Official Luthiers Forum!

I'm currently building a 000 12 fret guitar for a client and he is interested in having a maple neck to compliment the African Blackwood Back and Sides. I have always used mahogany for my guitars with the exception of archtops, which usually use a maple neck. My question is, what are your thoughts when it comes to the necks affect on tone for an acoustic guitar?

Neck materials seem to have a large affect on solid body instruments, but I believe this is because string energy is transferred/absorbed differently in solid body's compared to acoustics. My opinion tends to lean toward the thought that it doesn't have a major contributing factor on acoustics, but I'd like to find out your thoughts.

_________________
Chris Alvarado
www.ChrisAlvaradoLive.com
www.Driftwood-Guitars.com

I won't commit to the tone properties of neck wood. Pretty tough call. But the wood match is something to put some thought into. Mahogany would be nice. Mahogany with black dye might be cool. A 3 piece, high figure Maple neck with a black wood of some sort for the centre lamination could be way cool. Some Maple appointments to balance it out. I just did a Wenge guitar with a Maple neck. I like it a lot. I hope someone else does too.

There's a simple reason why the neck has such an effect on the tone of a solid body guitar: it's the most flexible part. Solid body necks tend to be thinner than those on acoustics, and longer, and they're attached to a slab of solid hardwood. If anything's going to move at an audible frequency, it will be the neck, and in doing so it alters the way the strings work, and what the pickup 'hears'.

So far the only reliable 'neck' effect I've been able to find on acoustic guitars happens when the lowest resonant mode of the whole body/neck system is high enough in pitch to match the 'main air' resonant frequency. When that happens the two can couple. The result, as seen in a spectrum chart, is that the 'main air' peak is lower than it would have been, and split into two peaks with a dip in between, like a dromedary hump. The area under the curve, the 'total available horsepower', can actually be greater than it would be without the coupling. There is also lees chance of a 'wolf' note at the 'air' pitch. In some cases the outcome is a guitar with a particularly 'dark' and full bass sound.

It's not common to see this on steel strings, although it's more likely on 12-fretters; usually the so-called 'neck' mode is down around C and the 'air' mode is closer to G. Classicals, with their larger necks, are more likely to have this happen. Since the headstock moves a lot in this mode of vibration the mass out there is a big factor. Light weight tuners can help a lot. Since the frequency math has to be almosty perfect for the effect to show u, even a small change in headstock mass can make a difference in the sound. Now you know why some people get a big change in the tone when they swap out tuners, and others don't.

How does one excite and measure a neck mode?

I wouldn't think twice about a tone difference but weight has consequences... Maple is generally heavier and can make SS guitars top heavy especially with big sealed tuners, but with an African blackwood back and sides and a 12 fret neck you might have the opposite problem where a heavier neck might actually make a better balanced guitar.

Hold it up by the neck around the first fret, and tap on the end of the headstock.

I agree with James, worry more about weight than tone. And actually, I'm not sure a lively neck is desirable, since it transfers vibrations from the after-length of the string to the box. Particularly irritating when playing hammer-ons up the neck.

Thanks for the food for thought. My main argument against the maple is that it's heavy, but I understand how this might balance the weight with ABW back and sides.

_________________
Chris Alvarado
www.ChrisAlvaradoLive.com
www.Driftwood-Guitars.com

Don't be afraid of a maple neck. It not that much denser than mahogany and much more sustainable.
I feel the neck doesn't add to the tone but it does have the ability to detract from it. Think about it like this, it takes energy to make something vibrate, therefore you would want all potential energy to drive the parts that make sound efficiently (i.e. the top), not parts that are high mass and low surface area ( the neck).

Collings guitars states on their tours that a neck with flexibility can rob vibrations that should go to the top. They put spring steel in their necks to stiffen.

Only concern about a maple neck is that it's harder to carve.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

One thing that I think has a big effect on tone is the fingerboard. I would have never believed it, but I got to check out 2 PRS acoustics of the same body type, built by the same builder from sequential sets of wood (b&s as well as top). Everything was the same except for the fingerboards, and there was a noticeable tonal difference. The one with the ebony fingerboard was much brighter and the one with cocobolo was much darker sounding...

_________________
http://www.PeakeGuitars.com

I've built matched pairs of guitars from the same wood throughout, and had them come out sounding different. Until somebody can demonstrate the ability to make identical ones on demand I'll remain pretty skeptical of that sort of test.

If anybody could build identical guitars, I would wager it would be PRS.

