Official Luthiers Forum!

Re. this neck system:

1) the CF is about 1/8" up into the fingerboard which becomes an incredibly strong and stiff structural member. I can put one of these on blocks (at each end of the fingerboard) on the floor and stand on it with less deflection than if I did this with an entire Tele neck.

2) No, I superglue the CF rods into the fingerboard dadoes. Then it's WEST or Franklin polyurethane glue.

3) Yes, it's how we do all the acoustics now. Works great.

4) We're fretting before we glue the fingerboard to the neck, and that's one of the beauties of the whole thing.

We're still evolving this whole system, but it has great promise.   As we move into more and more use of our CNC machine, as we tool the Model 1, acoustic, and some other necks, we'll perfect this whole thing.   Aside from resulting in what I think will be a superior neck, the other factor is time.   I think we'll be able to cut a good hour and a half to two hours out of build time by having near-perfect fretted fingerboards as a subassembly. At 20 guitars and basses made like this a month, that's saving nearly a week of one worker's labor to achieve a superior result. When we can move onto our bar fret idea...whether they are ceramic or nickel silver, the time savings will be another couple of hours or so per instrument.    

Hi Rick
I don't really want to deviate the subject here from damping to neck mechanics but I see from your website that you use an adjustable neck and you say that you use two 1/8"x1/2" CF rods. When I have use CF in my necks, I find that they are much harder to adjust. Perhaps the rods I was using then were bigger (I don't remember) but you can apparently adjust your necks with these CF rods in or is that a different design you are working on. I use two 3/16"x1/4" CF rods in my ladder guitars but they are non adjustable necks in trying to stay true to these old ladder guitars but I am thinking of adding even more stiffness to them and am intrigued by your method of extending the CF into the fingerboard. It would be extremely handy to be able to stiffen the fingerboard and do frets before installing the fingerboard.

I sent this as a PM to Rick but meant really meant too post it here.

_________________
Tickle your guitar daily, and it'll tickle you back.

Thanks for sharing this Rick. I plan to do some trials using your method.

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com

I am really pleased with the carbon-rods installed in my neck of my second guitar build. Such a stable system, and worth the extra $.

I know it's not a new concept, but from where I'm standing, the novelty of this discovery has not yet worn off. My deep gratitude is to those who discovered this design and being so generous in sharing this information.

Sam, an interesting one for me was restoring a really beat up Dyer (Larson Bros.) harp guitar about 15 years ago. It needed a new fingerboard, among other issues, and when the 'board was off I decided that we'd put a couple of CF rods into the neck. It made a wonderful difference in the volume, tonal evenness, and sustain of that guitar.

sbrunker wrote:
"If I used a heavy, dense material for the nut, wouldn't the damping at the nut end result in re-directing energy back down the string to the saddle? "

That's not damping, it's impedance. It's a whole other subject, but it feeds into the damping discussion. Basically, impedance is a measure of how hard it is to move something at a particular frequency. It's determined in part by the damping, but mass and stiffness also come in.

When you have two things with matched impedance all of the energy can flow from one to the other. That's one reason you try to impedance match speakers and amps; it's more efficient, you get better frequency response, and you're less likely to blow your amp.

Strings have pretty low impedance. A banjo head comes about as close as anything to matching the string impedance, and you know how much sustain you get from those. Acoustic guitar tops/bridges generally have higher impedance than the strings at all frequencies, and that keeps the energy from 'leaking' out of the string too fast. The impedance of the guitar top is lowest at its resonant frequenies, and that's one reason you can get 'wolf' notes and feedback at those pitches: the transfer of energy between the string and top is highest. An electric with a good heavy bridge screwed down to a nice solid body gives a big impedance mismatch; lots of sustain and not much acoustic volume.

A heavy brass nut also gives a large impedance mismatch at that end of the string, but brass in itself has very low damping. It keeps the energy in the string not because of the damping, but because of the mass and stiffness.

Rick's super reinforced neck also keeps the energy in the strings because of it's stiffness. The relatively small force that the string can apply to bend it doesn't do much, so the nut end of the string stays put and reflects the energy back down the string. The Parker 'Fly' guitar got decent sustain out of a 2-1/2# instrument because the CF 'skin' made it so stiff. I suspect this also had the benefit of shifting the resonant pitches up well beyond the fundamentals of the most of the notes you'd play.

This is entirely anectodal, but I have been keen on using softwoods in electric guitar necks for awhile now.  Modulus did this awhile back using a combination of cedar and CFRP, but some of the softwoods are actually stiff enough to work on their own. 

I'm currently refinishing a small-bodied electric (akin to an Ernie Ball Axis) with a sitka body, and a douglas fir top and neck.  The old-growth douglas fir is very stiff and stable.  No carbon.  Just a simple truss rod.  The wood is stiffer and more stable than maple while being less dense than mahogany.  The instrument has an amazing acoustic-like richness lacking in most solidbody guitars.  The biggest concern is it has to be treated carefully to avoid dings.  Doug fir can also be brittle.

