Such a wealth of information. Thanks xrk971 and Scottmoose.
Some more questions, if I may.
You both designed mets for the Betsy-K, let's call them variant X (xkr971) and S (Scottmoose).
S is a foot taller than X. X has a slightly smaller top cross sectional area than S, but a much larger base. Ratio of expansion is 10.24:1 for S, and 26:1 for X. Both speakers are placed 36-37 inches off the bottom. X has a 5" x 2.5" vent, while S has the smaller and much shorter 4" x 0.75" (which I believe is just a 4" diameter hole in the base).
The frequency response for S looks smoother, but that could be a function of the models and software. What do you guys use to model these? How do you decide the parameters? Still digging through MJKs paper with the tables for MLQWT speakers, haven't fully understood it yet. My guess is that there are a large number of free parameters if two designs for the same driver could have such differences.
Finally, Scottmoose, I'm trying to join the FH forums, but there has been a tech problem that's being worked on. Looking forward to seeing what you posted there too.
Much appreciation for the info.
Regards,
Martin
Some more questions, if I may.
You both designed mets for the Betsy-K, let's call them variant X (xkr971) and S (Scottmoose).
S is a foot taller than X. X has a slightly smaller top cross sectional area than S, but a much larger base. Ratio of expansion is 10.24:1 for S, and 26:1 for X. Both speakers are placed 36-37 inches off the bottom. X has a 5" x 2.5" vent, while S has the smaller and much shorter 4" x 0.75" (which I believe is just a 4" diameter hole in the base).
The frequency response for S looks smoother, but that could be a function of the models and software. What do you guys use to model these? How do you decide the parameters? Still digging through MJKs paper with the tables for MLQWT speakers, haven't fully understood it yet. My guess is that there are a large number of free parameters if two designs for the same driver could have such differences.
Finally, Scottmoose, I'm trying to join the FH forums, but there has been a tech problem that's being worked on. Looking forward to seeing what you posted there too.
Much appreciation for the info.
Regards,
Martin
There's no frugal-horn forum that I'm aware of.
The metronomes I design, most of which are on the frugal-horn site, are via my own set of alignment which I derived a few years back. I run them through Martin's MathCAD worksheets to provide a set of plots as in the above.
Note that Martin's alignment tables do not cover mass-loaded designs, so are of more limited value for boxes like this. They give excellent background on the physics of QW pipes though, so required reading if you're interested in the subject.
The metronomes I design, most of which are on the frugal-horn site, are via my own set of alignment
Note that Martin's alignment tables do not cover mass-loaded designs, so are of more limited value for boxes like this. They give excellent background on the physics of QW pipes though, so required reading if you're interested in the subject.
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Oops
My bad, it was the forum at Common Sense Audio I couldn't get into. The AN speakers look nice, but the difficulty in getting T/S parameters is somewhat troubling. And they cost a lot more than the Betsy-K speakers.
Also, Scottmoose, could you provide a link to the FH info? I'd like to see what other nuggets of wisdom are tucked away there. And thanks for the warning about MJK's tables not covering mass loading. I'll have to research that elsewhere, but will still work to master MJK's models and concepts.
Finally, I should probably fire up my baffle step program and see what it predicts for these shapes.
Thanks again, all.
Regards,
Martin
My bad, it was the forum at Common Sense Audio I couldn't get into. The AN speakers look nice, but the difficulty in getting T/S parameters is somewhat troubling. And they cost a lot more than the Betsy-K speakers.
Also, Scottmoose, could you provide a link to the FH info? I'd like to see what other nuggets of wisdom are tucked away there. And thanks for the warning about MJK's tables not covering mass loading. I'll have to research that elsewhere, but will still work to master MJK's models and concepts.
Finally, I should probably fire up my baffle step program and see what it predicts for these shapes.
Thanks again, all.
Regards,
Martin
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Martin- exactly what "FH" info are you looking for?
The official web-site
The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs
and there's volumes of posts at both the Planet10 commercial forum and this Full-Range forum
While the plans are "free for personal use" they are subject to terms and conditions outlined here:
Frugel-Horn plans
The official web-site
The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs
and there's volumes of posts at both the Planet10 commercial forum and this Full-Range forum
While the plans are "free for personal use" they are subject to terms and conditions outlined here:
Frugel-Horn plans
Frugal-Horn site
Chrisb,
I've looked over the FH site a fair amount over the last week. That's where I really found out the details of the metronome. What I was looking for was Scottmoose's info about a design for the Betsy-K, per his post (#1079, on page 108) earlier in this thread:
I didn't see it listed in the Metronome-Table. Was wondering if he posted that info anywhere on the site. At this point, my interests are entirely for personal use. Much good stuff on FH, thanks to those who put it there.
Regards,
Martin
Chrisb,
I've looked over the FH site a fair amount over the last week. That's where I really found out the details of the metronome. What I was looking for was Scottmoose's info about a design for the Betsy-K, per his post (#1079, on page 108) earlier in this thread:
I didn't see it listed in the Metronome-Table. Was wondering if he posted that info anywhere on the site. At this point, my interests are entirely for personal use. Much good stuff on FH, thanks to those who put it there.
Regards,
Martin
These things seem popular enough to need a BIB type calculator........
GM
I have not built on of these, but I did do the modeling exercise. I went to the effort to figure the cross section as a true quadratic expansion and used the sections worksheet. While there were minor difference between the between the quadratic and conic expansions, I don't think it is worth the effort. Modeling a metronome as a TQWT is closs enough.
Bob
Bob
How is the Metronome not a conical expansion? Unless the aspect ratio of the rectangular cross section changes from the start to the endpoint, it is conical, AFAIK.
A linear expansion as is typically used in TQWT does differ from conical. By this I mean a wedge shape, as opposed to a cone shape.
A linear expansion as is typically used in TQWT does differ from conical. By this I mean a wedge shape, as opposed to a cone shape.
It's funny and not intuitive at all, but it is conical if two walls are parallel so that expansion is only in 1-dimension. When both sets of walls expand and are non-parallel, it mathematically is a parabolic expansion - that is, the cross sectional area is proportional to a*x^2 where x is axial distance.
Yeah, I understand that perfectly. I guess the confusion is in the terminology. I'm calling the first case 'linear', and the second case 'conical'.
I've always understood conical to mean conic section, as in part of a cone.
In the second case, if both walls are expanding, the cross sectional area is going to be the same as a pure conical section even if the cross section is square or rectangular, as long as the proportions of the rectangle do not change.
I've always understood conical to mean conic section, as in part of a cone.
In the second case, if both walls are expanding, the cross sectional area is going to be the same as a pure conical section even if the cross section is square or rectangular, as long as the proportions of the rectangle do not change.
BTW, I've put the same drivers in equivalent ML-TL, 'classic' TQWT, and quadratic/conical TQWT, and they definitely sounded different. The ML-TL measured best. The conical TQWT sounded best, and better than the classic TQWT. However, the linear TQWT was folded, so it's not a fair comparison. This was just in the process of prototyping. It'd be interesting to do a more controlled test.
I think it may depend on the type of music you listen to that matters. The quadratic/conical may have more harmonics which when playing jazz brass and woodwinds sounds good to my ears. Cello and double bass also sound better than linear expansion or straight expansion. I have also done same driver but different boxes.