The first picture at the first page offers an horrendous view, being 1/4 th of
back wave emitted from the speaker reflected by the near corner .
This , only by viewing from the 'outside' . So the phisics of the TL must
also consider what happens in the vicinity of the cone itself .
Never heard of flared corners around driver's hole , to minimize the very early reflections ?
So , this goes together with the low Vas superimposed , that leads to geometrical links . So far , a cylindrical enclosure is the worst for preventing more backwave redundant reflections, so the pipe concept has to evolve.
I do like the idea of a double line . The best would be an infinite ...line
back wave emitted from the speaker reflected by the near corner .
This , only by viewing from the 'outside' . So the phisics of the TL must
also consider what happens in the vicinity of the cone itself .
Never heard of flared corners around driver's hole , to minimize the very early reflections ?
So , this goes together with the low Vas superimposed , that leads to geometrical links . So far , a cylindrical enclosure is the worst for preventing more backwave redundant reflections, so the pipe concept has to evolve.
I do like the idea of a double line . The best would be an infinite ...line
picowallspeaker,
an alternative to a simple Tee connection with the reflective problems you are taking about would be to use a Y connector followed by a couple of 45degree connections if you wanted a vertically designed main pipe sections.There are many ways to do what you are talking about. Lining the inside of the tube with absorbent materials is another option. You could even look at a stuffed terminated tube idea if you wanted to simulate an infinite baffle. How about simple traps by varying the pipe diameter and creating specific resonator chambers. There are many ways to skin this cat.
Steven
an alternative to a simple Tee connection with the reflective problems you are taking about would be to use a Y connector followed by a couple of 45degree connections if you wanted a vertically designed main pipe sections.There are many ways to do what you are talking about. Lining the inside of the tube with absorbent materials is another option. You could even look at a stuffed terminated tube idea if you wanted to simulate an infinite baffle. How about simple traps by varying the pipe diameter and creating specific resonator chambers. There are many ways to skin this cat.
Steven
I agree kindhornman. I found in my el cheapo Bo-zooka experiment, that I could actually use very little stuffing in the pipe to almost remove the 'pipe sound' while maintaining as much gain in the bass as possible.
In the end I had a loose plug of BAF in the terminus, and a 20mm x 20mm x 750mm strip of PU foam running through the centre of the tube.
I used a long knitting needle to 'thread' the foam along a piece of wool, that was pulled taught. This held the foam centrally, allowing a 'ring' of unimpeded air flow through the rest of the tube.
Worked far better than I imagined it would. Good strong bass (for a 3" driver) from the vented end, and yet a great reduction in the pipe harmonics, AND I believe it was especially good at sorting out the radial standing wave problems that a round tube can show.
I will most definitely be using that approach again!
In the end I had a loose plug of BAF in the terminus, and a 20mm x 20mm x 750mm strip of PU foam running through the centre of the tube.
I used a long knitting needle to 'thread' the foam along a piece of wool, that was pulled taught. This held the foam centrally, allowing a 'ring' of unimpeded air flow through the rest of the tube.
Worked far better than I imagined it would. Good strong bass (for a 3" driver) from the vented end, and yet a great reduction in the pipe harmonics, AND I believe it was especially good at sorting out the radial standing wave problems that a round tube can show.
I will most definitely be using that approach again!
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mondogenerator,
That is an interesting idea of the central absorbing strip instead of lining the wall. I wonder what a spiral winding would do?
That is an interesting idea of the central absorbing strip instead of lining the wall. I wonder what a spiral winding would do?
Using foam inside the pipe reminds me that I used it in some points , to keep
the volumes equal (-ly tapering). Indeed , the forces involved as also internal volumes are proportional to driver's area .
A spin-off from that project ( tapered tube ) for a smaller speaker , now I use an elliptical from a Tv , uses foam cut to fit in the same manner .
