String theory: more questions than answers

[NeverSayDai]

Here's a curious query for any theorists out there...

 

Looking on the rest of the HC website I cam across a news item:

http://news.harmony-central.com/Newp/2007/Carlos-Acoustic-Strings.html

(repeated below)

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So my question

[totamus]

Well, not to be rude, but this sounds like pure BS. Any string exhibits different tonal qualities depending on where you pluck. You will frequently see players move playing position closer or further away from the bridge for that very reason. So the claim is undoubtedly true, but trying to say this is something new or different is the pure BS part.

[Freeman Keller]

A vibrating string is an incredibly complex mathematical phenomena and I don't pretend to try to understand it. It typically vibrates from its end points as one node (the primary frequency) determined by length, density, stiffness, probably modified by the wound portion moving against the hex core - then this is complicated by the harmonic nodes which colors that tone. The for a fixed bridge guitar (most flat top acoustics) the string alternately stretches and compresses, pulling the top edge of the saddle which rocks the bridge back and forth (there is little if any up and down or side to side motion at the endpoint of the string at the saddle). Of course that is completely different with a floating bridge instrument (archtop, violin, mandolin....) which does vibrate at the bridge.

 

I have never really understood how the composition of the string colors the sound so dramatically but had always assumed it was a combination of the stretching characteristics (different alloys will elongate/compress at different rates) possibly combined with the composition influencing the nodal points for the harmonics. I'm sure there have been mathematical analysis of this but I'm not going to wade thru it all.

 

Does Mr Carlos have some new breakthrough - I doubt it. String manufacturing has been pretty well developed over many years and is being constantly tweaked, but rarely innovated (coatings were the big innovation). But I found the pop ups so obnoxious that I didn't waste much time trying to figure out what Mr Carlos is talking about. If he would like to send me a couple of sets I will add them to the Great String Test at the Annex, but until then, I say

 

BS

[guitarist21]

In addition to totamus and Freeman's responses...

 

 

By plucking at different points on the string he participates in this process with his personal playing dynamics. In musical terms, the pitch of the note is always the same but the tonal quality can be adjusted: our strings respond actively to a players touch, making your musical identity be a happening.

 

 

...this is part of what makes me think this is just a tricky marketing ploy. Seems to me like this is a fancy way of saying if you pluck in different places on the string you get different sounds- that happens with any string. Until I play these strings, I can't say they seem like anything special.

 

Ellen

[12ax7]

He's actually right, strings do have harmonics and badly made srings will preferentially take up one harmonic over another. A string can be approximated as a chain of weights joined together by springs. Imagine one weight much bigger than the rest, simulating an uneven mass/length on the string, that's going to affect the vibration of the chain. Similarly a particularly strong spring in the chain will also affect the way the chain vibrates. What he doesn't say is that a string manufacturer would have to be pretty inept to make a string that bad. It's just ad-speak. He's basically saying "my quality control is awesome" with badly written techno-babble.

[whit townsend]

Sounds like the Denny Z of string marketers to me.

[Terry Allan Hall]

He's actually right, strings do have harmonics and badly made srings will preferentially take up one harmonic over another. A string can be approximated as a chain of weights joined together by springs. Imagine one weight much bigger than the rest, simulating an uneven mass/length on the string, that's going to affect the vibration of the chain. Similarly a particularly strong spring in the chain will also affect the way the chain vibrates. What he doesn't say is that a string manufacturer would have to be pretty inept to make a string that bad. It's just ad-speak. He's basically saying "my quality control is awesome" with badly written techno-babble .

 

Spot on...spot on!

[NeverSayDai]

So far I make that:

 

7 votes for BS

0 votes for pure gold

 

I think we all agree that Mr Carlos needs a new copywriter! (of course they may be good strings, but the press release isn't great).

 

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Just developing the thoughts a bit further - I will have to sit down with a good book and think a bit about the physics. I feel that you may not be quite right Freeman, I think that any shortening/lengthening of the string disappears very quickly and the vibration in the string remains transverse. Any vibration passed into the saddle should be parallel to the vibrations in teh string, or in the plane of the saddle. There would not be any rotation of the saddle "pulling and pushing the saddle forwards and backwards".

 

If I am right then (to first approximation) the vibrating string is very little affected by conditions at its anchor - i.e. plastic/ebony/brass pins should make little difference (except the differing masses may colour the sound slightly). Similarly the "no bridge pin" bridge doesn't suffer the disadvantages that were suggested in a previous thread.

 

Any recommendations for good books/websites on the physics of the guitar?

[Freeman Keller]

 

Any recommendations for good books/websites on the physics of the guitar?

 

 

The whole physics of guitars, strings, and similar things make great topics for thesis by guitar playing physics majors - I've seen all kinds of analysis of vibrating strings, finite element models of the top plates of guitars, and very high level math trying to explain just how these little wooden boxes work. I am sure that Googling "guitar string vibration" or something like that would lead to many of these that have been published on line.

 

I hang around the MIMF a lot - there are some wonderful discussions about all kinds of theorectial topics

http://www.mimf.com/

 

And many great luthiers post information about the ways they do things, here is just one

http://www.alcarruthluthier.com/Acoustics.htm

 

However two in my library are mostly directed to the builder - Cumpiano's "Guitarmaking - Tradition and Technology" discusses the effects of bracing, different woods and a lot of other factors from the luthier's standpoint, and Roger Siminoff's "The Art of Tap Tuning" has a wonderful introductory section on the physical of many different stringed instruments (fixed and floating bridge). It was from Siminoff that I got the idea of the fixed bridge rocking the top - in fact he says "This soundboard is driven almost entirely by longitudian vibrations pulling at (and releasing) the bridge, resulting in the bridge and soundboard being torqued or twisted back and forth on the bridge's centerline axis". He goes on to describe how a floating bridge actually does vibrate up and down (which makes sense the way it is anchored) and he has a brief analysis of the node in a vibrating string.

 

Ovbviously this one chapter in a book (and dvd) designed to teach a luthier how to voice a top is probably not the best or most economical way to study the physics of the guitar top - just happens to be what I have in front of me.