Official Luthiers Forum!

Thanks again to all who have replied .This has helped me a lot.
Alex I think I might give it a try with the software tone generator and loud speaker . Where and how do you put the speaker on the guitar? By the way I think your second guitar sounds very impressive. I never thought that nylon strings could sound so good What are the specs for it? How did you record it?

Craig.

Craig,

Thanks! (hoping you are not making fun of my poor playing ) The mic is a Samson C-01U. It's an affordable but decent condenser that uses USB and needs no preamp. By far best bang for the buck.

I have used this one:
http://www.nch.com.au/tonegen/index.html

When the demo expired i switched to one made by a russian team. It does not have an expiry, but the sound cuts every 15 seconds of use so i need to restart it, pretty annoying so i might buy the nch one soon.

I am not using a single speaker, but my stereo's loudspeakers. My workshop is actually a small table, a case of handtools and a vacuum cleaner in my office
You just need to get close enough to activate the guitar and feel smth happening on its surface. You can even stay 10 feet away of it but then you'll need a lot of noise for that. You just need to find what works best in your shop. You need to be able to access the mouse/kb as well to sweep the tones.

The guitar is Italian spruce, spanish cedar neck, indian rw back sides and bridge. Body size medium. Usual fan bracing. The top main mode is somewhere between F and F# (app. 180 Hz) and the lower bout of the back 220 Hz.
When i first strung up the guitar it was at G 196 Hz, which is probably the ideal mode. But the guitar felt too closed in so i shaved both braces and top a little until i felt it opened/warmed up. I think that forcing the opening like this takes away some of the overtones and overall sound complexity. I left my third (latest) a bit stiffer (G# 207 Hz) and I'll wait and see what a few months of play in do.

In the end I need to add that the difference in thicknesses between say G# and F#, the range where most good guitars fell in, is quite big. Maybe spruce of 2.4mm vs 2.0 with same bracing? Both can work well if all ingredients are right, (say balanced). Arriving at a certain note will definitely not make a good guitar on its own.

_________________
Build log

Please forgive me for taking this back to the neck mode,

I said,

I have always thought that 12 fret slot-head instruments had the fullest sound(subjective). For some reason It clicked this time when reading your explanation of the neck mode.

Is it possible there is a two fold reason for this both having to do with the neck mode?

#1 The obvious is the shorter lighter neck is more likely to couple with the top mode as stated.

#2 On the 12 fret neck the neck block is closer to the nodal point thereby reducing the damping effect upon the neck mode ?

Dang, concentration probs, some times in an effort to boil down what I mean to say to a simple statement it changes into something totally different.

Please bear'e with me.

Al Carruth said,

In a way you can think of the whole guitar as a sort of funny shaped wood bar. The whole thing can vibrate in different ways, just the way a wooden ruler does. If you support a 12" ruler at two points, about 2-1/2" in from the ends, and tap it in the middle, it will vibrate freely, with the middle going 'down' as the ends go 'up'. On the guitar, the stationary points (nodes) are somewhere around the nut or first fret, and a line roughly across the wide part of he lower bout. The upper block area is an 'antinode': it moves a lot. If I'm thinking in 'technoid' terms, I call this the 'first corpus', or C1 mode, and that's how I lable it on my data sheets.

OK so I took this and ran with it and maybe incorrectly,

So I should have said,


#2 On the 12 fret neck the neck block is closer to the point of most excursion thereby reducing the damping effect upon the neck mode ?

Because the guitar is under tension I feel the nodal points are effectively moved to the nut and saddle, they are also the points that supply the energy that drives this all.
The twelfth fret is the center point of all this and wants to be the point of most excursion. The headstock and area behind the bridge are just taken for a ride. Their balance or imbalance may move the point of most excursion a bit.
On a fourteen fret guitar the weight of the heel and neck block is not centered at the point of most excursion and has a dampening (break up) effect.

also

Because of the way a guitar is constructed it seems possible that a point very close to the end of the heel block acts more like a hinge point.
So on a fourteen fret neck this hinge point is further away from the place that wants to be the point of most excursion. This would also unbalance things and have a break up effect.

??????????????????

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

K.O. wrote:
"Because the guitar is under tension I feel the nodal points are effectively moved to the nut and saddle, they are also the points that supply the energy that drives this all."

I haven't checked that out specifically, but I can't think of any reason why tension on the string would alter the nodal points. The frequency, maybe, a little, but not the locations of the nodes.

Anyway, rather than go on what you believe to be true, why not get some data? Support the guitar up off the bench with soft pads at the nut and saddle line, and drive it with a speaker. You can often feel it move well enough to get a pretty good idea of where the node lines are; you usually can't get enough amplitude to actually move glitter. Check it out with and without string tension, and see if the nodes move.

Be careful! It's really easy to see what you want to see. Unless there is a pretty big change, I'd be skeptical. This is a fairly extraordinary claim, and will require extraordinary proof. For one thing, if you're right, we have to figure out how to explain why it happens, and that might be tough.

Of course, it's possible that the node lines _do_ fall at, or near, the nut and saddle. This would tend to work well, since it would be hard for the strings to drive that vibration directly, and you'd end up with better sustain. I've noticed that this seems to hold true for the successful solid body guitar designs, and I think it's one of the problems with solid body basses. They have the bridge 'way out at the end, where the thing _has_ to be moving a lot, and then wonder why they get 'dead' notes.

These sorts of things are perfect examples of the efficacy of cultural evolution. Lots of folks try lots of things, and some of them work better than others. The next generation of things are all variations on the most successful designs, and some of them work better still. Nobody has to know _why_ something works, they just have to mess around a little with the more successful designs, and things will rapidly approach a very high funtional level. This is why it's so hard to improve on the good designs, and why most of the 'radical' new stuff doesn't work as well as you'd hope, no matter how much 'science' went into it.

To my mind, the best use of science in lutherie is to figure out how the good designs we have work, and why they sometimes don't. We can also use it to figure out stuff like good wood substitutions, for when we run out of all the traditional stuff. Once you understand how these things work you're in a better position to make real improvements.

Craig this might help you visualize things.

http://www.kettering.edu/~drussell/guitars/hummingbird.html

at the bottom of the page you can click to see other experiments

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Thanks Alex for the links and info and no I wasn't making fun of your playing. I have always been a steel string fan but I think I might be mellowing as I actually really liked the sound of your guitar. I have downloaded the software and will try it out in the next day or so and will report back what i find.
Thanks again
Craig.