Neck profiles

Passacaglia

This is a great discussion guys, thanks.

Bones

No not at all Michael, I just wanted to make sure that I was clear that I'm just voicing my own personal, unscientific opinion and also to point out that I was mostly remarking relative to stiffness and not so much mass since I'm not really sure how mass of the neck affects tone.

Good point about neck stability and staying in tune also. That is consistent with my experience also. It does seem logical that a relatively compliant neck would be more prone to going out of tune.

Interesting topic for sure and hopefully some other builders will chime in....

dennis

i m usually not so interested in gear talk but my friend JP wrote some interesting stuff on his site:

http://gypsyguitarfans.com/technical-primer.html

i'd be curious to see what others think of what he wrote.

Jazzaferri

Michael

He wrote that in his book making an archtop guitar which I have and he said that in the DVD on the same topic that I have.

Having said that, by far and away the majority of his hand built Benedettos had Maple necks. Not exactly the lightest. :shock:

He did make an archtop gut string (with trad violin style tuners too) which he kept.

Michael Dunn agrees with him as does Jake DeVilliers. Both of whom learned to build in the classical tradition.

Me I am just reporting what a few builders who I have great respect for say.

Bob also stated that the back (presumably of an archtop) was more important to the sound than the top. There must be some magic in his guitars though as he was getting 40K for them at the end before he went commercial

Bob Holo

Dennis - I think he might be better served to reference existing books and papers on guitar acoustics. His exuberance for the topic is engaging, but if his goal is to educate people on guitar acoustics, there are many good references that can help him do that. Half an hour on google will help him find them, and by referencing vetted research papers, he can be sure that the material will give his readers the solid technical foundation he wants to provide.

On guitar necks, generally rigidity is good. What you want is a guitar neck that does not vibrate unduly with the guitar because the nut or zero fret is the terminus for one end of the string. I think Michael Bauer mentioned this. If it vibrates, it has the potential to steal energy, often in unpredictable ways that can lead to loss of power, hot or dead spots, or other anomalies. In terms of neck design, you can view your neck as a dampened member and focus on making it dampened enough to not vibrate, or you can view it as a tuned member and focus on changing its modulus to discourage it from vibrating in the instrument's frequency range. Realistically, necks are a bit of both, because having conjoined materials of different densities introduces damping, and as necks are made of a few ounces of wood and not a few pounds of stone, they do in practice vibrate a bit, so the challenge is making that vibration harmless or even beneficial to the extent that it can be. Every good builder has his preferred spot along this spectrum. The great old GJ guitars tended to be of the "too massive to vibrate much" variety, but I suspect it was more due to a lack of modern stiffeners forcing big necks than actual design intent. Modern makers have the luxury of a greater variety of performance materials which allow them to alter damping and modulus without changing the size of the neck. I've liked the necks on acoustic Benedettos I've tried. They seemed well designed to match the guitar.

noodlenot

Bob Holo wrote:

they do in practice vibrate a bit, so the challenge is making that vibration harmless or even beneficial to the extent that it can be.

Pardon the arrogance of asking you a technical question here, but the neck always vibrates, even if just a tiny bit, no? i don´t know about carbon stiffened necks, (or truss-rods), but on classical guitars the first neck mode is normally too low to interfere with the lower box-modes, but german luthier Dennis Tolz told once that if you make a pretty stiff neck that the resonance could be shifted up (maybe up to 75 Hz, IIRC - on classical guitars) to the point that it might then couple with the lower box/air resonances, extending their range (at the expense of peak amplitude) and so providing weight and "meat" to the lower end of the range. Alan Carruth seemed to agree. Is this what you mean with "making the vibrations beneficial"? just curious.
Here´s a pic from i got from Mr. Tolz, showing the first neck (or Corpus, IIRC) resonance.
Thanks,
Miguel.

Bob Holo

Yes, that's the general idea, but a person has to be careful about tuning in that way, because string tension changes the resonance frequency of the neck and so different strings and actions could change the contribution of the neck. But in general the contribution isn't disastrous because the frequency is so low that phase isn't so sharply destructive. The other thing you have to watch with all of these combined element tuning techniques is that whole "sacrifice of amplitude" part. There are many ways to increase the feel of a guitar and its general impression upon the player through hand feel, sustain, back tuning, & such. They can help give a generally "big" feel of the guitar to the player's body & ears, but they can also tend to steal from projection a little. If you're only converting 6 to 12% of the player's hand energy to sound, you want to make sure that a lot of it gets out to the audience. Also, as many of these techniques try to tune the guitar at frequencies that are right in the center of an upright bass' frequency range, you can get a guitar that interacts with the band's amplification etc. Things change depending on string type & tension, as well as the instrumentation with which the guitar will be played and the amplification techniques that will be used. At the end of the day what you really want is a guitar that a player can take on stage.

The sound and feel of a maker's guitars tends to reflect the balance they achieve, whether consciously or not, of these and other things, but I wouldn't focus on them too much particularly if you're new to building. Start with a consistent and conservatively stiff and dampened neck until you get your soundbox sorted out. Then you'll have a solid base from which to judge how it impacts your design. It's like anything else, if your basics are rock solid, then your improvisation will be that much better - but if you try to play free-jazz the day you pick up the instrument... then YMMV :-)

noodlenot

thanks for the reply, people get up early in the east coast!

yes, i´m new to building (only two under the belt, and classical guitars they are - hope one day i´ll build a Selmer, but got to take one step at a time). good call on the upright bass, that´s not much of a problem in the classical world.

cheers,
miguel.

Bones

Hmmm, very interesting.

Low E is 82.4 Hz so if the first mode of the neck is 75 Hz or there abouts it is below the lowest note on the fretboard. If the neck added a little 'boomy-ness' to the open low E that probably wouldn't be a big issue. Might be kind of a plus. Most guitars that I've played seem to have a boomy area somewhere around low A to low C or there abouts which I've been told is the 'air resonance' of the box and can be kind of obnoxious.

If the higher modes of the neck are sufficiently damped (low 'Q' in engineering terms) then it would seem that neck resonances would not really respond to higher frequency inputs but there may be some nuance there.

I have some mahogany flooring salvaged out of a remodel that is very old and dry. Full 3/4 inch thick and I've selected the flat sawn pieces to laminate together to try as necks (if I ever get back out to the shop). I think that this stuff will be pretty good since it is much stiffer than what I think of as 'standard' mahogany. It is very dark color, stiff and quite a bit 'harder' than regular mahogany (probably heavier too) but I'm not sure what variety it is.

As I recall, Bennedetto recommends rock maple in his book but qualifies that in that some people might find the weight of the neck affects the 'balance' point of the instrument especially with the massive headstocks found on a lot of archtops. Hence the massive tailpiece??? I don't know if he actually uses rock maple or just mentions it. I've used it on archtops but I've never tried it on a selmer style. Probably worth a try.

Bones

delete double post....