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Hi all,

I am one of those guys that has been reading this forum for a while but havent had anything intelligent to ask or add yet. Here comes my first question.

I have built about 35 ukuleles over the last year or so. They all have soundholes on the soundboard in addition to side soundports. Most of them have great sounding clear ringing tones on every note of the fretboard. However, there are a few that have one or two notes that are muted, and without sustain. When there are less than ideal notes, they are always on the 3rd string, and always between the 2nd and 5th fret. Is it likely that this could be an interference with the "main body resonance"? If so would increasing the size of the side soundport slightly affect the "Main body resonance" enough to make a difference? What are other likely causes for notes that dont sound as good as the other notes on the fretboard?

I realize this is a somewhat loaded question, but I think it applies to guitars as much as any other instrument.

Thanks in advance.

Take care,
Thomas

Man, that's a tough one....

I don't think you can ever control this kind of thing completely. There's always a little luck in there somewhere...!

Trev

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http://www.PeakeGuitars.com

It's possible that the neck resonance could be contributing to this also.

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Jim Watts
http://jameswattsguitars.com

Guitar acoustics are so complicated it would be hard to nail it down to just one particular thing.
What we can know is that when a note is dead on an acoustic guitar, the string energy at that frequency is being rapidly dissipated somewhere in the instrument. Some aspect of the guitar is absorbing the energy and preventing it from resonating. It couls be inherent in the particular pieces of wood, or there may be a lack of acoustic coupling somewhere, or a little of both.

My experience with guitars leads me to believe that good solid wood joints in all areas are crucial for energy transmission.

Here's a thought. I've noticed that after closing the soundbox and before routing for binding, if I tap on the box, it produces a clear tone, like a drum in some ways. Sometimes it's a solidly fundamental tone like a maple tom tom tuned to it's resonant frequency, sometimes it's a low thump that hits me in the chest, with clear trebles. sometimes both with degrees in between, but always a clear well defined tone. After routing the binding ledges, the tone disappears and the box becomes a dull thud with with no resonance whatsoever.
I've never strung up a guitar at this point to see what it sounds like, but I'd imagine that it would sound pretty dead.
After binding and purfling, the tone is always restored, sometimes even stronger than before.
I would imagine that a sloppy binding joint could be made to look good and tight on the outside, but if the inside of the joint is sloppy, or has gaps in places you cant see, then the acoustic coupling of the backs and sides is interrupted in places. This might be one source of dead spots and note dropouts in my thinking.
I also believe that excellent kerf joints are equally important for acoustic coupling. A combination of sloppy kerfs and poor binding glue joints would be fatal!
It also makes me leary of using plastic bindings and purflings.
Anyone else have this type of experience?

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Old growth, shmold growth!

There's only one way to solve this sort of problem: figure out exactly what's wrong. I don't know enough about ukes to have much of a picture of where the resonances are, so I can't say what the problem is. It's not that hard to make the measurements, though.

I'll reiterate something I say pretty often: data is your friend. If you think about how the instrument works (or how you think it works) that will suggest some things that you might want to keep track of. If you believe that tickling the strings makes leprechauns laugh, then think of ways you might count leprechauns, and keep track of how many there are in your instruments. After a while you'll be able to say whether the 'leprechaun model' has any merit.

At this point you've made a number of instruments, some more successful than others. If your memory is like mine, you probably can't recall all of the changes you've made. If you had that stuff written down, you'd be in a better position to say what the issues are, or, failing that, you could at least ask some more specific questions.

The 1st place I would look is too much coupling between top and back. By that I mean the top and back resonate at the same frequency. It could be pretty easy on an uke since bracing is minimal or almost inexistent, and the chances of having a top and back ring like clones is strong. Two solutions: add mass to one plate (the back usually), or remove mass by shaving braces. Small increments, of course, restring and listen.
No. What are sloppy kerfs?

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Kerfing is the web of mahogany (or other wood) glued onto the inside edge of the sidesto increase the surface area for gluing the top and back onto the guitar.

