D strings vibrating sympathetically

[amowry]

I currently have one of my mandolins back here in the shop for adjustments, and the owner had mentioned getting an unwanted resonance. It seems to be the D string vibrating sympathetically when notes are played on other strings. I hadn't noticed this much before, but I checked out some other mandolins I have around, and they all do it to some extent, clearly because the body cavity on all is fairly close to a D (within about a half step or so). You can hear this tapping on the top of any of them-- the D string resonates more than the other strings. Indeed, the noise that my customer noticed sounds a bit like someone tapping on the top of the instrument (exciting the D string in the process) each time you play a note on the other strings.

So, any suggestions for alleviating this, or is it just the nature of the beast to some extent? I don't particularly mind it, but I know different people are sensitive to different things.

[the padma]

Sounds (pun intended) like a wolf note. IF so...

Not much can really be done besides some retooling of either the top, braces, back,or linings (in that order)in an attempt to shift the box resonance away from "D". Major big time hassle if its a strap hangin "F'er." Round or oval tops make this much easier. Note that re-tooling don't necessarily mean removal of wood ~ try moveing a clump/s of modeling clay or plasticien on the top...see if that works first...if it does...carve a pyramidal block/s of appropriately equal weight and glue it to the inside of the top in the same place.

Ya there are a few other things that might work....different strings....messing with the bridge design, and the tail piece design, as well as dampers on the after lengths between the bridge and tailpiece. These methods, ideas and techniques suggested will be found in details on the various fourms dealing with wolf notes in the violin family, especially cellos.

Good luck.

Blessings
duh Padma


PS: near forgot...tuning to A @ 432hz would probably solve the problem as well, all though the rest of the band may get bent outa shape about it...however ... the violinist will love it.

[JeffD]

I take advantage of this on my one instrument where this is more predominant. It can be a cool part of the sound.

[amowry]

Thanks for the suggestions-- I did actually reshape the tone bars a bit this morning, with no major change, and I've tried the modelling clay as well, as well as weights on the bridge, etc. I'm pretty convinced that it's a not a mode of the wood that's causing it, but just the fact that the D string is the most resonant one because it is closest to the main chamber resonance, which is at about D +45. I'm also getting convinced that it's not more apparent on this mandolin than on others I have sitting around (not just my own, but from some other makers). It may be partly a case of something getting under one's skin once you notice it and dwell on it. I want to do my best to make my customer happy, though, so I'm open to more suggestions.

[sunburst]

I think it is the size of the thing is the "problem". Tops, backs, other parts all contribute to one degree or another, but as long as we build "normal"-sized, mandolins, the amount of air in them will be about the same, and that will give us a Helmholtz resonance somewhere in the range of D. I'm sure you know at least as much as I do about the relationship between F-hole size and Helmholtz resonance, and how the relationship is geometric, or logarithmic, or exponential or otherwise not 1 to 1 so that opening the f-holes will have only a small affect on Helmholtz. At this point, I believe there's not much, short of major surgery, to be done.
BTW, if you had a "wolf tone", as I understand it, you are correct in thinking it would probably be associated with a body mode, probably a top mode, but in the case of a mandolin, it would be stealing energy from the strings and causing a weak D (or whatever) rather than a profound D. I don't think that's the problem (if indeed there is a problem, and I suppose that is in the ear of the owner, and after all, that's who counts...) so I'm not surprised that modeling clay doesn't locate anything. In this case, I think it is the D strings that are stealing energy from the body (Helmholtz) and that is the ringing that you and the owner are hearing.
Maybe Dave will stop by and straighten me out on all the parts of that that I might have gotten wrong, and shed some light on the situation.

[amowry]

John, I think you're exactly right, and thanks for restating it so clearly, as you often do. My customer read this thread and is fine with me moving on to other things. It is my hope that the resonance will diminish again with time. I would be curious to see if Dave has anything to add, though (thanks Dave!).