Theoretically, the obvious follow up to what Parser described would be to remove the fretboards and swap them over (should be easy enough if the guitars are identical) and see if the sonic differences interchange. In practice, of course, given the price of PRS acoustics, I doubt it would be feasible.

murrmac wrote:
"If anybody could build identical guitars, I would wager it would be PRS."

Why do you think that? If they're matching the dimensions exactly then I can pretty well guarantee that they're not going to end up with identical' instruments, unless they happen to get two sets of wood that are the same, and even then I doubt it. Given that two pieces of spruce of the same species can have Young's modulus values along the grain that differ by plus or minus 20% and cross grain values that are even more variable, you can't go by the species. I recently cut two WRC tops 'in flitch' from a very uniform wedge of wood, and when I measured the cross grain stiffness one was nearly 20% stiffer then the other. This was from a barely visible difference in ring angle. I very much doubt that any factory is doing quality control that would be up to the task.

I've also built matched guitars from the same exact filch of wood top and back and sides and they sound different. So I agree that is an impossible test to verify. Having said that my experience is the exact same as the OP regarding the effect of tone on the electric guitar. It's always a point of contention in the electric guitar world concerning 'tone' wood for electric guitars and most folks think I'm crazy to say the body has not much to do with it but the neck seems to me to have a lot to do with it. Alan's description is interesting as it offers some logic to the gut feeling I've always had in this matter.

Well, we certainly weren't matching Young's Moduli or anything. They were sequential sets of wood and the builder is a very consistent builder and overall an excellent craftsman. They were as alike as any two guitars could be. I guess we could have done a fingerboard swap if we were that interested.

I think it's OK that they sound different. Different people like different tones. Paul liked the darker sounding cocobolo and we had plenty of good players who liked the brighter ebony one.

As an aside, while we were setting up production for the acoustics I tried to extoll the virtues of FEA but it pretty much fell on deaf ears. I did some preliminary isotropic analyses (they did not want to fork out the $ for the software to do a real orthotropic analysis) that suggested their bracing design (a hybrid x-brace/fan bracing pattern) reduced stresses in the top by about 10% and recommended that they not reduce top thickness any more than would make up this 10%. Paul was big into making the tops as thin as he could at first. Long story short, they made them too thin at first but have thickened them up now. From what I hear, they are making some really nice instruments now.

_________________
http://www.PeakeGuitars.com

I don't think it's 'impossible' t ever make a truly matched pair of guitars, and hope to explore this a bit more at some point. I do think it's going to take a lot of very tight QC. I'm also not entirely sure we know just what's needed to do that; it's possible that some of the things we think of as important are not, and vice versa. Once its been done a few times with tight controls we can start relaxing things a bit to see what matters.

I get very consistent results by tightly controlling material properties of the materials and finish thickness/ bridge mass etc. I do not think identical, or near identical guitars are impossible or even hat difficult if you pay attention to the right things.
I believe that most myths regarding the effect of the neck on tone are a result of observations of factory made instruments. One might think that they must be identical because of the production line process, but that fact that all parts are treated the same pretty much guarantees that the guitars will NOT be identical, as material properties of guitar wood vary by some 25(?)%
all in all, I have not found that the neck has a profound effect on the tone of my instruments as long as the necks are made to be as stiff as they can be.

I get consistent results too, and so do many hand makers. 'Identical'; that's something else...

i guess is should say "close enough"

Actually despite the high quality and artistry of good workmanship by humans, automated systems typically perform the manufacturing process with less variability than human workers. The result is greater control and consistency of product quality especially where mass production is concerned.

In Theory.

So in Theory a company like Taylor would be way better at making two guitars using the same materials sound the same. Like I stated I tried it, even from the exact same boards of wood cut one right after the other, can't get any closer then that, measured all parts to be identical same everything and I got two different guitars. Not like so different that one sounded liek it was made with a cedar top and the other Sitka but still different enough to be able to say for example the whole bolt on vs dove tail neck and tone is BS. IMHO of course.

"In theory there is no difference between theory and practice, but in practice there is"

As has been pointed out, 'the same' materials aren't the same. I have two pieces of spruce, cut from the same length of a board, three inches apart, that are within 10% of each other in density, but one is only half as stiff along the grain. I have two cedar tops cut next to each other from the same plank, and one is 20% stiffer across the grain. If you look at wood within the same species the variation can be much wider, particularly in cross grain stiffness. I have Sitka top stock with similar long-grain stiffness but one piece has a long:cross stiffness ratio of about 8:1, and another 62:1. Long-grain stiffness varies by at least 20% plus or minus from 'average' values within a species, and there's a lot of overlap between species.

