Strings of unequal diameter

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Strings of unequal diameter

Postby GrantOlson » Sat Nov 18, 2017 9:08 pm

I had an interesting idea for an instrument, but am having trouble testing. I have a few questions, and would appreciate any input.
As the title says, I am thinking of a stretched string of unequal diameter. There are two different ideas I had: one was to attach some weight near the bridge, preferably adjustable, and the other idea is where the string would be split, on one side plain steel and the other wrapped like a bass string.
I should make it clear that this would be a fretted instrument. The idea is that with extra weight and properly spaced frets, the instrument could simply behave as if the strings were longer than they actually are. I did some sort of test on a simple one string dulcimer sort of thing I had that was mostly already made. I took a guitar bass string and stripped the winding off to about the fifth fret of the dulcimer. There was a whole lot of buzzing, I'm not sure why, and it made it hard to hear any definite pitch. As best as I can tell, the octave up from playing the open string was found on the 8th fret, not the 7th. So I'm wondering if you can take the mass of the total VSL and average it out to get linear mass density. This is the type of number needed for the formula of the frequency of a stretched string.
So I have a few questions. If anything was unclear please tell me and I will try to help.
1)If I was going to attach a weight near the bridge, I have no ideas. Does anybody else? I think that it could be hard to understand what I mean, but hopefully I can explain. I am really thinking something where instead of having the string partially over-winded, all of that mass would be condensed in one place, which could be moved and would probably affect something but I don't know how. As I was thinking about it, I realized that if it had any significant length it would need to be flexible.
2)Does anyone know if there are strings for sale like the bass strings of an autoharp, where part of it is winded and part isn't? The difference would be that I would want the unwinded part longer.
3)Does anyone know of any formulas that predict how something like this would behave?
I would appreciate any input to this, and again let me know if your just confused :D
Grant
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Re: Strings of unequal diameter

Postby Frimp » Sat Nov 18, 2017 11:00 pm

"Well, that's a peculiar to me, seem like. 'Bout busted m'brains tryin' ter figger her out. Cain't seem to come at it a-tall!
P'rhaps you kin rumble up a feller here what's got some book-larnin', to help you out o' yer miseries..."
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Re: Strings of unequal diameter

Postby danc9 » Sun Nov 19, 2017 2:04 am

Yes, sounds like one for rtroughear!

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Re: Strings of unequal diameter

Postby kwl » Sun Nov 19, 2017 2:59 pm

I'm with John and Dan. I don't really understand the questions or concept. I do have a friend who winds strings and could probably make any string you want. I think you can can specify the gauge of the core wire as well as that of the winding, but I am not sure about this.

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Re: Strings of unequal diameter

Postby GrantOlson » Sun Nov 19, 2017 4:08 pm

Sorry, I was having a hard time describing the idea. I'll put a picture of the experiment I've already done; maybe that will help.
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Re: Strings of unequal diameter

Postby GrantOlson » Sun Nov 19, 2017 6:36 pm

DSC_1006.JPG

The two frets shown on this dulcimer are the fifth and sixth fret, the fifth being on the left. The string continues unwinded to the nut, and winded to the bridge. I put some solder to hold the winding in place, but I still think it's where most of the buzzing comes from.
I'll try to explain my idea again, hopefully more simply. If the entire string was unwinded, like the left side, it would sound at one frequency. With the winding on the one side, it will have more mass, and therefore will have lower frequency. I am very confident in this. However, I am not sure how to predict what the actual frequency will be. The formula for the frequency of a string assumes that the string will have the same diameter at any point on the string, which this does not.
I realize now that I used a couple terms that were unnecessary; sorry about that :oops: I also mentioned fretting a string like this, which is kind of weird to think about and not really important for my questions.
In my original post:
Question 1 was just my raw idea maybe no one will quite get and that's okay :D Number 3 was about if anyone might be able to help me understand this based on a formula or something, and number 2 was about various resources that might be out there. Thank you kwl for suggesting your friend; does he have a website or a way to contact him?
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Re: Strings of unequal diameter

Postby strumelia » Mon Nov 20, 2017 9:10 am

in your photo, when you go to fret on the 5th fret, the fatter portion of the string will hit the 6th fret first, and it will sound the note of the 6th fret instead of what you are wanting. For that reason it will be very problematic, and the solution to that issue will be difficult.
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Re: Strings of unequal diameter

Postby GrantOlson » Mon Nov 20, 2017 10:16 am

Actually, on this dulcimer that doesn't seem to be a problem, but thanks for pointing it out. The bridge on this one is kind of high so that could be a problem on another one.
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Re: Strings of unequal diameter

Postby kwl » Mon Nov 20, 2017 9:07 pm

Grant, here it the string section of Tom Fladmark's website. His contact information is on the site. You can tell him that Ken Longfield suggested the you contact him.

