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pootsie
09-04-2012, 05:18 PM
Hey all. I just discovered something odd about my uke. It has a nice ringing sustain all over the fretboard EXCEPT for any Ab. G and A ring out nicely on all the strings they go bliiiinnnng! when I pluck them.

But the fret in between them goes thunk. In tune, but thunk instead of bliiinnng.

Is this just a problem with the resonance that cannot be fixed? Is it the strings? I know it is not one particular fret because it happens to Ab anywhere on the fretboard.

Help help.

pootsie
09-04-2012, 06:02 PM
http://www.youtube.com/watch?v=JHmXs35PnE0
Here is a vid showing my problem (and my frustration!)

Please help :uhoh:

pootsie
09-04-2012, 06:48 PM
Thanks for that

I did some googling and it seems like it's kind of the opposite of a true wolf tone. odd. Instead of causing excess resonance, it's like a flat spot.

Right where I wanted to play ... :(

cantsing
09-05-2012, 03:46 AM
Hmmm. Interesting. I have the same Uke, and I totally love the way it sounds when I strum. However, I recently started playing around with fingerstyle, and I began noticing that G# (on every string) goes thunk instead of, as you say, bliiinnng. Same Uke, same note.

I have been thinking of locating a luthier to see if maybe the problem can be fixed or at least improved, but I haven't gotten there yet.

JamieFromOntario
09-05-2012, 04:02 AM
Yeah, it does seem to be an idiosyncrasy with that particular instrument.

I say that this is an opportunity to try some different strings or tunings! Maybe just tuning all your strings down a half step and see if the problem continues, or pick up some different tension strings (here's another plug for SouthCoast mediums or heavies!) and try tuning things down.

cantsing
09-05-2012, 05:32 AM
I say that this is an opportunity to try some different strings or tunings! Maybe just tuning all your strings down a half step and see if the problem continues, or pick up some different tension strings (here's another plug for SouthCoast mediums or heavies!) and try tuning things down.

Good thought. When I first noticed the problem I was using Worth Medium Browns, so I switched to some Worth Medium Clears that I had on hand. It didn't seem to make much of a difference, but they're pretty similar strings. I like your suggestion of experimenting with different tensions. I'll try tuning down, and if that seems to help, then maybe low tension strings will make a difference.

Skottoman
09-05-2012, 05:38 AM
Really interesting. Sorry you're having this issue, but as a sound person who loves physics, it's really interesting!

It would seem to me that the resonance of Ab in that particular uke does not work with the way it's built. The fact that it happens on all strings in different places says it's the construction, and not the frets. Basically Ab is the opposite of the resonant frequency of the uke, and it just does not resonate!

I like the ideas of different strings, and tunings, but if the theory of the uke build is the issue, you will always have a problem with Ab no matter where you play it!

Keep us posted on the change of strings/tuning.
Good luck!
Skottoman

JamieFromOntario
09-05-2012, 05:43 AM
Really interesting. Sorry you're having this issue, but as a sound person who loves physics, it's really interesting!

It would seem to me that the resonance of Ab in that particular uke does not work with the way it's built. The fact that it happens on all strings in different places says it's the construction, and not the frets. Basically Ab is the opposite of the resonant frequency of the uke, and it just does not resonate!

I like the ideas of different strings, and tunings, but if the theory of the uke build is the issue, you will always have a problem with Ab no matter where you play it!

Keep us posted on the change of strings/tuning.
Good luck!
Skottoman


I wonder if tuning up or down by a quarter tone would fix the problem. That way there would be no Ab no matter where you play on the fret board.

It would make playing with others a bit of a challenge...

stevepetergal
09-05-2012, 05:59 AM
I'd list this on the Luthier's Lounge. Sounds like something's keeping the soundboard from vibrating effectively at that frequency. Have you tried tuning up or down? I'd give it a shot. If you go with a half step, and the enharmonic equivalent (Ab at a different location) does the same thing, you know it's just such a deficiency of the instrument. Examples: Go up a half step and you can test the G string open. Down a half step and you can test the A string open. (I would try both)
If the problem continues at the Ab frequency, I would try tuning it in between. The problem may be sufficiently limited that there is a "sweet spot" somewhere in there. Of course you'd be stuck playing solo, unless you played with others willing to de-tune along with you.
One other thought, if you have a pickup on your instrument, I'd remove it and see if the problem goes away. If so, you know the culprit and you can either go without or try changing pickup style or brand.
No results, take it to a pro, for sure.
I'll keep an eye out. Please let us know what you find out, or don't find out.

pootsie
09-05-2012, 06:13 AM
Thanks guys. I posted over at the LL.

