Comments on: Physics, guitars and pitch harmonics

By: David Farrell

David Farrell — Mon, 09 Jan 2012 16:57:32 +0000

One more thing, there is a slight difference between the oscilloscope single traces formed when this is placed into a feedback – amp and the gain is dialed up – amp is close to the guitar, so sonic vibration excites the strings. In the case of plucking a single string harmonic, with a single trace shown, I found that the other strings try to find this freqency or creep in other modes, so you have to damp them with your hand. This tells me that even though I plucked a string, and that is dominant, the nearby response from the unplucked strings factors into what you are hearing. Normally nobody would believe this. This concept does not work as well with chords making a single trace , which is very interesting. The strings can excite each other and it is more robust as far as holding onto the single trace pattern on the oscilloscope. There is less creep . This is intuitive as a guitarist. Lots of fun to see these. My teenagers love it and show it to pals.

By: David Farrell

David Farrell — Mon, 09 Jan 2012 16:46:01 +0000

Also, a pal of mine, who is an aerospace engineer like myself, suggested using a FFT to identify these freqencies and to verify that they add together to form the shapes shown on the oscilloscope as only a single trace. In other words these odd shapes are formed by adding all these frequencies and whatever it is that causes these to appear to rotate, like a crown spinning on the vertical axis, can be explained . I would not mind anyones input on this, I dont think it will explain it myself, but it may help. It is obviously a non linear effect and the energy is bleeding out – either off the ends of the strings or due to air friction as well. When feedback happens the same shape can be held , but you can see the tendancy to have frequency creep as the deflections get smaller. The amplitude does affect the tonal response.

By: David Farrell

David Farrell — Mon, 09 Jan 2012 16:37:38 +0000

I have attached an oscilloscope to my guitar. Realizing that it will show all the modes for any string plucked, I did not expect to see any clear single trace. What I found is that several chords and some harmonics can produce a single trace, normally you get several modes on top of each other. Some of these special single trace shapes look like a crown that is slowly rotating, the frequency of the rotation appears to match the rate at which the guitar is loosing amplitude. I then hooked up feedback to keep it going and this is totally cool. Suggest you try this and come up with a theory on why the rotation rate slightly varies between these traces. Energy methods may apply. The math gets complex. I think I am looking at a coupling term such as in the D matrix since spring axial stiffness dominates normally. Bending is usually ignored in the strings.

By: skullsinthestars

skullsinthestars — Thu, 17 Mar 2011 00:05:21 +0000

I’m glad you liked the article! I don’t know the specific model of my guitar, but it is an Ibanez.

By: NM2433

NM2433 — Wed, 16 Mar 2011 01:14:49 +0000

Awesome article!
I’ve been playing for over 2 years and am doing a project on exactly this sort of thing: the physics of guitars.
One question: What is the model or make of your guitar? It’s really slick looking and I can’t find it anywhere. Thanks!

By: skullsinthestars

skullsinthestars — Fri, 14 May 2010 19:28:22 +0000

I don’t know of any articles detailing the phenomenon; that is, in large part, why I was motivated to write this post!

By: H. R. Park

H. R. Park — Thu, 13 May 2010 05:14:28 +0000

Your article is strongly impressed on me.
I’m wondering if there are some physics papers or books related to pinch harmonics of guitar playing.

By: Kayla

Kayla — Mon, 19 Oct 2009 14:16:29 +0000

I score boyss everyday cause i play the guitarrr ;P

By: skullsinthestars

skullsinthestars — Mon, 14 Sep 2009 02:42:29 +0000

Thanks for the comment! I certainly think that physics rocks.

By: JB8544

JB8544 — Sun, 13 Sep 2009 15:16:05 +0000

This is really cool. I am a student that just started taking physics and I’m also a guitarist. Physics rocks!