My recent purchase from Dave Wendler likewise has a douglas fir neck.  He laminated it from three pieces, and the instrument has a a 26.4" scale, but the outcome is similar to my own project guitar.  The spectral richness amazing, and the neck seems very stable.  No carbon.  Just a simple truss rod.

I'm now thinking about using hollow square-bore CFRP tubing in place of the truss rod.

Thanks for the interesting discussion.  FWIW, temperature and frequency-dependent damping is precisely defined by the loss tangent, tan(delta), where delta is the phase lag between an applied force and the reactive response (force) directed back by the material under cyclic load.  It is further defined as the ratio of the "storage modulus," E', which you can think of as the linear elastic stiffness of the material, to the "loss modulus," E'', which can be thought of as the viscous (liquid-like) loss of the material.  For woods, it generally holds that the loss tangent decreases as the speed of sound within the material increases, and that quantity is proportional to the transverse stiffness divided by the square of the wood's density.  Therefore, lighter and stiffer woods tend to dampen less. 

As Al has correctly pointed out, these intrinsic properties have nothing to do with the overall mass, or inertia, of the tested body.  That is an extrinsic property that contributes to impedance but not to a loss of acoustic conversion efficiency.  However, extrinsic properties like neck geometry and mass contribute strongly the instrument's fundamental resonance modes.

-Ben

Hold on a minute... are some of you using expanding truss rods to get more relief after installing CFRP bars?!

-Ben

Ben:
Interesting. Haines, in his program of wood testing, found that damping in most woods was lowest at low frequencies, rose slowly as the frequence went up to about 2kHz, and then rose faster after that. The exceptionin his tests was Sitka spruce, which had higher damping at low frequencies, but the danmping factor went down as the frequency went up until, at 2kHz, is was about like that of other softwoods, and then it rose as the other woods did. Nobody knows why there is that 'dogleg' in the plot, or even whether it might simply be an artifact of his measurement technique.

"Therefore, lighter and stiffer woods tend to dampen less. "

I'm not sure that damping and density are all that strongly related, at least across species. Western Red cedar tends to be less dense than most of the spruces, and Redwood more dense, but both usually have lower damping than the 'average' spruce. Doug fir, which is often as dense and stiff as (if not stiffer than) many hardwods, also has low damping usually. It's interesting that the low damping softwoods also tend to be splitty: suggesting that there is some structural reason (lack of cross-linking?). In the hardwoods, Brazilian Rosewood, Padauk, Osage Orange, Pernambuco, and Black Locust are all dense to very dense woods that have low damping. Maple, mahogany, and so on, tend to have higher damping.

In the end all of the 'tendancies' are just that, of course: you have to measure the individual piece of wood to really know.     

[QUOTE=Alan Carruth]Haines, in his program of wood testing, found that damping in most woods was lowest at low frequencies, rose slowly as the frequence went up to about 2kHz, and then rose faster after that. The exceptionin his tests was Sitka spruce, which had higher damping at low frequencies, but the danmping factor went down as the frequency went up until, at 2kHz, is was about like that of other softwoods, and then it rose as the other woods did. Nobody knows why there is that 'dogleg' in the plot, or even whether it might simply be an artifact of his measurement technique.[/QUOTE]

Thanks for your reply, Alan.  Most of what I know about damping in softwoods comes from some Japanese journal articles from the early '90s.  I will have to dig them up if you would like the references.  I can also send you copies.

IIRC, the flexural testing was done at 1 kHz, and you can see the damping go down as the stiffness per unit density goes up.  I also seem to recall that there were a couple of outliers.  I think the noble firs have particularly low damping.


[QUOTE]I'm not sure that damping and density are all that strongly related, at least across species.[/QUOTE]

You're correct that the density, apart from stiffness, isn't so important.  However, the stiffness per unit density (i.e. specific stiffness) is important.

[QUOTE]Western Red cedar tends to be less dense than most of the spruces, and Redwood more dense, but both usually have lower damping than the 'average' spruce. Doug fir, which is often as dense and stiff as (if not stiffer than) many hardwods, also has low damping usually. It's interesting that the low damping softwoods also tend to be splitty: suggesting that there is some structural reason (lack of cross-linking?).[/QUOTE]

Douglas fir is an exceedingly stiff wood, so even though its density is
higher the specific stiffness is still high.  I think only adirondack
spruce and the noble firs have higher specific stiffnesses than douglas
fir from the pacific northwest.  Doug fir from the drier mountain
regions is a bit different, but it's still good instrument wood.

You are far more knowledgeable than I am about the practical characteristics of these woods.  I am familiar enough with cedar to know that it tends to be more "mellow."  Good redwood is hard to find.  Larry Stamm is the only person I'm aware of that regularly uses douglas fir in acoustic tops, and I haven't played his instruments.  As far as working properties go, sitka spruce is one of the "tougher" woods in terms of split resistance.  This probably goes along with lignin content, but I'm not sure. 