I will keep you informed

cantsing
09-05-2012, 06:19 AM
I just experimented with the E string. When I tune down a half step, the thunk moves up one fret along with the Ab. And, predictably, when I tune up a half step, the thunk moves down one fret along with Ab.

No pickup to remove.

I'll keep an eye on Pootsie's thread on the LL.

pootsie
09-05-2012, 06:23 AM
I just experimented with the E string. When I tune down a half step, the thunk moves up one fret along with the Ab. And, predictably, when I tune up a half step, the thunk moves down one fret along with Ab.

No pickup to remove.

I'll keep an eye on Pootsie's thread on the LL.

So you also have a Mainland mahogany slot-head concert?

cantsing
09-05-2012, 06:30 AM
So you also have a Mainland mahogany slot-head concert?
Yes indeed.

I tried to reply simply "yep," but it appears there is a 10 character minimum for a post.

pootsie
09-05-2012, 06:43 AM
I fell in love with that uke online, and finally got to hold her in my arms at UWC this year. Oh, what a summer! What a romance!

There is that point in every love where the first blush fades and reality sets in.

I am still in love with that uke but we need to work on our relationship.

cantsing
09-05-2012, 07:53 AM
I am still in love with that uke but we need to work on our relationship.

I really love mine too, and I'm one of those rare monogamous ukulele players, so I won't give up on this one without a fight.

pootsie
09-05-2012, 07:55 AM
Haha. My first love still visits when I ride my unicycle!

stevepetergal
09-05-2012, 08:08 AM
Did you try between (higher than Ab but not G or lower but not A)? There may be a spot that works.

pulelehua
09-05-2012, 09:08 AM
It sounds like you're getting some sort of phase cancellation. That would most likely be where two relatively flat surfaces oppose each other (so you get parallel reflective surfaces). The sound wave in question (Ab) meets its inversion in near perfect phase, and they partly cancel each other out.

The most obvious situation is that some point of rigidity in the top is the distance (wavelength) from the rigid back of some octave of Ab. The wavelength for Ab0 is 1320cm. So, reducing down geometrically, you're looking for parallel surfaces 10.3125cm apart, or a tiny bit over 4".

Jamie's suggestion of detuning slightly is probably your only solution, and as he says, you'll have trouble sounding in tune with others.

cantsing
09-05-2012, 10:43 AM
Did you try between (higher than Ab but not G or lower but not A)? There may be a spot that works.
Yes, I can definitely move the thunk around, which means I can, as has been suggested, retune/detune so that the thunk sits out of the way between halftones. Or I can just learn to live with it. Or I can try new strings. Or I can pursue it with a luthier--the guys in the LL are chiming in on Pootsie's thread about this same issue.

OldePhart
09-05-2012, 12:28 PM
I've seen this happen even with solid body electric guitars where, even unplugged, there is just a completely dead note. As others have said, it's almost certainly related to the design of the uke, especially since you're seeing it on two of them.

I just checked my Mainland mahogany slot-head tenor and it is fine, but it is the one with a cutaway and rope binding (i.e. it's not the same model, really, at all).

John

OldePhart
09-05-2012, 12:47 PM
Two things possibly worth trying...

1) - try putting a piece of foam inside the uke - if the problem is a standing wave within the body cavity this might change it and move the dead note. Folks who build speaker cabinets use various types of foam and fiber materials to change the characteristics of a cab. Basically, these materials make the effective volume of the enclosure larger by slowing down the sound waves. So, if the problem is a standing wave you can probably change it this way.

2) - use a little bit of blue tac to attach a small weight (maybe a quarter or nickel) at different points on the soundboard. If it's an issue of the top and bracing then that might change the way the top vibrates and, again, move the dead note.

The above are more diagnostic than treatment - but if you can move the dead spot to between notes then you could play with others in standard tuning...

John

cantsing
09-06-2012, 04:34 PM
2) - use a little bit of blue tac to attach a small weight (maybe a quarter or nickel) at different points on the soundboard. If it's an issue of the top and bracing then that might change the way the top vibrates and, again, move the dead note.

John, all I can say is WOW! :bowdown: That, and thank you!

Right now, I have two pennies taped to the top of my ukulele, and the situation is vastly improved. The thunk is no longer noticeable on the Ab, and if it has moved elsewhere, it's much more subtle.

I know some people are curious about this, so here's a picture. The pennies are located at the red dots, close to, but not touching, the bridge.

42669

The pennies don't have to be split up--two pennies stacked on one side of the bridge will produce the same result, but I prefer the symmetry. If I have to, I can live with the pennies. To me, a quirky decoration is much more desirable than a thunk!

Still, I'd be interested -- does anybody have any thoughts about what's going on here and whether this information can be converted into a less visible solution?

Fermin
09-06-2012, 06:13 PM
does anybody have any thoughts about (...) whether this information can be converted into a less visible solution?

