Spoke pitch frequency
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Been playing with the spoke pitch idea the past two nights for my 2nd and 3rd wheel builds (3rd is actually a rebuild where I replaced the well used factory spokes and rounding nipples with new ones)
One thing that surprises me is that most people who have looked at this seem to be using the entire length of the spoke from nipple to hub. What I find though is that I get the clearest pluck if I damp the crossing spoke with my hand, and then damping the short piece inside of the cross doesn't change anything. So I'm pretty sure what I'm getting is the resonance of the nipple to the primary cross that is actually in contact.
These are 36er wheels, so that distance is 260mm. Neglecting end effects, finding that these 2mm plain gauge spokes pluck at round 410 Hz implies around 117 KgF, which seems like a reasonable number for a heavy (42mm wide, double wall) rim. Additionally if I run the numbers for the entire length (about 350mm out of 369 ordered length) that 410 Hz would imply about 200 KgF, and there's no way that is reality.
Previous times I've done this (including a few weeks back in the field when I got some spoke noises during a climb) I didn't think to damp the crossing spoke and while I could hear some spokes plucked "off" things were much less clear. Damping the other side of the pair seems to remove that dissonance and make the situation of the spoke being plucked a lot clearer.
That said, as the wheel starts to equalize there does seem to be a "choir" effect - I'm damping the paired spoke but there are 34 others free to sympathetically vibrate - the sound does seem to be "better" when each one is tuned so it matches the rest of the wheel.
One thing that surprises me is that most people who have looked at this seem to be using the entire length of the spoke from nipple to hub. What I find though is that I get the clearest pluck if I damp the crossing spoke with my hand, and then damping the short piece inside of the cross doesn't change anything. So I'm pretty sure what I'm getting is the resonance of the nipple to the primary cross that is actually in contact.
These are 36er wheels, so that distance is 260mm. Neglecting end effects, finding that these 2mm plain gauge spokes pluck at round 410 Hz implies around 117 KgF, which seems like a reasonable number for a heavy (42mm wide, double wall) rim. Additionally if I run the numbers for the entire length (about 350mm out of 369 ordered length) that 410 Hz would imply about 200 KgF, and there's no way that is reality.
Previous times I've done this (including a few weeks back in the field when I got some spoke noises during a climb) I didn't think to damp the crossing spoke and while I could hear some spokes plucked "off" things were much less clear. Damping the other side of the pair seems to remove that dissonance and make the situation of the spoke being plucked a lot clearer.
That said, as the wheel starts to equalize there does seem to be a "choir" effect - I'm damping the paired spoke but there are 34 others free to sympathetically vibrate - the sound does seem to be "better" when each one is tuned so it matches the rest of the wheel.
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One thing that surprises me is that most people who have looked at this seem to be using the entire length of the spoke from nipple to hub. What I find though is that I get the clearest pluck if I damp the crossing spoke with my hand, and then damping the short piece inside of the cross doesn't change anything. So I'm pretty sure what I'm getting is the resonance of the nipple to the primary cross that is actually in contact.
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I don't use a tensiometer when building wheels, and I generally don't use pitch, either. I just use feel. My question is: how much pitch variation is OK? I got as much as a minor third (musically speaking) difference between the lowest pitch and the highest pitch I found in the wheel I built most recently.
I'm also a musician with extensive singing and guitar experience, so I can nearly always hear pitch differences that are present, at least I think that! Occasionally after touching up a wheel I get curious about pitch and begin playing my new circular harp with a small screwdriver. I rarely notice revised pitch differences as large as a half-tone, so it seems that a half-tone is kind of a large difference. I'm not sure if a tension tolerance representing ½ tone would result in a wheel that is acceptable from a structural and durability point of view.
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#30
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In the name of science just pulled a 29er wheel out to compare (though it has a large diameter IGH so the proportions are still a little atypical).
Anyway, on this I seem to be able to excite both the whole-spoke and cross-fretted modes. This wheel doesn't "pluck" as well as the long free length of the 36er spokes beyond the cross, tapping the spoke with a wrench seems to excite both modes more. One comes in a bit under 400 Hz the other in the 600's both corresponding to something in the 100-110 KgF range.