If you were manufacturing, say, automobiles, and your supplier told you he could not guarantee the properties of the steel to within 20% of the specified values, you'd be looking for another supplier. It would simply be impossible to make a product that would perform to standard under those circumstances. Guitar manufacturers get away with it because the designs are really good, and the standards are all more or less subjective (not stuff that can be measured like, say, 0-60 in 8.5 seconds, or 35 MPG). The instruments they make all sound different, but the customers are each looking for something 'special' anyway. The result is that every instrument they make is likely to be somebody's 'Holy Grail'. If they can find that person, they've got a happy customer.

Luthiers are more in the position of the auto maker: they have to hit certain performance targets, and so do we (the fact that they're subjective just makes hitting them all that much more interesting). To do that with variable materials you either have to learn how to pick the set of wood that will make the guitar you want to make, or else to vary the dimensions to adapt to the set you have. In practice we usually do some of both. That's not a strategy that can work in mass production. It also works against the sort of 'precision' of fit and finish that the hallmark of mass production. When you have to rely on tool chops rather than a jig to get things right, there's more chance for error. That's why manufacturers use jigs.

The best statement I've seen of this was by David Pye. He talked in one of his books about 'workmanship of certainty' versus 'workmanship of risk'. Mass production is about certainty of dimensions, because the most expensive input is man-hours, and they can't take the time to fit stuff. The problem is that, with such variable materials the more certain you are about dimensions, the more risk you run in terms of sound. Luthiers take more risk in dimensions and get more consistent sound if they know what they're doing. The only way to have both certainty of dimensions and certainty of tone is to do material testing and sort your wood out by properties. Again, that takes time and manufacturers can't afford that. Most luthiers do some kind of sorting, even if it's just be 'feel'. Some of us do more than that.

Al, would you agree or disagree that if ( hypothetically) you where able to find identical pieces ( not necessarily flinched or consecutive cuts, but identical in material properties) that you could build identical guitars?

uvh sam asked:
"Al, would you agree or disagree that if ( hypothetically) you where able to find identical pieces ( not necessarily flinched or consecutive cuts, but identical in material properties) that you could build identical guitars?"

I would say that it ought to be possible, provided you knew what to measure and control. That's the issue.

The last time I tried making a 'matched' pair of Classicals I used flitched mahogany and redwood. Everything was controlled as closely as I could at the time. The plate weights were within 3 grams (less than 2%), the frequencies of the first ten 'free' plate modes of the top and back were within 2 Hz. Thicknesses and so on as close as I could measure The bridges were flitched, identical in mass to around .1 gram, and had the same lower mode frequencies, so I know the stiffness was the same. When I got them done they sounded almost the same, but not quite. As it turned out the 'ring+' modes on the tops were slightly different in shape, and the one with the 'better' shape sounded better. The spruce I used for the fans had a bit of 'wave' in the grain from a distant knot shadow, and one of the tops may have ended up with more fans with the wave 'up' than the other. There was no difference I could see in the assembled modes that I could look at at that time.

Since then I've paid more attention to the mode shapes than the pitches, and am getting somewhat better results. I have yet to have the time to repeat that experiment with closer attention to the mode shapes, so I can't say whether that will be the missing factor. I got together sets of wood last spring to start doing it, and then got really busy with paying work, so...

I think the best way to go about this is the slow and conservative one: start out with flitch matched sets, and match everything humanly possible. If you manage to make a pair that really end up sounding the same, then do it again a couple more times to make sure it was not a fluke. If that works you have a set of conditions that are 'sufficient'. Then you can relax them one at a time to see which ones are 'necessary'. For example, if you have two sets of top wood from different trees that test out 'identical' in properties, you can make a pair from those woods using everything else 'flitched'. If they sound the same, then you can say with more confidence that knowing the properties may be sufficient. It's possible, for example, that you could measure the same overall Young's modulus along the grain in two tops, but one would have alternating soft and hard lines where the other was more uniform, and this could introduce variance in the higher order vibration modes that would be audible.

I'd love to get on with this series of experiments. I've been saving all sorts of stuff to try out. I've got WRC and Red spruce that have 'identical' properties except for the damping factor, for example. That's an experiment waiting to be done if ever there was one, but I need to show I can make 'identical' guitars on demand before I can do it with any confidence. Once we can do that the door is open to actually getting data on things that are now more matters of opinion or theory.