[HoGo]

I consider this a normal expected way the archtop mandolins sound. Perhaps changing to different bridge may shift things somwhere. I'd try lighter bridge or heavier one... Or made of different wood or full contact vs. two footer etc. That may change behavior of the transfer of the frequencies from body back to strings... just speculating.

[Philstix]

I don't want to beat a dead horse but did you try damping between the bridge and the tailpiece? A little piece of rubber ( a small grommet works nicely) wedged between the paired strings works and can be moved closer or farther from the bridge to modify its effect. If this noise is due the to body cavity resonance the D will jump when played already and a small bit of damping might even out the sound of the mando a bit.

[mtucker]

yup, most of them do it... a piece of non-green felt or belting (thick enough) behind the nut under the strings should do it, careful with varnish.. dampen behind the bridge w/rawhide, tape, rubber grommets..whatever, if it persists. really dry's up the sound, too convoluted, otherwise. my tailpieces are locking swivels that are felted on the backside, no worries from behind the bridge.

[amowry]

We've dampened the strings both before the nut and after the bridge, but this is the "playing" length of the D string that's vibrating. I'm guessing it's pretty common, and as Adrian and John say, it may just be the nature of the beast.

[Bill Burch]

Also, when you think about common mandolin keys, G, D , and A are at the top of the list. Your D string is the tonic (fundamental) in the key of D, the 5th in G (which is a strong harmonic) and the 4th in The key of A. If that D string DIDN'T ring out, I'd be concerned. Seems like a natural part of the instrument and how it's played.

Bill

[Ivan Kelsall]

It sounds pretty much the same sort of thing that i get when using my clip-on tuner.I tune the G string & the D note registers straight off,i assume for the reasons that Bill Burch states above.It sounds a bit goofy,but to get the G string to register,i have to twang it even harder.I have made one observation though,with my slightly larger than 'standard' Lebeda (compared to my Weber),the D resonance seems to be less ie. it's easier to tune the G string because i don't need to twang it so hard to get it to register.I think that quite a few players have mentioned the same thing on here. I certainly haven't experienced any unwanted vibration in the D strings while playing. There's too much going on with all the other strings vibrating for that to happen (IMHO),
Ivan

[Tavy]

It sounds pretty much the same sort of thing that i get when using my clip-on tuner.I tune the G string & the D note registers straight off,i assume for the reasons that Bill Burch states above.It sounds a bit goofy,but to get the G string to register,i have to twang it even harder.I have made one observation though,with my slightly larger than 'standard' Lebeda (compared to my Weber),the D resonance seems to be less ie. it's easier to tune the G string because i don't need to twang it so hard to get it to register.I think that quite a few players have mentioned the same thing on here.

I suspect that's the tuner picking up the second harmonic on the G string (an octave and a 5th above the fundamental), rather than the fundamental itself. If it bothers you, sound the harmonic on the problem string and the tuner will register the correct note (since all the overtones will be the same note as the fundamental in that case).

As for original question - this does seem to be a fundamental mandolin design issue - short of completely redesigning the F hole mandolin - in which case it would sound completely different - I don't see there's much you can do.

I guess you could try altering that resonance either by part blocking off the F holes (to lower the frequency), or adding some padding inside the instrument to reduce the body cavity size (increase the frequency) and see what effect it has.... but that would be purely an experiment for future reference, not something you could do the instrument in question.

Just my 2c..... John.

[Willie]

Ivan....On some notes it is better to pluck the string with just your finger, a pick seems to confuse them....I find this on the D string a lot, it shows up as an A on the tuner....Other times it is another string doing it so I just tune with my finger and no pick...

Willie

[Kevin K]

Like what someone mention above, maybe doing something with the F holes or something like quilted polyfill on inside ???

[the padma]

Yo, Andrew

Go here.

Same principals apply.


Then surf around for "other types " of eliminators and dampers that only clamp on to one string. There are several out there.


blessings