I think what I'm concluding from this is that evaluating the big 36er wheel based on the cross-fretted mode is valid, but for something more like an ordinary bike wheel the whole-spoke vibration mode can be apparent, too. A spectral display app is useful for seeing the mix of what it present and putting a number on it (actually works better with the sample rate low), ear is better for comparing spoke to spoke when finger damping can make a particular mode clear.
And yes, while consistency around the wheel is a primary goal, it's also important to have some idea that overall tension is in the ballpark. Part of the reason I rebuilt the factory wheel I'd been riding is that it kept breaking spokes at the elbows - probably from a lot of miles (not just mine but the previous owner's) too loose, and the nipples that never seemed to be an exact wrench size to begin with were rounding off making further maintenance impossible (wrench flats portion broke right off some as I disassembled the wheel). But the goal was not just to replace the worn out and fatigue parts but to end up with something of a proper tension hopefully making it more durable than what I had before.
Anyway, on this I seem to be able to excite both the whole-spoke and cross-fretted modes. This wheel doesn't "pluck" as well as the long free length of the 36er spokes beyond the cross, tapping the spoke with a wrench seems to excite both modes more. One comes in a bit under 400 Hz the other in the 600's both corresponding to something in the 100-110 KgF range.
I think what I'm concluding from this is that evaluating the big 36er wheel based on the cross-fretted mode is valid, but for something more like an ordinary bike wheel the whole-spoke vibration mode can be apparent, too. A spectral display app is useful for seeing the mix of what it present and putting a number on it (actually works better with the sample rate low), ear is better for comparing spoke to spoke when finger damping can make a particular mode clear.
And yes, while consistency around the wheel is a primary goal, it's also important to have some idea that overall tension is in the ballpark. Part of the reason I rebuilt the factory wheel I'd been riding is that it kept breaking spokes at the elbows - probably from a lot of miles (not just mine but the previous owner's) too loose, and the nipples that never seemed to be an exact wrench size to begin with were rounding off making further maintenance impossible (wrench flats portion broke right off some as I disassembled the wheel). But the goal was not just to replace the worn out and fatigue parts but to end up with something of a proper tension hopefully making it more durable than what I had before.
Last edited by UniChris; 02-28-20 at 12:04 PM.
#31
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Tune the front wheel spokes to 98Hz, and the non-drive side to 123.47, with the drive side at 146.83*. Clip baseball cards to your set stays and fork tubes to pluck the spokes, and you're a rolling G major.
*Not sure that these tensions give you proper dish. As an assignment, the student is asked to figure out DS/NDS tensions which (when combined with a front spoke tension, also specified by the student) allow the spokes to give a major chord triplet while providing proper dish.
*Not sure that these tensions give you proper dish. As an assignment, the student is asked to figure out DS/NDS tensions which (when combined with a front spoke tension, also specified by the student) allow the spokes to give a major chord triplet while providing proper dish.
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Back in the late 1970s this topic was covered in Bike World (which later folded into the Bicycling Mag universe). John Allen is both a music instrument service person and an engineer, he wrote of truing by pitch.
At that time I was working for the best, back then, bike shop in the area and we would lace up circus clown wheels with an off center hub (think Ingo rear wheel). The range of tones with the changing spoke lengths was cool to play with. Andy
At that time I was working for the best, back then, bike shop in the area and we would lace up circus clown wheels with an off center hub (think Ingo rear wheel). The range of tones with the changing spoke lengths was cool to play with. Andy
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To determine the limit, try pinging the spokes on the back wheel, gear side. There is tremendous tension there to compensate for lack of leverage. Any snapped spokes will occur here. And it`s a an absolute bugger to change `em . . .! Dunno why they don`t just put more spokes on that side . . . heck, I could do that myself . . .I`ve got 32 to play with . .
God help you if you want to find a high quality 2:1 hub to lace up yourself, though
Last edited by smashndash; 03-15-20 at 08:50 AM.
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Tune the front wheel spokes to 98Hz, and the non-drive side to 123.47, with the drive side at 146.83*. Clip baseball cards to your set stays and fork tubes to pluck the spokes, and you're a rolling G major.
*Not sure that these tensions give you proper dish. As an assignment, the student is asked to figure out DS/NDS tensions which (when combined with a front spoke tension, also specified by the student) allow the spokes to give a major chord triplet while providing proper dish.