Drivers are kept at 1/5 from the start of the TL .
the volumes equal (-ly tapering). Indeed , the forces involved as also internal volumes are proportional to driver's area .
A spin-off from that project ( tapered tube ) for a smaller speaker , now I use an elliptical from a Tv , uses foam cut to fit in the same manner .
Drivers are kept at 1/5 from the start of the TL .
picowallspeaker,
1/5 is a strange tuning, how and why did you come up with that instead of a standard 1/4 wave length? Or are you just shifting the cutoff up a set point in your line?
1/5 is a strange tuning, how and why did you come up with that instead of a standard 1/4 wave length? Or are you just shifting the cutoff up a set point in your line?
It's not a tuning per se since offsetting the driver doesn't change the pipe's 1/4 WL fundamental tuning, just alters its harmonic structure to achieve a different combined response.
GM
Gm,
I had to go look up all the different types of transmission lines as I wasn't familiar with the abbreviations. I read about the few different tuning arrangements and I see what he is doing by the placement offset from the end of the line. It is still a terminate line or open line with the same internal volume but with tapering cross sections. I can see all the different permutations and how they are working. Thanks.
I had to go look up all the different types of transmission lines as I wasn't familiar with the abbreviations. I read about the few different tuning arrangements and I see what he is doing by the placement offset from the end of the line. It is still a terminate line or open line with the same internal volume but with tapering cross sections. I can see all the different permutations and how they are working. Thanks.
from what i understand, and offset at between 2/3rds and 4/5ths will help suppress the 3rd and 5th harmonics. MJK theory goes somethat further and models it.
The aim with the foam in the centre of the tube was to cover the anti nodes. The strip is central radially, and about 1/3rd the diameter. Thus it should suppress the f3 and f5 radial harmonics, and the axial 'length' as a result is also distributed over 2/3rds the pipe length, covering the pipe modes. The small wad of BAF just seemed to tame the bass response
Id love to try some good felt instead of foam and see the effects, or hear
The aim with the foam in the centre of the tube was to cover the anti nodes. The strip is central radially, and about 1/3rd the diameter. Thus it should suppress the f3 and f5 radial harmonics, and the axial 'length' as a result is also distributed over 2/3rds the pipe length, covering the pipe modes. The small wad of BAF just seemed to tame the bass response
Id love to try some good felt instead of foam and see the effects, or hear
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Hi,
No I'm not. No way am I going to tell a student how to do it or more
than once allude to how they may be going wrong. They can come
here and get answers to good questions, but that is about it.
rgds, sreten.
sreten,
I wasn't trying to tell him what to do. It was really his idea, I was only giving out ideas. He can do whatever he wants to do. It was just a suggestion instead of having to make a wooden enclosure. He could still do that. He is the only one to actually make that decision, what to do and how to present it. We can only give advise or suggestion, this is his work to do. If you noticed I never told him any one speaker to use or gave any actual dimensions for him to use, he needs to do his own work and discover what the math and physics teach him.
I wasn't trying to tell him what to do. It was really his idea, I was only giving out ideas. He can do whatever he wants to do. It was just a suggestion instead of having to make a wooden enclosure. He could still do that. He is the only one to actually make that decision, what to do and how to present it. We can only give advise or suggestion, this is his work to do. If you noticed I never told him any one speaker to use or gave any actual dimensions for him to use, he needs to do his own work and discover what the math and physics teach him.
guys, let's agree to agree...
...to helping Rullknufs, but not do his work for him.
Rullknufs: At this stage, just adopt a speaker construction method, and a fullrange or co-axial driver (with a cap to roll off the tweeter if need be). Then look at it's parameters, and build something. The quicker the better. That's why I keep plugging "toobs" etc--very quick build, and if not glued (if PCV used) then easy to modify. Once satisfied, then glue up if need be, and finish them (particularly if you are proud of them).The more time you spend on the project (the write-up) the more likely you will complete it.
