I attempted my first transmission line design and it is folded only once. I measured it deliberately without any filling to see if the driver placement is completely eliminating the 3rd harmonic. (Around 1:5 taper, 0.336 according to MJK's alignment tables.) Judging from the impedance curve, it isn't.
My struggle has been, around the fold, how is the "length" measured? Do I take the "midline" of the fold? And also the 0.336 driver placement should be on the midline? (I had an octagonal turn.)
My struggle has been, around the fold, how is the "length" measured? Do I take the "midline" of the fold? And also the 0.336 driver placement should be on the midline? (I had an octagonal turn.)
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I've never heard of this. Why would a specific folding eliminate 3rd harmonic distortion?
I know that push-pull can lower 2nd harmonic, and bandpass boxes can lower *all* distortion. But what you describe, I am not familiar with.
I know that push-pull can lower 2nd harmonic, and bandpass boxes can lower *all* distortion. But what you describe, I am not familiar with.
Thanks for your reply. I realized I used a confusing title by mistake but what I actually meant was 0.336 driver placement was supposed to eliminate the third harmonic (but wasn't for me), and folding makes it hard to measure the length of the line and the position of the driver placement. Hope this makes things clear. Thank you!
You measure the line's length down the middle of its area from end to end including around the fold, and there are two optimum locations for a driver in a line, at 20% and at 33% of the line's length from the line's beginning. Tapering a line definitely helps to smooth the overall response, as does adding stuffing.
Paul
Paul
Thank you Paul.
However I am about to admit defeat that my first TL project has flunked. I had a problem with the 5th harmonic but I am not able to get the TL measurably better than sealed. The only way to get the TL flat is to stuff a lot, killing any bass augmentation, but still, simply covering the terminus would make it even flatter.
Right now my driver is at about 1/3 so maybe moving it to 1/5 might help, but I am afraid the 3rd harmonic will come back with full force and I will be simply moving the problem around instead of solving it.
What stuffing material should be used? Ideally highly resistive at 300Hz but leave 100Hz and below alone.
However I am about to admit defeat that my first TL project has flunked. I had a problem with the 5th harmonic but I am not able to get the TL measurably better than sealed. The only way to get the TL flat is to stuff a lot, killing any bass augmentation, but still, simply covering the terminus would make it even flatter.
Right now my driver is at about 1/3 so maybe moving it to 1/5 might help, but I am afraid the 3rd harmonic will come back with full force and I will be simply moving the problem around instead of solving it.
What stuffing material should be used? Ideally highly resistive at 300Hz but leave 100Hz and below alone.
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To help you we need to know a lot more about the driver you're using and your TL design. I can fairly quickly replicate your design using Martin King's worksheet for the modeling, which will be more accurate than using his alignment tables (which are pretty good). Provide a link to or a listing of the driver's T/S values for fS, Re, Le, Bl, Sd, Vas, Qes and Qms, and describe the line's dimensions (length and beginning and ending areas). For stuffing material, Martin's worksheets and alignment tables are valid for only polyester fiber, like pillow stuffing or Acousta Stuf.
Paul
Paul
I would like to thank all the respondents for your help which is very much appreciated!
Fs is 63Hz. I measured the line length again now that I know mid-line is the correct method and it is 1.37m. Driver position is 0.336 (0.46m). The taper is contracting (CSA at exit is smaller). My simulator was Lenard Audio TL, but the measured ripples are worse than predicted. Fill was polyfill pillow stuffing and I tried 0.2lb/ft3, 0.4lb/ft3, 0.6lb/ft3 and 0.8lb/ft3.
The lack of bass augmentation is owing to an undersized enclosure volume - would have been the same for example in a bass reflex enclosure of insufficient volume.
My first iteration was a sealed design. I was happy except for dip in the midrange which was exacerbated by a similar dip in the crossover response. (A sealed box was not immune to standing waves, either.) The TL did not cure the response, if anything it was made slightly worse, but it had the advantage of moving it away from compounding with the crossover dip.
As I calm down from my initial disappointment I think the only real problem is to adjust my expectations. I expected the TL to blow the sealed box away, but it didn't. I did not give it enough box volume to shine, and what little remained of the bass augmentation got eliminated by the extra stuffing required to cure the ripples.
I do plan to experiment again with driver at 0.2.
Thank you again for the help.
Fs is 63Hz. I measured the line length again now that I know mid-line is the correct method and it is 1.37m. Driver position is 0.336 (0.46m). The taper is contracting (CSA at exit is smaller). My simulator was Lenard Audio TL, but the measured ripples are worse than predicted. Fill was polyfill pillow stuffing and I tried 0.2lb/ft3, 0.4lb/ft3, 0.6lb/ft3 and 0.8lb/ft3.
The lack of bass augmentation is owing to an undersized enclosure volume - would have been the same for example in a bass reflex enclosure of insufficient volume.
My first iteration was a sealed design. I was happy except for dip in the midrange which was exacerbated by a similar dip in the crossover response. (A sealed box was not immune to standing waves, either.) The TL did not cure the response, if anything it was made slightly worse, but it had the advantage of moving it away from compounding with the crossover dip.
As I calm down from my initial disappointment I think the only real problem is to adjust my expectations. I expected the TL to blow the sealed box away, but it didn't. I did not give it enough box volume to shine, and what little remained of the bass augmentation got eliminated by the extra stuffing required to cure the ripples.
I do plan to experiment again with driver at 0.2.
Thank you again for the help.
The figures below depicts the effects of folding a tapered TLS.
One fold really supress the the third harmonic a lot, this means that this geometry reduces the need for damping of harmonics by fiber material..
Did you stuff the whole pipe or just the first part?
One fold really supress the the third harmonic a lot, this means that this geometry reduces the need for damping of harmonics by fiber material..
Did you stuff the whole pipe or just the first part?
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For starters, can you provide the set of more analytic plots shown in my 17-foot pipe thread. That way we can see whats the driver is up to, the port, and together.
17 foot pipe sub 12-230 Hz ±5dB
Best to think in terms of sequestering the rear wave. Forget the "theory", such as it is. You want to squash everything in the pipe except the fundamental. As my plots show, stuff plenty.
B.
17 foot pipe sub 12-230 Hz ±5dB
Best to think in terms of sequestering the rear wave. Forget the "theory", such as it is. You want to squash everything in the pipe except the fundamental. As my plots show, stuff plenty.
B.
You haven't as yet provided all of the data about your TL design and the driver as requested (see my Post #7) and several people would definitely like to help you. Still a driver with an fS of 63 Hz is unlikely to provide much bass regardless of the type of box you put it in or how big the box is.
Paul
Paul
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