Neck: Density, Stiffness & Contribution to Tone

[Viking]

Question for my guitar building brethren, not that I actually count myself amongst you yet.

I was surfing the LMI website the other day, cause lets face it, there are few things cooler than dreaming about the wood for your next guitar, when I read something about a neck made of EIR here. They said, in reference to using EIR for the neck of a guitar, "Those who have been able to get pieces large enough for necks have reported a dramatic contribution to the tone of the instrument."

The question I have... is why. I think I understand it. If we look at the guitar as a system that manages kinetic energy(string vibration), then we want the maximum amount of that energy feeding into the top, not the neck. A vibrating neck doesn't produce much sound. So if we make the neck stiffer and heavier, it should more readily act as an anchor for the strings, and resist vibrating. If it resists vibrating, then it is leaving whatever amount of energy it would have been consuming to vibrate the top.

One source I read stated that Mahogany has a density of @ 650KG per cubic meter, maple being roughly the same, while rosewood has a density of @ 900KG per cubic meter, making it almost 50% more dense than mahogany. Is this why an EIR neck would result in a better sounding instrument?

So first part of the question. Is my thinking accurate? That the density of the neck is a major factor in how much of the kinetic energy is absorbed by the neck's end of the system? And further that increasing the density can/should result in more of the energy being available for tone production? And assuming the species of wood used has the structural chops to withstand string tension without deforming for the long term, will a heavier, denser neck result in a better sounding instrument?

Second part of the question. Can some of these qualities be artificially imposed on the neck's structure? I've heard of necks being made with carbon fiber reinforcement in addition to the standard truss rod. LMI sells hollow carbon fiber tubing for that purpose. But that seems like it would lower the total density/weight of the neck. So while they are good for the structural integrity of the neck, they wouldn't do much for it's weight. Instead of using a hollow carbon fiber rod, could we use 2 thin steel rods for additional reinforcement? For the dual purpose of raising the stiffness of the neck and raising it's total weight? Something like this seems like it would work.

Thoughts?

[Ned Milburn]

The string vibrates from both ends. So, it is theoretically sending a similar amount of energy into both the neck and into the top. The neck, as you point out, doesn't vibrate much and hence won't send much of this energy to the air as what we refer to as sound.

On my classical guitars, I laminate a 3mm ebony strip into the neck in the belief (hope?) that it will increase sustain.

A "dramatic contribution to tone" sounds to me to be an ambiguous and perhaps meaningless statement. HOW does it contribute to the tone?? More sustain? More volume? More highs? More lows?? More upper partials (harmonics)?? More fundamental??

I have no doubt that an EI Rosewood neck would make a difference to the tone, but if it were such a universal improvement, guitar builders and performers would be aiming for this more often, and the difference in balance would be accepted since there would be a greater benefit in tone.

At lumber supply shops, rosewood is often (usually??) supplied in 1 inch boards, plenty thick for a neck.

The ideal neck, IMHO, is one that is stiff enough to avoid absorbing and slowing the vibration of the strings. Density is likely a factor, but perhaps not so much as stiffness.

Your thoughts seem to be on the right track. If you ever decide to build a neck with EI rosewood, build 2 guitars as exactly similar as possible (same top, side, and brace woods with same thicknesses) and then report back to us on the differences in tone and response.

Another thing to remember about necks is that dimensional stability is extremely important to ensure consistent unchanging action and hence playability. This is one reason why mahogany is such a standard choice. A website called "The wood database" (google it, it will show up right away) has information on different wood species' average properties. Compare the dimensional stability (expansion/contraction along and against the grain) of rosewood, mahogany, and other woods.

[arie]

Originally Posted by Viking

Second part of the question. Can some of these qualities be artificially imposed on the neck's structure? I've heard of necks being made with carbon fiber reinforcement in addition to the standard truss rod. LMI sells hollow carbon fiber tubing for that purpose. But that seems like it would lower the total density/weight of the neck. So while they are good for the structural integrity of the neck, they wouldn't do much for it's weight. Instead of using a hollow carbon fiber rod, could we use 2 thin steel rods for additional reinforcement? For the dual purpose of raising the stiffness of the neck and raising it's total weight? Something like this seems like it would work.