There are many inexpensive drivers available in Europe. As I am not familiar with them, others will have to offer some comments, but Monacor (?), Mapins, etc., may be a place to look. Don't worry if the driver is not ideal for a TL, just get something. Less than ideal performance can be explained in the write-up as a budget consideration regarding a driver choice. If you choose free materials for the build (or very limited expenditure) then there must be some budget for drivers. Even non-modified EL70s or similar should be possible on a very restricted budget. Set some sort of budget for the build initially as well. Ask your folks for some help as this will be a final project and (I am assuming) would constitute a significant portion of your final grade in school. Is £75 too much for a budget? What about £50? Start collecting free materials today as well.
Understanding the requirements for the write up is probably the toughest part. What level of write-up are you expected to provide? Something suitable for publication in a scientific journal? Citing your references will take a long time, and explaining the mathematics/physics of the project will also take a significant amount of time and space. Don't leave the write-up to the end. I'd start a journal today if possible to begin the documentation process.
...to helping Rullknufs, but not do his work for him.
Rullknufs: At this stage, just adopt a speaker construction method, and a fullrange or co-axial driver (with a cap to roll off the tweeter if need be). Then look at it's parameters, and build something. The quicker the better. That's why I keep plugging "toobs" etc--very quick build, and if not glued (if PCV used) then easy to modify. Once satisfied, then glue up if need be, and finish them (particularly if you are proud of them).The more time you spend on the project (the write-up) the more likely you will complete it.
There are many inexpensive drivers available in Europe. As I am not familiar with them, others will have to offer some comments, but Monacor (?), Mapins, etc., may be a place to look. Don't worry if the driver is not ideal for a TL, just get something. Less than ideal performance can be explained in the write-up as a budget consideration regarding a driver choice. If you choose free materials for the build (or very limited expenditure) then there must be some budget for drivers. Even non-modified EL70s or similar should be possible on a very restricted budget. Set some sort of budget for the build initially as well. Ask your folks for some help as this will be a final project and (I am assuming) would constitute a significant portion of your final grade in school. Is £75 too much for a budget? What about £50? Start collecting free materials today as well.
Understanding the requirements for the write up is probably the toughest part. What level of write-up are you expected to provide? Something suitable for publication in a scientific journal? Citing your references will take a long time, and explaining the mathematics/physics of the project will also take a significant amount of time and space. Don't leave the write-up to the end. I'd start a journal today if possible to begin the documentation process.
As for the budget I'm willing to spend maximum $300 for the whole project, including drivers, material and other stuff needed.
This is no final project to sum up my three years in high school. This is just one course among all the others, but just as important as the others.
The level is not that high. To give some examples of what I saw at the exhibition last year (where I will participate this year)... One guy had written a strength training guide, another guy had constructed a vise in metal, two guys had biked through sweden and documenting their trip. Two girls had organized a consert to raise funds for some forest project in africa. The level is not "university level", bear in mind that I'm only 17 and still in high-school so the level isn't that very high. I guess that if I keep it on a "standard" level by our (DIY-ers) means it will be on a high enough level for people that are not into DIY.
This is no final project to sum up my three years in high school. This is just one course among all the others, but just as important as the others.
The level is not that high. To give some examples of what I saw at the exhibition last year (where I will participate this year)... One guy had written a strength training guide, another guy had constructed a vise in metal, two guys had biked through sweden and documenting their trip. Two girls had organized a consert to raise funds for some forest project in africa. The level is not "university level", bear in mind that I'm only 17 and still in high-school so the level isn't that very high. I guess that if I keep it on a "standard" level by our (DIY-ers) means it will be on a high enough level for people that are not into DIY.
no Dummies here
I just wanted to know what level of write-up and suggest limited help might be the correct thing to do so that Rullknufs actually gains the experience of the project.
