I found the AudioXpress article by Rick Schultz on "alpha" transmission lines very interesting.
The article describes a design method for untapered lines that are completely filled with damping material end to end. The parameters he uses are Fs, Qt, Vas, and Ftheta. That last one requires some explanation. Schultz recommends using a tuning frequency (Ftheta) that is about 1.2 to 1.6 times Fs.
The method produces three numbers: tube length, cross sectional area, and packing density. You may specify either fiberglass or Poly/Acoustastuff. For the latter, when you specify an Ftheta in the range he suggests, the method comes up with packing densities considerably higher than rules-of-thumb that I've seen. The design I'm looking at calls for 1.63 pounds per cubic foot.
I wrote a program to do the calculations automatically, and I fiddled with it until I had a box that was the length I'm looking for. Then I noticed that I had come up with a configuration that was very close to an example in the article!
Driver: Jordan JX92S
Length: 49 in
Packing: 1.63 pounds per cubic foot of Poly fiber
Cross section: 35 in^2
I would be very interested in hearing what the experts have to say about the article in general, and about that design specifically.
I also wonder if Dr. King's method is valid if I substitute a higher tuning frequency for Fs. Fs for that driver is said to be 45Hz. If I use the method in Dr. King's paper "Classic Transmission Line Enclosure Alignment Tables," is the result valid? For this particular example, the numbers come out almost identical if I change Fs as described.
The article describes a design method for untapered lines that are completely filled with damping material end to end. The parameters he uses are Fs, Qt, Vas, and Ftheta. That last one requires some explanation. Schultz recommends using a tuning frequency (Ftheta) that is about 1.2 to 1.6 times Fs.
The method produces three numbers: tube length, cross sectional area, and packing density. You may specify either fiberglass or Poly/Acoustastuff. For the latter, when you specify an Ftheta in the range he suggests, the method comes up with packing densities considerably higher than rules-of-thumb that I've seen. The design I'm looking at calls for 1.63 pounds per cubic foot.
I wrote a program to do the calculations automatically, and I fiddled with it until I had a box that was the length I'm looking for. Then I noticed that I had come up with a configuration that was very close to an example in the article!
Driver: Jordan JX92S
Length: 49 in
Packing: 1.63 pounds per cubic foot of Poly fiber
Cross section: 35 in^2
I would be very interested in hearing what the experts have to say about the article in general, and about that design specifically.
I also wonder if Dr. King's method is valid if I substitute a higher tuning frequency for Fs. Fs for that driver is said to be 45Hz. If I use the method in Dr. King's paper "Classic Transmission Line Enclosure Alignment Tables," is the result valid? For this particular example, the numbers come out almost identical if I change Fs as described.
Dave,
Rick and I have discussed TL theory and fiber stuffing many times via e-mail over the past few years. We discussed his article and I even tried the method before he submitted it to audioXpress. The method works for the type of enclosure he is designing.
But there are many different potential TL alignments, each with its own strengths and weaknesses. When setting up alignment tables for TL's you need to have a few objectives for the finished system. Rick's goal in a finished alpha-TL is different from my goal in my alignment tables. There is no absolutely correct answer, just different compromises.
Yes, my method is valid if you tune to a different frequency. My goal in formulating alignment tables was to make as simple a process as possible, minimum number of calculations required. I made several simplifying assumptions and tried not to require the user to make blind choices that could compromise the design. This is why the driver's T/S parameters are not as prominent in my method. I have received a number of excellent comments and suggestions from many people and will probably update the method sometime this winter. But in its present form, it appears to work quite well. The big advantage over Rick's method is the ability to size non-constant cross-section quarter-wave tubes. This gives the DIYer many more options for enclosure size and shape. Also, I tend to favor lighter stuffing densities in my TL's where Rick seems to recommend higher stuffing densities.
One other request, I have two brothers that can go by the title of Dr. King (one an engineer and the other a Chinese philosophy professor, hey every family has one black sheep) but I cannot lay claim to the Dr. title. I am just Martin or Marty the non-conformist under-achiever.
Rick and I have discussed TL theory and fiber stuffing many times via e-mail over the past few years. We discussed his article and I even tried the method before he submitted it to audioXpress. The method works for the type of enclosure he is designing.
But there are many different potential TL alignments, each with its own strengths and weaknesses. When setting up alignment tables for TL's you need to have a few objectives for the finished system. Rick's goal in a finished alpha-TL is different from my goal in my alignment tables. There is no absolutely correct answer, just different compromises.
Yes, my method is valid if you tune to a different frequency. My goal in formulating alignment tables was to make as simple a process as possible, minimum number of calculations required. I made several simplifying assumptions and tried not to require the user to make blind choices that could compromise the design. This is why the driver's T/S parameters are not as prominent in my method. I have received a number of excellent comments and suggestions from many people and will probably update the method sometime this winter. But in its present form, it appears to work quite well. The big advantage over Rick's method is the ability to size non-constant cross-section quarter-wave tubes. This gives the DIYer many more options for enclosure size and shape. Also, I tend to favor lighter stuffing densities in my TL's where Rick seems to recommend higher stuffing densities.