Thoughts?

random thoughts:

-imo; rigidity/stiffness is what i would be after here, not density.

-too much density=more effort needed to drive energy through it. or the more mass you have the more work is needed to overcome inertia. (i think)

-the tool steel rod will flex much more then the cf rods will and will weigh more.

-you might want to consider the cf strips they sell. they offer superior directional rigidty vs. the tubing. sometimes i think about putting 2 strips in a neck 90 deg from each other to increase stiffness in two planes. -someday...

-on the other hand, too much cf in the neck will make adjusting the truss rod a real effort.

page 20 of john greven's 2011 gal discussion might shed some light:
http://www.grevenguitars.com/pdfs/VoicingtheGuitar.pdf

what do i know? i'm pretty much an intuitive fringe builder. (i think)

[murrmac123]

Ned and arie's posts pretty well sum it up.

I would just add my own experience of the contribution of the neck to tone (which doesn't really have anything to do with the OP's question, but I feel it may be relevant nonetheless).

Back in the mid 90's I owned a Lakewood dreadnought, maple back and sides, mahogany neck, which was a wonderful sounding instrument, but I just couldn't come to terms with the neck profile which was just too ..."semicircular" ... for my tastes.

So, I decided I would reshape it, which I did, with a card scraper.

Now, the first thing I did prior to reshaping was to remove all the lacquer from the back of the neck, with the scraper.

The guitar was actually strung up to pitch while I did this, and on an impulse I decided to play it with the neck lacquer removed ...and it was a WOW moment ..I simply could not believe the improvement in volume that the removal of the lacquer had accomplished ( and it was a loud instrument already ).

So that was an eye opener for me ...let there be no doubt that the neck plays a major part in tone production.

[redir]

I think it makes a difference though I cannot quantify it. I won't build a heavy neck on an acoustic guitar, especially classical, but on electric guitars I've used maple and rosewood and it seems to make a difference. If you play the guitars acoustically they just seem different. Probably nothing noticeable though.

Now, where did I read that study that shows CF bars are not really all that effective?

[Alan Carruth]

I just posted a long reply to essentially the same question on the 'General' section of this site. I'll only append here that the use of a fog horn in a Beethoven symphony would be 'remarkable', and so is Yo Yo Ma's playing of the Bach 'cello suites: it's a word with a range of meanings.

[arie]

you know, fwiw i think that lmii's description of cf as "graphite" could be missunderstood:

http://www.lmii.com/products/mostly-...reinforcements

wikipedia:
http://en.wikipedia.org/wiki/Carbon_(fiber)

anybody who has machined graphite electrodes knows that pure graphite is a different animal.

haven't had a chance to play with lmii's product. last i machined cf it had fibers poking out of it that imbedded in your skin, the resin smelled really bad, and cutting tools got dull within minutes (we used a router mounted to a 5 axis gantry mill). has this been the experience with lmii's stuff?

[John Arnold]

Graphite was the term used for carbon fiber when it first hit the market. There were 'graphite' tennis racquets, golf club shafts, and even a few bicycles.

-too much density=more effort needed to drive energy through it. or the more mass you have the more work is needed to overcome inertia. (i think)

The whole point of a stiffer, denser neck is that you don't want the neck to vibrate.

-the tool steel rod will flex much more then the cf rods will and will weigh more.

For equal volume, carbon fiber/epoxy is not as stiff as steel. It is much stiffer than steel for its weight, however.
The way to get a higher stiffness to weight ratio is to make the beam from a lighter material and make it taller....something that cannot be done when the depth of the neck is limited.

IMHO, a solid rosewood neck is too heavy for an acoustic guitar, at least one that is not overbuilt.