*Not sure that these tensions give you proper dish. As an assignment, the student is asked to figure out DS/NDS tensions which (when combined with a front spoke tension, also specified by the student) allow the spokes to give a major chord triplet while providing proper dish.
#36
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You don't tighten your spokes to equal tension to five digits? How can you live with yourself?
Seriously, I just cut and past copied from a table (I don't keep pitch/frequecy tables memorized). That last significant digit is a tenth of a cent (a "cent" being 1/100 of a semitone). This is inaudible.
Seriously, I just cut and past copied from a table (I don't keep pitch/frequecy tables memorized). That last significant digit is a tenth of a cent (a "cent" being 1/100 of a semitone). This is inaudible.
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I went to the dark side and bought a Park Tools tensiometer (on sale) after my first couple wheels. I enjoy being able to have a bit more quantitative approach to the wheel assembly. Park has an on-line app that gives cool graphic illustrations about spoke tension balance.
OT, it was great seeing you at the Massacree after all these years!
Steve
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Even for a ballpark absolute reading it seems like it would be best used to compare a wheel to a fixture with a scale applying a known tension to a spare spoke of the same sort.
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The Park tensiometer is inexpensive and simple, but it gives an indication of tension which can be converted (at least in theory) to actual tension values. Whether these are exactly accurate is less important to me than their consistency. The wheels I've built using the TM-1 have stayed true. YMMV, of course!
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I am a musician and guitarist, repair guitars too. I can easily identify the spoke tensions by pitch. I have a Part TM 1 and it confirms what my ear says. On a regular wheel with DB spokes two spokes of same pitch are pretty much right on on the Part TM. I think I could easily build a wheel on pitch of spokes but of course still have to have the wheel true and in that case all the spokes on one side are not exactly the same.
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You have the concern backwards: crossing other undamped spokes confuses the situation of the one you are plucking, which is why you probably want to damp the crossing spoke so you hear only the one of interest
Which is why it's far less precise than pitch
They aren't unless you currently calibrate it against something, but they're not really precise enough to be accurate at transferring that calibration to a wheel
again, less precise at relative tension than pitch
I get it, it is so tempting to trust a piece of equipment. But something of that design is really not trustworthy, you can readily hear differences it cannot detect
That's more a function of stress relieving and not leaving the spokes twisted, such that many miles down the road they are still at the tension they left your stand with
The Park tensiometer is inexpensive and simple
but it gives an indication of tension which can be converted (at least in theory) to actual tension values. Whether these are exactly accurate
is less important to me than their consistency.
I get it, it is so tempting to trust a piece of equipment. But something of that design is really not trustworthy, you can readily hear differences it cannot detect
The wheels I've built using the TM-1 have stayed true. YMMV, of course!
Last edited by UniChris; 03-02-20 at 08:39 PM.
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I'm happy tuning by pitch works for you; I'm sticking to the measurements.
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When things are very close to being in tune there is a limited "pulling" effect - but notice how you can still hear a dissonance between mismatched undamped crossing spokes because their effect on one another is tiny. When you get them in tune with each other they sound much more clearly.
And with a stiff "string" like a spoke the end fixation reduces the effective length somewhat.
I'm sticking to the measurements.
You may very well build good wheels, but that is because you build good wheels. Many do so with no specific measurement attempt at all.
Last edited by UniChris; 03-03-20 at 10:38 AM.
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#44
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I build good wheels, and I don't use any measurements. Measurement tools were unavailable when I learned. But with that said, I think measurement is a good thing. I just can't tell you how to do it. My wheels don't ping or go out of true.
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#45
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The +-20% tension range is a pretty narrow range, it's less than a full note either way.
For 292 mm 1.8 dia...
391 hz G4 108 kgf
415.3 hz A4 flat 123 kgf
440 hz A4 137 kgf
The note is based on how fast the tension in the material can pull its inertia back and forth, but the algebra assumes a constant section. The butted spoke is thinner in the middle so it might not have pure behavior.
For 292 mm 1.8 dia...
391 hz G4 108 kgf
415.3 hz A4 flat 123 kgf
440 hz A4 137 kgf
The note is based on how fast the tension in the material can pull its inertia back and forth, but the algebra assumes a constant section. The butted spoke is thinner in the middle so it might not have pure behavior.
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#46
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I think we just agree to disagree.