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Re: Strings of unequal diameter

Postby GrantOlson » Tue Nov 21, 2017 1:21 pm

Ok, thanks Ken! I think that buying strings will be a great way to go because it will sound much better than anything I could come up with. I'm going to work on figuring out what sizes I might want and then I will contact him.
For those who are interested I have a theory for the frequency of a string like the ones I have proposed. (Warning: this may be technical). If you look at the formula for the frequency of a stretched string, (http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/string.html), there are really two factors, one is the length of the string, and the other is the velocity of the wave on the string. Then of course there are a couple factors to determine that velocity. However, they depend on the fact that the string is of uniform density. What I would propose is that if you had a string that was divided up into segments, and you knew that each segment was of uniform density, you could determine the frequency of the string. I think you could determine the velocity of the wave in each segment, and then find the average velocity on the entire string based on the lengths of each segment. I am not sure how to test this and I don't know enough about math to know if that would work or not, but if someone does that would be great.
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Re: Strings of unequal diameter

Postby rtroughear » Fri Nov 24, 2017 8:05 pm

Grant
I'm away from home at the moment and haven't looked at my computer fro a week or so, hence the delay.

I don't have any particular insights into the matter - the websites you refer to probably cover it well. You might also have a look at the "String Theory" section of http://www.alcarruthluthier.com/Acoustics.htm for a practical take on string vibration.

Other than the problem that Lisa points to, of action change at the transition from unwound to wound sections, the non-linear string density is almost certain to produce gross intonation problems. Even if you made a dedicated dulcimer with custom fretting to accommodate the non-linear density, you would probably not be able to duplicate the same density distribution on the next replacement string you put on it. I know from my own experience with ukulele strings that the occasional string turns up which has non-uniform density along its length, and it is impossible to play in tune over the whole fretboard. The only solution is to throw it way and put on another one.

If you had a multi-segment string of varying mass/length, there would be multiple transitional areas at the joins where there would be different bending stiffnesses which is the reason to do bridge/nut compensation in the first place. So intonation compensation would be even more difficult than a single-density string. You would have to ask yourself -what is gained by doing this?

The small weight on the string sounds like an interesting idea, but I think it might result in more of a change in tone rather than simulating a longer string - a bit like damping the string end with the side of the hand to produce a short plunky tone. But it's easy to try out,hva a go and let us know

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Re: Strings of unequal diameter

Postby Robin the Busker » Sat Nov 25, 2017 5:14 am

Hi Grant,

Oh I love this type of experimentation! It is just the sort of thinking process that came up with drawn wire and windings for metal strings for zithers some mmmm...... 700 years ago :lol:

What I can't follow in your posts is what your end goal is? I understand your basic premise that adding weight to a string = making it sound longer (lower pitched) than its VSL but I can't understand why a thicker fully wound string wouldn't do that job better than a partial winding - particularly considering the intonation issues it would throw up when fretting the string.

There have been strings produced where the windings do not go all the way the to string's end. This is usually to allow the core wire to contact the bridge and nut rather than the thick windings and so get cleaner vibration transfer to the instrument. Look at bass end piano strings for example that are double or triple wound.

scott-collins-iphoneography-piano-strings.JPG


I can also remember buying a set of acoustic guitar strings where the windings started about 2" from the ball end to allow the core alone to contact the bridge. They were billed as having a more 'country' sound but really didn't sound any 'better' than normal strings. They were a bit too 'twangy' - obviously the more muffled sound of windings crossing the bridge actually suited the instrument better.

I think that 'starting with the end in mind' is often a good way to approach this type of experimentation. First identify the problem you want to solve - and I'm not sure what that problem is in this case? Is it to make a better sounding dulcimer? If so, what do you mean by that?

Robin

PS Don't give up - we would never have had the light-bulb if Edison had given up!
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