One other request, I have two brothers that can go by the title of Dr. King (one an engineer and the other a Chinese philosophy professor, hey every family has one black sheep) but I cannot lay claim to the Dr. title. I am just Martin or Marty the non-conformist under-achiever.
MJK said:
For three years I was a visiting associate professor at a midwest university. My students would call me Dr. Jones, but, like Popeye, "I ain't no physiskian." I would ask them to call me Professor Jones, but they would forget. So I asked the chairman of the math department what to do about it. He said, "Accept the title graciously, and take it as a compliment."
MJK said:
I'm so glad to hear that you're working with other thinkers on this. I know from (academic) experience that good ideas and good work only get better when another person gets excited about the technical aspects of a difficult and nuanced science.
I can't wait to benefit even more from your intellectual collaboration, even if the results are from your own work.
I also can't express how much I appreciate your willingness to just give away this kind of work.
Dave
Hi Dave,
Thank you very much for the positive response. Unfortunately, there are some people who are starting to take advantage of my giving away the MathCad worksheets. People have used the worksheets to design and build speakers for profit without remembering the source of the software. In almost all cases, there is not much I can do about this situation.
My original idea, over three years ago, was to supply the worksheets for DIYers to use and provide feedback. This has helped me advance the worksheets alot quicker then if I had just worked on them alone in a vacuum.
So the big question I am now facing is what to do with the next generation of worksheets and the horn theory derivations I am working on right now. I have more to offer on TL design and am becoming very interested in front and back loaded horns. I think the present horn theory could be looked at from a different angle and some new ideas presented. My present thinking is that I will not be freely distributing any more MathCad software and any new work I write-up will not contain all of the engineering details on how I generated the design.
This is very disappointing for me, it has been a lot of fun for the past couple of years and I have interacted with some very interesting people. I would not have gotten this far without these interactions.
Thank you very much for the positive response. Unfortunately, there are some people who are starting to take advantage of my giving away the MathCad worksheets. People have used the worksheets to design and build speakers for profit without remembering the source of the software. In almost all cases, there is not much I can do about this situation.
My original idea, over three years ago, was to supply the worksheets for DIYers to use and provide feedback. This has helped me advance the worksheets alot quicker then if I had just worked on them alone in a vacuum.
So the big question I am now facing is what to do with the next generation of worksheets and the horn theory derivations I am working on right now. I have more to offer on TL design and am becoming very interested in front and back loaded horns. I think the present horn theory could be looked at from a different angle and some new ideas presented. My present thinking is that I will not be freely distributing any more MathCad software and any new work I write-up will not contain all of the engineering details on how I generated the design.
This is very disappointing for me, it has been a lot of fun for the past couple of years and I have interacted with some very interesting people. I would not have gotten this far without these interactions.
MJK said:
That sounds reasonable to me. We have all appreciated your sharing and the sharing of others who have contributed so freely of their labors.
However, no one should blame you for protecting your interests and the investment of your skills and time.
Perhaps you could do some form of limited distribution to those individuals you believe worthy of your trust and who also are at a level to generate interaction back and contribute to further development of concepts, etc.
I can make such a suggestion because I am clearly not a candidate for that but I can think of several people that might be if you were to do something along those lines.
Hopefully that would be win-win except for those that are abusing the situation.
You could set up a Yahoo group and limit the membership to those that you select. You could also set conditions that to remain a part of the group that members agree that they must find an acceptable way to contribute to the group or they cannot maintain continued membership. This could provide for a certain amount of division of labor and more rapid development - all under your leadership. More win-win if it works
Just thinking off the top of my head here.
I'm so sleepy I don't know if this is babbling or brilliant
Off to bed
later
Ken L
MJK said:
If you want to profit from your work (and I would be the last to fault you for that!) I don't think there's much you can do other than to keep your work secret. These days a person can patent just about anything, but enforcing a patent can prove costly or next to impossible. If you do keep the work secret, the challenge is then how to profit from your secret knowledge.
I would like to point out however that the manufacture of quality products for profit is a good thing. If you do not intend to pursue profits from your research, I say make it public, and if others profit, so much the better! In the present case, the world gains not only jobs for productive people, but also good sound for those without the time or skills to design and build their own systems.
To avoid being disingenuous, I should mention mention that I have some general purpose optimization and modeling software that I wrote about eight years ago, intending to publish it in conjunction with a book. But instead I chose to keep it to myself. I have in effect licensed it at no cost to the company I now work for, and in which I hold a sizable equity position.
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