Yes, get someone with small hands to tape those pennies on the inside.

Teek
09-06-2012, 11:23 PM
So THAT is what that THUNK is! I have a soprano like that.

Wow @ John

& pennies = brilliant

OldePhart
09-07-2012, 08:23 AM
Heh, heh - sometimes I get lucky. :) Actually, I was pretty sure one of those two things would make a difference in the way the uke responded I just wasn't sure how much fiddling it would take to get it right, or whether it would be possible to get the dead spot completely away from the musical notes.

The issue pretty much had to be either a standing wave in the body or the top vibrating exactly out of phase with the string - either of which would pretty much kill the note.

As somebody said, I'd move the pennies inside the body. Get a bit of double-sided carpet tape - that stuff is thin but adheres very aggressively. Next time you change the strings use a "third hand" (or a bent coathanger with a bit of that blue-tac holding the penny to the end) to put the pennies inside the body - probably on the bridge plate since it looks like they're over the bridge plate where you have them now.

As for what's going on - I 'm a software engineer not a mechanical engineer but basically when anything vibrates it does so in waves - you can see this if you look at super-slo-mo video of vibrating strings and the like. So, different parts of an object are in different phase relationships to the source (i.e. in the case of a stringed instrument each part of the top is vibrating at some phase relationship to the string). The phase relationship depends on, among other things, the frequency (and, generally speaking, multiples of it are going to result in the same relationship). So, it sounds like what was happening is the top was vibrating such that the part of it immediately under the bridge was very nearly exactly out of phase with the string, thus canceling it. Adding (or subtracting, but that's harder) weight at the right point moves the frequency at which that cancellation occurs. You probably still have a dead spot, but now it is either between notes or perhaps completely out of the range of the instrument (actually, all instruments will have dead spots, it's just that they usually are not within the range of the instrument and certainly not right on a "concert pitch" note).



John, all I can say is WOW! :bowdown: That, and thank you!

Right now, I have two pennies taped to the top of my ukulele, and the situation is vastly improved. The thunk is no longer noticeable on the Ab, and if it has moved elsewhere, it's much more subtle.

I know some people are curious about this, so here's a picture. The pennies are located at the red dots, close to, but not touching, the bridge.

42669

The pennies don't have to be split up--two pennies stacked on one side of the bridge will produce the same result, but I prefer the symmetry. If I have to, I can live with the pennies. To me, a quirky decoration is much more desirable than a thunk!

Still, I'd be interested -- does anybody have any thoughts about what's going on here and whether this information can be converted into a less visible solution?

cantsing
09-08-2012, 03:34 AM
As somebody said, I'd move the pennies inside the body. Get a bit of double-sided carpet tape - that stuff is thin but adheres very aggressively. Next time you change the strings use a "third hand" (or a bent coathanger with a bit of that blue-tac holding the penny to the end) to put the pennies inside the body - probably on the bridge plate since it looks like they're over the bridge plate where you have them now.
Sounds like a plan! Thanks so much for the help and the information.

Doc_J
09-08-2012, 04:00 AM
That was less expensive than having the Steve Perry's MandoVooDoo service, which I heard really does wonders.
http://www.mandovoodoo.com/

beautifulsoup
09-08-2012, 02:34 PM
This is a fascinating thread.

Sorry, that's all I've got.

Except for this: :2cents: ;)

(Heh, sorry - I couldn't resist).

pootsie
09-09-2012, 09:39 AM
John, all I can say is WOW! :bowdown: That, and thank you!

Right now, I have two pennies taped to the top of my ukulele, and the situation is vastly improved. The thunk is no longer noticeable on the Ab, and if it has moved elsewhere, it's much more subtle.

I know some people are curious about this, so here's a picture. The pennies are located at the red dots, close to, but not touching, the bridge.

42669

The pennies don't have to be split up--two pennies stacked on one side of the bridge will produce the same result, but I prefer the symmetry. If I have to, I can live with the pennies. To me, a quirky decoration is much more desirable than a thunk!

Still, I'd be interested -- does anybody have any thoughts about what's going on here and whether this information can be converted into a less visible solution?

I've been away from internet access for a few days but have experimented by holding my thumb over various bits o the soundboard and plucking, and I have found that right next to the bridge like in your picture changes the sustain dramatically. I am going to try to get my 2-year-old to stick some coins in there ;)

cantsing
09-09-2012, 11:09 AM
Pootsie, glad to hear you had the same result.

The pennies near the bridge are starting to grow on me. Maybe I'll just stick one on the headstock to match and call it good! :D

daz
09-12-2012, 05:24 AM
first for all, thanks to this thread i was able to finally to understand the weird thing going on with my open E string.. it also does this "thunk" sound with an E note.