Rullknufs:Perhaps adopt a level of write-up that would be suitable for a Grade 12 science class (experimental based such as Physics or Chemistry lab write-ups), but a little less formal. You can always add an introduction explaining the complete goals of the project (it's not just an experiment), and your interest in the subject. If any measurements or calculations are done remember to include a very basic error analysis section. Also write up a meaningful conclusion using the same style as your project introduction.
It is important to keep whatever discussion level appropriate, as well as the theory and mathematics. It sounds like you have a grasp on that.
I say this as I used to mark exams and assignments in university Physics and Astronomy, and many would not include some sort of conclusion regarding calculations or any error analysis (even the most basic). I was generous in my marking but if any complained to the Proff, they usually got fully docked....
'Acoustical TL Tutorial for Dummies', eh?
I just wanted to know what level of write-up and suggest limited help might be the correct thing to do so that Rullknufs actually gains the experience of the project.
Rullknufs:Perhaps adopt a level of write-up that would be suitable for a Grade 12 science class (experimental based such as Physics or Chemistry lab write-ups), but a little less formal. You can always add an introduction explaining the complete goals of the project (it's not just an experiment), and your interest in the subject. If any measurements or calculations are done remember to include a very basic error analysis section. Also write up a meaningful conclusion using the same style as your project introduction.
It is important to keep whatever discussion level appropriate, as well as the theory and mathematics. It sounds like you have a grasp on that.
I say this as I used to mark exams and assignments in university Physics and Astronomy, and many would not include some sort of conclusion regarding calculations or any error analysis (even the most basic). I was generous in my marking but if any complained to the Proff, they usually got fully docked....
Nanook,
I think that you are giving excellent advice here to Rullknufs. I didn't realize that this was a high school project, I erroneously thought that it was a college level project. Part of the goal may be to simply present the mathematics for a high school audience. As you pointed out all research papers follow a similar structure at any levels of education, just the level of detail, length and grammatic structure will change with level. So the question will be how can we help simplify the basic applications of TL design so he can move forward.
Steven
I think that you are giving excellent advice here to Rullknufs. I didn't realize that this was a high school project, I erroneously thought that it was a college level project. Part of the goal may be to simply present the mathematics for a high school audience. As you pointed out all research papers follow a similar structure at any levels of education, just the level of detail, length and grammatic structure will change with level. So the question will be how can we help simplify the basic applications of TL design so he can move forward.
Steven
How we can help.
I think that Rullknufs has some understanding, but the connection between the Helmholtz equation and a TL may need a little explanation (nothing too in-depth). Once that connection is made, then the math should be reasonably easy using the equations and the derivations that he has been exposed to. If measurements comparing the theoretical output and the actual output can be made then that would be enough to prove his understanding of the concepts. Tapering a TL (either as a TL or horn) introduces a lot more mathematics and a lot more theory. I'm not sure I could describe it all correctly myself without spending a significant amount of time learning and experimenting.
One area where he may need or ask for assistance is for someone to model the performance of the designed loudspeaker and then do measurements to consolidate the measurements and the theoretical outputs. To do a frequency sweep doesn't require a lot of equipment...I'd suggest the school may already have all the equipment needed.
I think that Rullknufs has some understanding, but the connection between the Helmholtz equation and a TL may need a little explanation (nothing too in-depth). Once that connection is made, then the math should be reasonably easy using the equations and the derivations that he has been exposed to. If measurements comparing the theoretical output and the actual output can be made then that would be enough to prove his understanding of the concepts. Tapering a TL (either as a TL or horn) introduces a lot more mathematics and a lot more theory. I'm not sure I could describe it all correctly myself without spending a significant amount of time learning and experimenting.
One area where he may need or ask for assistance is for someone to model the performance of the designed loudspeaker and then do measurements to consolidate the measurements and the theoretical outputs. To do a frequency sweep doesn't require a lot of equipment...I'd suggest the school may already have all the equipment needed.
Sounds very interesting, indeed. We have only started studying waves but I looked a few pages forward and found some stuff about standing waves in tubes. I guess we'll go through that this week in physics class.
