may be using MJK's sheets to design a standard ported enclosure. But, doesn't this get me where I started? I mean, I haven't seen a software design program (and I'm talking the accessible stuff here, not exotic things like LEAP or whatever) that takes into account so many parameters (for instance, stuffing density). Most of these programs have at most a stuffing quantity setting (none, small, medium, etc). So in the end I still have to adjust the stuffing density/position and all that, to get a good sounding loudspeaker.
The only advantage would be a simpler enclosure.
Bottom line, there's a trade-off between sound quality and difficulty of design/construction.
PS: I can't believe I wrote "bended" instead of "bent"; I'll remember in the future not to post anything on a forum when I'm tired
Well, I'll seriously think if building a TL is worth the pain. What got me started was finding about MJK's revolutionary (I believe it is) work. And when I found that usual box speaker design software doesn't even take into consideration the quarter wave phenomenon, I said that I have to seriously look into TLs. And the idea of good bass even from a mid-range is surely appealing.
An option may be using MJK's sheets to design a standard ported enclosure. But, doesn't this get me where I started? I mean, I haven't seen a software design program (and I'm talking the accessible stuff here, not exotic things like LEAP or whatever) that takes into account so many parameters (for instance, stuffing density). Most of these programs have at most a stuffing quantity setting (none, small, medium, etc). So in the end I still have to adjust the stuffing density/position and all that, to get a good sounding loudspeaker.
The only advantage would be a simpler enclosure.
Bottom line, there's a trade-off between sound quality and difficulty of design/construction.
PS: I can't believe I wrote "bended" instead of "bent"; I'll remember in the future not to post anything on a forum when I'm tired
answer to question 4 at the beginning
Martin's "ML TL" worksheet seems to be the easiest to design a half TL, half BR enclosure. It is this type of enclosure http://www.quarter-wave.com/Project03/Project03.html and rarely requires a fold from what I can see.
I was going to build one, but then just went with sealed do to the size and i like sealed enclosures a lot, but they have no bass.
Martin's "ML TL" worksheet seems to be the easiest to design a half TL, half BR enclosure. It is this type of enclosure http://www.quarter-wave.com/Project03/Project03.html and rarely requires a fold from what I can see.
I was going to build one, but then just went with sealed do to the size and i like sealed enclosures a lot, but they have no bass.
Mr Push Pull,
I am not sure what your experience is using MathCad. But if you are willing to try the program I think you will find that the learning curve is not that long, it is really fairly easy if you start simple and work towards the more complex worksheets. I personally would rather learn and adjust the paper design before I build something. If you can get past the initial MathCad learning, I think that you will find all of the worksheets easy to use. At that point there is no difference in designing a TL, a horn, or a standard BR or closed box. Bottom line, using the MathCad worksheets may look like more work but it is really not that hard.
As for building a box, I don't see any great difference building a TL, TQWT, BR, or sealed box. It is just geometry and maybe an extra divider or brace. Woodworking is not my strongest skill and I have done it without screwing up too bad. Again, not that much more difficult to build a TL.
So the real question is how much extra learning are you willing to take on to build something a little more interesting and challenging. Simple closed or ported two-way ..... ho-hum ho-hum. Quarter wave design ..... eye catcher and conversation piece. I think each design has the same excellent chance of success if you use the MathCad worksheets.
I am not sure what your experience is using MathCad. But if you are willing to try the program I think you will find that the learning curve is not that long, it is really fairly easy if you start simple and work towards the more complex worksheets. I personally would rather learn and adjust the paper design before I build something. If you can get past the initial MathCad learning, I think that you will find all of the worksheets easy to use. At that point there is no difference in designing a TL, a horn, or a standard BR or closed box. Bottom line, using the MathCad worksheets may look like more work but it is really not that hard.
As for building a box, I don't see any great difference building a TL, TQWT, BR, or sealed box. It is just geometry and maybe an extra divider or brace. Woodworking is not my strongest skill and I have done it without screwing up too bad. Again, not that much more difficult to build a TL.
So the real question is how much extra learning are you willing to take on to build something a little more interesting and challenging. Simple closed or ported two-way ..... ho-hum ho-hum. Quarter wave design ..... eye catcher and conversation piece. I think each design has the same excellent chance of success if you use the MathCad worksheets.
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