If insufficient clamping pressure is used, the kerf may not be tight along it's full height at any given point, or may be attached except by an adjacent portion of kerf webbing, leaving gaps or gaps filled with glue.
I am of the opinion that these conditions can lead to a lack of strong acoustic coupling.
Ideally, the kerf should be like any other glued joint, as tight as possible, so that when sanded, the top of the kerf where the plates are glued and the side of the instrument should look as one.
A mahogany side and a mahogany kerf should look like one piece of mahogany.
Obviously a mahogany kerf and a rosewood side can't look as one, but a visible glue joint where you can see the glue in the seam is less than ideal.

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Old growth, shmold growth!

Kerfing.

Here's a link to the Luthier's Mercantile page where they sell "Kerfing".

http://www.lmii.com/CartTwo/thirdproduc ... er=Kerfing

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Old growth, shmold growth!

Thanks for all the advice, and food for thought.

Laurent, I think you may be on to something. Most of my instruments are concert and tenor size, so they do have some bracing, but it is extremely minimalistic. It is likeley that the coupling is too close as you mention. I may try to put some blue sticky tack on the back jsut to see if the added weight changes anything.

All of my instruments are unbound, so that isnt the problem.

One extra bit of information. If I tune the instrument down a half step the strange note moves down a fret. A whole step and it moves down 2 frets. So it is something with that frequency. It isnt horrible sounding, it just isnt as clear or with the same sustain as the rest of the notes. On a factory instrument it would still be considered a good sounding note by most. Unfortunately I am not happy with that level of sound on even one note on my instruments.

Thanks again, and take care,
Thomas

While I'm no expert, here's some food for thought. I've been using a chromatic tuner to track the "note" that the top makes when tapped.

Something I've noticed is that if the top rings right on a note, say, G, then the open G string will sound awful.

I recently rebuilt my second classical. I took the back off and shaved about 7 grams off of the braces. I kept shaving braces until the "tap note" was halfway between F# and G. It was around A# when I started. After re-assembling, there are no dead notes. All the notes on the G string sound great. In fact, the guitar sounds much better all over, and the dead notes that were there before are gone.

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Regards,
Phillip Patton

http://www.pattonblades.com

The bitterness of poor quality lingers long after the sweetness of low price has faded.

https://hoosierbladesmith.wordpress.com

Thank you, Todd, coffee all over my screen ...


Humpty Dumpty appears to have gotten a position as copy writer for the LMI catalog ...

thomas wrote:
"One extra bit of information. If I tune the instrument down a half step the strange note moves down a fret. A whole step and it moves down 2 frets."

That's the 'smoking gun' that links this to a resonance of the body or air: you moved the string pitch, but the resonance that's causing the problem didn't move.

If you tap on the top at the bridge the sound you hear will most likely be the 'main air' resonance. It's usually lower in pitch than the 'main top' resonance (although I can't say for sure on ukes), but because of the way yuor hearing works you'll 'hear' the lower mode. If you can't match it up directly, try lying the instrument on your lap face up and pinching the lowest string between your thumb and finger near the nut. If you pluck that string you should hear a pitched 'thunk'. Move the pinch point around tyo find the loudest 'thunk', and that's your air resonance pitch (assuming the lowest string on the uke is tuned lower that that).

If you block the soundhole with your hand and tap on the bridge you should hear the 'main top' pitch. Similarly, if you block the hole and tap the back, you'll hear the 'main back' tap tone pitch.

Often a 'wolf' in the low range occurs when the 'main air' mode is very strong, and agrees with the played pitch of the note. There are other 'wolf' notes in the mid-range on guitars that occur when the 'main top' and 'main back' pitches are too close: usually less than a semitone apart. Once you find the main body and air pitches, and figure out how they relate to the 'wolf' you can usually come up with a solution.

Last time I ordered Linings they sent me garbage bags.

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Old growth, shmold growth!

Thomas,
Is down a fret toward the nut or the bridge in your statement?