I have a Kamaka HF-3(high G) and from this forum also that resonant frequency or wolf note thingy happens on the E note for this uke. So i tried blu-tack + 1 coin(penny-sized) fix here, the best spot for my uke is beside the bridge. It effectively eliminated the "thunk" sound, but the side effect is that it darkened the sound of my uke. The darkening is highly noticeable on the A string.

I felt like it killed the sweet voice of my uke, so i took it off after hours of testing.

Anybody observed the same side effect?


daz

cantsing
09-12-2012, 06:54 AM
I felt like it killed the sweet voice of my uke, so i took it off after hours of testing.

Anybody observed the same side effect?
Sorry to hear that, in your case, any improvement came with too high a cost.

When I found the spot that improved the thunk, I kept moving the pennies on and off the body to see if the overall sound of my uke changed. I thought that maybe the sound was slightly muted with the pennies on, but I wasn't sure. It certainly wasn't enough to bother me.

And any overall sound issues I'm having are probably compounded by my strings. Before this adventure started, I was thinking that my strings might be losing some of their pazazz, which means that they really need to be changed.

pulelehua
09-12-2012, 09:20 AM
Any time you dampen the top of a stringed instrument, you're going to lose sound, or more correctly, frequency response. The sounds you will lose first are the highest pitched overtones. The more damping, the more overtones lost. The highest overtones could be described badly as "crispness" while the lower high overtones are what we might, again badly, call "bell tones". The more of these you lose, the darker the tone will become, and likely, the more attack you'll lose, as the highest frequencies happen at the moment of attack. High frequencies are very short, and are therefore easily absorbed.

Different frequencies vibrate with different efficiency at different points (due to complications based on nasty things like waves, standing waves, nodes and phase reinforcement and cancellation). It would be incredibly hard to map out an instrument top without 1000s worth of equipment, which is why most people use coins and blu-tack.

You might find some spots where you lose less high end, but you're definitely going to lose a bit. It also depends on how good your hearing is, as some of these overtones can't generally be heard by older people (no offence, just physiology!), or by people who have blasted their eardrums to pieces for years.

So, if you don't like the best result you can come up with, go to an AC/DC concert. You'll wake up unaware that there is any problem at all... :)

Freeda
09-12-2012, 09:24 AM
I don't follow all this sonic talk. I just wanted to say that every time I see the title of this thread I think it's a problem with abdominal muscles. :o

cantsing
09-12-2012, 09:37 AM
It also depends on how good your hearing is, as some of these overtones can't generally be heard by older people (no offence, just physiology!), or by people who have blasted their eardrums to pieces for years.
Also, as I probably should have mentioned in my response above, some of us don't have a good ear to start with, and I count myself in that category. And, although I don't generally think of myself that way, I suppose I qualify as an "older person." So maybe I'm just happily oblivious.

pootsie
09-12-2012, 10:21 AM
I tried taping a small magnet (about the weight of two pennies, give or take a smidge) on one side of the bridge. It helped my Ab sustain a lot, and I did not notice any massive decrease in any other resonance. I'm pretty sure that using a damper on just one side would help reduce the loss of the higher harmonics since the other side could still react to them. It would act more like a varied bracing pattern that way ... I think.

I'm going to experiment with moving it around before I go for a permanent addition, but in my case I think a minimal loss of a few harmonics might be worth the trade. I also have Aquila strings, and I hear talk that other brands of string might give it more punch anyway. I'm looking at you, Living Water.

OldePhart
09-12-2012, 12:08 PM
It also depends on how good your hearing is, as some of these overtones can't generally be heard by older people (no offence, just physiology!), or by people who have blasted their eardrums to pieces for years.

Especially the latter. I remember about eight years ago I went over to a friends house to jam in his studio that he'd built above his garage. He only had one guitar amp and I hadn't brought one so he had me use his Mesa and he plugged his Strat straight into the board and was playing through full-range PA speakers with big horns - one of which was pointed right at me. I was like, "dude, are you trying to kill me with that icepick?" and he was "huh? what are you talking about?" He'd fronted rock bands for so many years he had no high-frequency hearing at all.

It's amazing I have any hearing after as much time as I've spent at the range - just goes to prove that custom ear protection is worth the money...

John

daz
09-12-2012, 03:23 PM
cantsing,pelelehua and the rest of the gang..thunks for sharing your thoughts

pelelehua, i really dig ur explanation with the darkening of the uke's tone

ill give the dampening one more try over the weekends..sweet overtones vs E note thunk. but currently leaning towards keeping the distinct kamaka tone

for the strings, im using a 2 weeks old aquila nylguts. i have south coast mediums in transit, will see if it somehow eases the thunk


dAz