Simulating a response and then measuring and compare the two would be a fun project. I don't think the school has any measuring microphones (we do have mics for singing and instruments though) but they do have some kind of oscilloscopes and other electrics equipment. I have a digital radioshack SPL-meter the might be usable. Otherwise I could just build a Gainhpile measuring mic, it's not that expensive.
So... Building some kind of speakers with a TL or similar. Model the performance and then measure it and see if it corresponds with eachother (correct terms??). And then have the actual speakers playing on the exhibition. Have papers where I have gone a bit in detail in how the TL works, some models and measurements maybe.
Edit: Seems like most things are clear now. I think I'll be able to do most of the paperwork myself, maybe asking you for directions some times since I think my school books wont go that much in detail how a TL works. But your task is to find suitable drivers and cabinet options because I have no idea at all what to look for.
Simulating a response and then measuring and compare the two would be a fun project. I don't think the school has any measuring microphones (we do have mics for singing and instruments though) but they do have some kind of oscilloscopes and other electrics equipment. I have a digital radioshack SPL-meter the might be usable. Otherwise I could just build a Gainhpile measuring mic, it's not that expensive.
So... Building some kind of speakers with a TL or similar. Model the performance and then measure it and see if it corresponds with eachother (correct terms??). And then have the actual speakers playing on the exhibition. Have papers where I have gone a bit in detail in how the TL works, some models and measurements maybe.
Edit: Seems like most things are clear now. I think I'll be able to do most of the paperwork myself, maybe asking you for directions some times since I think my school books wont go that much in detail how a TL works. But your task is to find suitable drivers and cabinet options because I have no idea at all what to look for.
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No ,you guessed it wrong .
because also nanook was on the wrong path .
Whatever signal you may try to feed a loudspeaker to reproduce it , then analyze it with a ...microphone , maybe I'm misleaded , but it is not the right way
to interpretate what is what in music & sound reproduction .
Indeed , there's a long thread about 'measurements & ears '
For example , as far as i know , centers like Kippel that puts lots of
effort in studing motions , materials , rigidity and compliability ,
and have real certified AAA+ laboratories , well ... the final product
is very airy and uncatchable , at least .
So no sweeps ,please
About the story of 'acoustic loads'
I remember that i read the introduction of Ajhorn , and eventually
everything can be explained with the horn theory , as it considers
the acoustical radiation as a combination of ...
well ! Read it ! it's very instructive , and there is also a paragraph about
the TL.
Which I don't think it needs a Phd degree to explain in a few words the
functioning : the cone pressurizes the outside ( useful signal ) and also
the inside ; the mass of air inside is coupled to the movement of the
cone ; this happens till the vibration of the fluid can keep with the
velocity of the cone ( frequency ) ,because air weights , too .
because also nanook was on the wrong path .
Whatever signal you may try to feed a loudspeaker to reproduce it , then analyze it with a ...microphone , maybe I'm misleaded , but it is not the right way
to interpretate what is what in music & sound reproduction .
Indeed , there's a long thread about 'measurements & ears '
For example , as far as i know , centers like Kippel that puts lots of
effort in studing motions , materials , rigidity and compliability ,
and have real certified AAA+ laboratories , well ... the final product
is very airy and uncatchable , at least .
So no sweeps ,please
About the story of 'acoustic loads'
I remember that i read the introduction of Ajhorn , and eventually
everything can be explained with the horn theory , as it considers
the acoustical radiation as a combination of ...
well ! Read it ! it's very instructive , and there is also a paragraph about
the TL.
Which I don't think it needs a Phd degree to explain in a few words the
functioning : the cone pressurizes the outside ( useful signal ) and also
the inside ; the mass of air inside is coupled to the movement of the
cone ; this happens till the vibration of the fluid can keep with the
velocity of the cone ( frequency ) ,because air weights , too .
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