Vibration down through the legs question

George Kimery · From: Limestone, TN, USA

Quite a while back, somebody had mentioned that Jay Dee Manness could tell if a PP had "that" sound by gripping one of the steel legs and strumming the guitar. Does anybody know if you want to feel vibration or do you not want to feel vibration or somewhere in between? Some vibration, but not too much, etc. If loosing up the screws underneath that hold the guitar together is supposed ot get the right sound, assuming that you get the screws torqued just right, then I would think that there would be less vibration going into the legs due to the looser screws.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

I think the jury is still out on this one, as I've heard conflicting opinions from various pro players. One says you want vibe in the legs, another says this just channels the sustain into the floor. You may be able to make some generalizations about sound with a test as simple as this, but there's so many other factors involved that judging an instrument's sound in this way leaves much to be desired, IMHO. I've noticed that most S10's seem to have more leg vibration than D10's, but I've heard good and bad in both configurations.

I relegate this with kicking tires and slamming doors on a car as a way of judging it's merit. Yeah, it tells you something, but not enough to make any decision about real build or performance quality.

David Doggett · Posted 15 Aug 2008 11:05 am

In order for the strings to have maximum sustain, the changer and nut must be solidly attached to a hard, rigid body. Loose changer or nut connections, or a soft body, absorb vibrational energy from the strings and decrease sustain. And that lost energy will not be audible or felt anywhere. It's just damped out like with a shock absorber. So if you can feel the vibrations in the body, that means the connections are solid, and the body is hard and rigid. If the legs are attached solidly to the body, you should also be able to feel vibrations there.

I don't think those vibrations you feel are contributing anything to the sound. In fact they are some lost energy from the strings. But they are an indication that the changer and nut connections are solid, and that the body is hard and rigid. I suspect you could put shock absorbers between the legs and body to block the vibrations into the legs, and it would have little effect on what's happening with the strings; but it would keep the legs from indicating anything.

There are rubber tips between the legs and the floor. Do those affect anything? Does your steel sound different with or without those tips? What about if you play on a hardwood floor or carpet? I suspect there is too little vibrational energy going through the legs to matter for that sort of stuff.

On the other hand, as long as everything is tightly connected, hard, and rigid, possibly the extra weight of the body and even the legs provides a more stable platform to keep as much of the vibrational energy in the strings as possible.

The resonance of the body is a tricky question. A solid body guitar has much more sustain than an acoustic guitar with a flexible top. The acoustic guitar passes string vibrational energy to the guitar top which vibrates and itself creates sound, just like a speaker cone. In the process, sustain is traded off for volume. The solid body guitar absorbs less energy from the strings, so sustain is maximized, but there is so little volume it has to be amplified electrically. Many people think of the acoustic situation and think vibrational resonance in the solid body contributes to the sustain and volume of an electric instrument. But really, what you feel in the body is lost from the strings, and not picked up by the magnetic pickup, which only responds to metal vibrations (unless the pickup is microphonic - not considered a good thing). Nevertheless, it is a small amount of energy lost in the body, and indicates that the bridge and nut are solidly connected and not absorbing much energy.

If the body is overly soft, it will absorb lots of energy, and you wont feel that in body vibrations. Imagine if you made the body out of soft clay. That kind of poor body material gives rise to the idea that the body vibrations contribute greatly to sustain and volume in electric instruments. I don't think they do. Body vibration you can feel just indicates the bridge and nut connections are solid, and the body is sufficiently hard and rigid. However, the amount and frequency of vibrations absorbed by the body would certainly seem to influence the frequency response and timbre of the instrument to give a darker or brighter tone.

Caveat emptor: I'm no expert, and really don't know what the hell I'm talking about. But it seems to make some sense.

Larry Bell · From: Englewood, Florida

I'll go at it from the other way 'round == the empirical.

I've owned many guitars and many brands through the years and my observation is that I COULD FEEL VIBRATION IN THE LEGS OF GUITARS THAT SOUNDED GOOD (to my ears) AND NO VIBRATION IN ONES THAT DIDN'T.

No idea why or how or how much but try it out on an Emmons or Sho-Bud. Every one I've ever owned transmitted vibration through the legs just by softly strumming across the strings with the guitar not plugged in.

All three of my current guitars are 'leg shakers'.

Very Happy

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C Dixon · From: Duluth, GA USA

Well,

About 11 yrs ago, Ron Lashley Sr told me that the neck of an Emmons was "tuned". When I asked him to tell me what he meant by that, he looked at me with that typical little grin, as if to say, "I ain gunna tell ya!". Then he smiled and we changed the subject.

Many years later, I seemed to recall that Bobbe Seymour said, that Ron had showed him something pertaining to an Emmons that did NOT have "that sound" and one that did. Again, If I remember the story correctly, Ron put his hands on the legs and then did something as a result, whereupon "That sound" was there. What he did, I do NOT recall.

Then I have heard Bobbe say many times, that he does check them using this procedure. And that the neck screws DO play a role in the sound. Again, If I remember it, they can't be tight. Which to me would be going in the other way, but then what do I know? Whoa!

My Emmons '69 did NOT have "that sound". I would give ANY thing to have that baby sitting in front of me now, just to experiment with what a number of notables like Ron Sr and Bobbe have said. But I don't. So I really do NOT know.

For whatever it's worth.

carl
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Richard Damron · From: Gallatin, Tennessee, USA (deceased)

David Doggett -

A little food for thought attendent to your post above.

If we were to study the modes of vibration in a steel string of whatever alloy (done many times) we might first stretch it between two knife edges whose supports had a mass many, many times that of the string. Further, the support structure should not have any acoustic resonances within the range of freqencies of interest.

Why knife edges? As a guitar string vibrates, it precesses about its' longitudinal axis. As it precesses, the string will scrape against its' supporting structure thus reducing the sustain of the string through friction. A knife edge presents a very small point contact. Admittedly, this is somewhat miniscule but, nonetheless, a fact. It then begs the question as to what degree the radius of the changer and/or nut has on the "natural" sustain of the string. Intuition seems to say that the greater the radius, the greater the "interference" thus a greater reduction in sustain. The laboratory apparatus seems to support that notion. Who actually knows? I suspect no one.

As to the mass of the laboratory support structure. It should not, ideally, contribute either positively or negatively to the vibration of the string - either through damping or resonances. Which brings us to the effect that a cabinet, neck, changer etc., etc., has upon sustain and that abominable word "tone". Yes, vibrations felt upon the cabinet face are indicative of losses within the material. But, how much loss? Does the energy resonating within the boundaries of the cabinet contribute positively or negatively through the nut or changer to the string? Most certainly a neck affixed to the basic cabinet will alter the acoustic properties of the assembly in toto. Surely, there must be some frequency dependence to this acoustic "feedback". Perhaps a critical component in the production of tone? Who knows? Once again, I suspect no one.

This brief discussion of mine only alludes to the complexity within the acoustic nature of the beast and is the foundation for my repeated claims that, until the research is done - in a laboratory environment - the elements affecting sustain and tone are total unknowns and any claims made are nothing but conjecture. Empirical observations may have some validity but are subject to the burning question: - "Why?"

Your post shows intuition and an inquisitive mind therefore I am not casting aspersions upon your reasonable thinking. Just adding some food for thought to that already expressed.

Respectfully,

Richard

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