[printer2]

Mass is not the only answer, otherwise a hollow neck filled with sand would be acceptable. For some reason I get the feeling it would not. Now a glass neck? Shame I just threw out a bunch of thick glass windows. Kind of touchy pounding in the frets though.

[Viking]

Originally Posted by John Arnold

The whole point of a stiffer, denser neck is that you don't want the neck to vibrate.

Yeah, that's what I'm shooting for.

Often, when I think of these things, I tend to go to an extreme in my mind to illustrate a point. Imagine that one end of the strings of a guitar are attached to a 1000LB concrete block, the other to a lightly built acoustic guitar top. Forget for a moment the practical aspects of building such a thing. How much of the energy of the vibrating string is spent at the concrete block end of things? Pretty much none, right? Almost all of it would be spent on the soundboard's end of the string. That's what I'm referring to here. A more massive, more dense neck should mean more of the energy is available at the point in the system where it will do the most good.

There would obviously be an upper limit to how useful this could become without encroaching on the playability of the instrument. If the neck is too heavy the balance of the guitar is lost.

Originally Posted by John Arnold

IMHO, a solid rosewood neck is too heavy for an acoustic guitar, at least one that is not overbuilt.

Part of the way my thinking is evolving on some of these issues, is that the term "overbuilt" is really only applicable to certain aspects of the system. Those aspects that are SUPPOSED to vibrate should be made as lightly as possible(top, back, bracing). Those aspects of the system that are not supposed to vibrate can be made heavier and that will in fact allow the energy budget to be spent in those places where it will produce a maximum of acoustic return.

This would be why those like Somogyi(at least, in the way that I am thinking) use a heavy upper transverse brace firmly anchored to the sides, double sides, and the L shaped inside heel block. Thick, heavy structures to ensure the structural integrity of the instrument, AND, to minimize the amount of energy lost to those parts of the system, leaving that energy in the places where it will do the most good.

Is this a valid way to view the system?

I'm certainly noticing that when you ask a question of 10 guitar makers, you're going to get 15 different answers. Makes me believe that all these different schools of thought represent local minima in this complex system of variables. And further, that a global minima may not actually even exist.

[charles Tauber]

Originally Posted by Viking

A more massive, more dense neck should mean more of the energy is available at the point in the system where it will do the most good....If the neck is too heavy the balance of the guitar is lost.

This was exactly Kasha's thinking back in the 1960's and what Schneider implemented. He went so far as to use a steel H between neck and body, embeded "inertial weights" in the head under the head veneer and then balanced the whole thing by adding counterweights in the end block.

Is this a valid way to view the system?

"In theory, theory and practice are the same. In practice, they are not."

In my opinion/experience, no. The lighter the better.

I'm certainly noticing that when you ask a question of 10 guitar makers, you're going to get 15 different answers. Makes me believe that all these different schools of thought represent local minima in this complex system of variables. And further, that a global minima may not actually even exist.

As my fluid mechanics teacher used to say, "An art is a science with too many variables." With that many variables people assign cause and effect as it suits them, regardless of the absence of proof of correlation.

[rick-slo]

Not much effect on tone, a bit more on sustain.

Neck vibrations are to a larger extent attenuated by the time you are up the neck towards the body so what does go on is mostly vibration feedback from the headstock and nearby fretboard areas back to the strings. The effect is larger the lower the frequency of the note. The greater amount the neck absorbs the string energy the greater loss in some of the guitar's warmth and sustain. However this amounts to a small part of what gives the guitar its overall tone, so I would not expect it to be very noticeable.

[Jim.S]

Originally Posted by Viking

Part of the way my thinking is evolving on some of these issues, is that the term "overbuilt" is really only applicable to certain aspects of the system. Those aspects that are SUPPOSED to vibrate should be made as lightly as possible(top, back, bracing). Those aspects of the system that are not supposed to vibrate can be made heavier and that will in fact allow the energy budget to be spent in those places where it will produce a maximum of acoustic return.