Contrary to intuition, higher crosslinking densities make wood stiffer and more brittle.  Crosslink density goes up - to a point - as wood ages.  In fact, the same Japanese studies I mentioned above were aimed at increasing the acoustic conversion efficiency of "new" softwoods by artificially aging (crosslinking) the cellulose with formaldehyde.

Then there are the mythical microwaving treatments and other thermal treatments (ref. Ruokangas).  These most likely increase crosslinking.


[QUOTE]In the hardwoods, Brazilian Rosewood, Padauk, Osage Orange, Pernambuco, and Black Locust are all dense to very dense woods that have low damping. Maple, mahogany, and so on, tend to have higher damping.[/QUOTE]

The exotics are "low damping" only at lower frequencies, correct?  These are somewhat oily, "rubbery" woods.

[QUOTE]In the end all of the 'tendancies' are just that, of course: you have to measure the individual piece of wood to really know.[/QUOTE]

How true!  It always takes a luthier such as yourself to get the right tap tones at the point of application!

BTW, I forgot to mention that those fir necks of mine both have pau ferro fretboards.

Best wishes,

-Ben

As for necks and their contribution to sound, has anyone here tried subbing out several different necks on the same body?  Seems like that would be particularly easy for those of you building modular, adjustable necks.  I'd be curious to hear about any results from that kind of experiment.

I'm well convinced that the neck is acoustically important but I find it pretty hard to really get a handle on controlling the relationship.  Talk about a lot of variables!  Unless you just go as stiff as you can, how are you going to be consistent?  Unlike with tops and braces, there's not much you can reasonably do to control the variability from one piece of wood to the next.

I built a couple of guitars where I made bodies similar to what I had been doing but added necks made stiffer by cf bars and slightly thicker fret boards.  The result was clearly more power but a sound that was distinctly more brash, less warm.  I'm not saying that's universal but I was pretty sure it was causal for me.

After seeing a guitar whose bass improved drastically with a capo clipped to the peghead, I experimented with adding some mass to my pegheads.  That and then clipping capos to the peghead of lots of guitars gave the impression that the first guitar was an anomoly.  On most guitars, the main effect of adding mass to the peghead is making a distinctly neck-heavy guitar.

People pick up a guitar before they play it.  In so doing, they feel how heavy it is.  If heavy then people tend to develop a negative bias before they even play it.  It's hard to overcome first impressions.  I've been trying to make necks as light as possible and work with everything else for tone.

_________________
http://www.chassonguitars.com

Ben Furman wrote:
"You're correct that the density, apart from stiffness, isn't so important. However, the stiffness per unit density (i.e. specific stiffness) is important."

Hmmm. I've been measuring the main structural properties all my top wood as it comes in for the past few years. One thing I find interesting is that, in a plot of density vs Young's modulus along the grain, all of the 'usual suspects' fall pretty much along the same line. There is far less scatter than I expected. Low density top woods, like Red Cedar and Englemann, can come in around 350 kg/m^3 (sp. g.=.35) and a lengthwise E value of around 9000mPa. Some Red spruce and Sitka samples are up around 500 kg/m^3, and 16,000 mPa. Since the relationship between density and E value is linear the less dense wood will make a lighter top for a given stiffness. Anyway, I'm not sure how this relates to your 'specific stiffness'. I'll have to see if the denser tops at a given stiffness tend to have higher or lower damping, but I fear my sample size is not high enough for firm conclusions.

With all the 'usual' difference, I have a cedar top and a Red spruce top that are within 2% of each other in every measure but damping, with the cedar being much lower in that respect. That's going to make an interesting pair of guitars.

When you install the carbon fiber in the neck, will this prevent the neck from being bendable (when you play?) Bending the neck is an important part of my style, I dont want to give that up. With standard dred mahogany necks I have never had any structual issues bending the neck a bit (ala wa wa bar) to raise the pitch of a cord or note. I cannot do this on classical guitars which really bothers me.

Here are some data from one of the articles I dug up:


The data are from Teruaki Ono and Misato Norimoto, "Study on Young's Modulus and Internal Friction of Wood in Relation to the Evaluation of Wood for Musical Instruments," Japanese Journal of Applied Physics, 22(4), 611-614 (1984).

In the above plot, 1/Q is a measurement of "internal friction," which is equivalent to the loss tangent, measured over the frequency range of 250-700 Hz.  E is the Young's modulus, and the symbol gamma indicates the specific gravity, which is a unitless measure of density.  In general, a lower value of Q resulted in qualitatively more sonorous piano soundboards, and this value tended to decrease in softwoods as the specific elastic modulus of the wood increased.  The differences in specific modulus were correlated with microfibril angle in the secondary wall structure of the wood cells.  Internal friction decreased as the microfibrils became more longitudinally aligned.

I don't know if they still offer this, but the bound LMI catalog used to have specific density measurements listed for a whole host of woods, including most of the hardwoods used by luthiers.

-Ben