This would be why those like Somogyi(at least, in the way that I am thinking) use a heavy upper transverse brace firmly anchored to the sides, double sides, and the L shaped inside heel block. Thick, heavy structures to ensure the structural integrity of the instrument, AND, to minimize the amount of energy lost to those parts of the system, leaving that energy in the places where it will do the most good.

Is this a valid way to view the system?

I agree that this is a valid way to view the system (though the neck is not something I see a need to make massively heavy), depending on what you want to achieve with your instrument. If you want to achieve a more efficient guitar then it can be demonstrated that adding side mass will increase efficiency. This has been demonstrated before and follows your line of thinking. If you take a guitar (one with average side weight to begin with) then using the Chladni method find the node of the monopole mode of vibration of your top, you will see that it is somewhat inboard, away from the ribs. If you then add side mass, say 0.5Lbs to either side of the lower bout then Chladni test it again you will notice two things firstly that the frequency of the monopole mode will be lowered and secondly that the node of that mode will have moved outboard closer to the ribs allowing a larger area of the sound board to move making it more efficient.

Jim

P.S. If you are interested in this Viking I will PM you a title of a book that you will find very helpful. I would just put it here but not sure what I may be allowed to advertise here, not that I am in anyway associated with financial gain from the sale of this book.

[printer2]

A guitar neck is a column that we do not want to bend (oscillate back and forth), we want the guitar top to bend. So how do you get a column to resist bending? Make it stiff.

Little car and a big car meet on the road in unfortunate circumstances. The little car bounces off while the big car gets changes vector. Next little car and a semi, little car, you guessed it, semi rolls to a stop. Next a train and a small car, the conductor slows down to see what that was.

Looking at the energy of the string and the neck, well there is not much in the way of impact. The mass of the string is much smaller than the mass of the neck. You could set up a jig the shape of the back of the neck on a heavy oak workbench and clamp the neck down allowing space for a couple remaining strings that you can pluck. Will the the tone change much now that you have a couple hundred pounds of mass hanging of the neck? Probably not.

But I am just guessing here, and that is not good enough for me. I'll be right back.

I could not hear much difference, hard to say given the nature of the test though. I took a guitar I made with a poplar neck that is very resonant, can feel the neck vibrate when you pluck a string. Took a longer radius block and clamped the neck with quick release clamps to a 100+ lb thick glass top coffee table. Now plucking the string I feel absolutely no vibration off the neck.

Try to be consistent in plucking the open string and listen carefully, pop the two clamps off and pluck again. No change that stands out, mind you I am only using one open string and not fretting it along the neck so can't say it is the same everywhere. But given that the neck used to vibrate and clamped it did not and I did not hear a change (but I must admit I do not have golden ears).

As my fluid mechanics teacher used to say, "An art is a science with too many variables." With that many variables people assign cause and effect as it suits them, regardless of the absence of proof of correlation.

Maybe with a better guitar a change may be more apparent. Maybe even change the bridge on this one may help (I want to do it and one day will get to it. Hey, I taught fluid mechanics also. ).

[arie]

Originally Posted by John Arnold

"Graphite was the term used for carbon fiber when it first hit the market. There were 'graphite' tennis racquets, golf club shafts, and even a few bicycles."


"For equal volume, carbon fiber/epoxy is not as stiff as steel. It is much stiffer than steel for its weight, however.
The way to get a higher stiffness to weight ratio is to make the beam from a lighter material and make it taller....something that cannot be done when the depth of the neck is limited."

i know. it's rather silly though, graphite has no fibers in it. i worked in a place where the owner of the company put carbon black in the the hopper of his molding machines to inject "carbon fiber" into the side plates of his fishing reels. not "graphite", not "carbon fiber", -just soot. pure marketing bs.

scientifically true, but given the constraints presented by the OP, his water hardening tool steel rod will flex more and weigh more the a "carbon fiber" tube. if he wants metal, he would be better served by using heavy wall tube rather then solid rod. at least then he can benefit from the increased surface tension of both the inner and outer surfaces combined and lose some weight.