Official Luthiers Forum!

Ive read a few things on the net about how old Martin guitars are often in need of a neck reset to lower the string height...often found around or above 3/16ths at the 12th fret.

Apparently this is how they were made back in the 30s-40s.

And there is usually some cautionary remarks about how the alternate method of sanding down the saddle is strictly verboten, because it would alter the breaking angle of the strings. and thus the 'drive'.

Mysterious, this word...drive.

I assume this refers to the pressure created by the string tension between the saddle and bridge/soundboard...a steeper angle means more downward force and more drive.

But does this also apply to the nut?

Is there an 'optimal' breaking angle at the nut...as well as an 'adequate' breaking angle???

I don't think it matters as long as you have an adequate break (one that allows the string to set without any buzzing). I'll stand corrected if wrong but I can't see where pushing down harder on the nut will make any difference at all. On the saddle? Yes, I agree whole-heartedly that it makes a difference.

john, the need for a neck reset is not usually due to the way the guitar was made, but rather due to the changes that take place over time. wood is not infinitely rigid, and it flexes under strain. as guitars age, the flex accumulates, leading to the need to set the neck back to the angle it originally had, more or less, in order to restore playbility, tone and intonation. most acoustic guitars will require a neck reset during their lifetime if they last for awhile.

break angle is important. too little and the guitar will lose volume and projection due to the reduction in down pressure on the saddle, and its conseqences.

there is a need for break angle at the nut as well, the slots needing to angle back toward the tuning machine posts from the front edge of the nut to provide a defined begining to the sound producing length of the string, which ends at the peak of the saddle. failure to provide the break at the nut will result in poor intonation and tone.

Ok, heres a blurb from one of my books on guitar history:

"Gibson moved from their intial 17 degree back angle to around 14 degrees in the 1970s, and many believe the tone suffered as a result. According to Gibson's Tim Shaw:

'As you increase the headstock angle you increase string tension, which gives a firmer feel and more pronounced attack.'

i really don't think he is correct. for a given string, string tension over a given scale length determines pitch. two otherwise identical guitars having the same scale length and using the same stings and tuned to the same pitch have to have the same tension, regardless of the headstock angle. and as posters above point out, headstock angle is not the same as the break angle at the nut.

there are a lot of things that affected the sound of gibsons during the period he refers to, including exceedingly poor quality control, building very heavy to avoid warranty claims, etc. any change in tone that may have occurred due to a change in headstock angle would be lost in the background.

Longer scale increases string tension. Heavier gauge strings increases string tension. Tuning to a higher pitch increases string tension. Greater headstock angle does not increase string tension.

Greater headstock angle might increase the friction of the string in the nut slot. It's not unimaginable that this could cause some very slight and subtle change in how the string responds, but you'd have to do a lot of blind comparisons to draw any valid conclusions about any truly perceptible difference this would make. People's perceptions are often determined more by what they think and expect than by what actually happens -- especially, it seems, with regard to guitars, which a lot of people think they know a lot about.

In my experience, probably 95% of what you hear or read (even from many supposedly authoritative sources) about the workings of guitars is misinformation.   

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

[QUOTE=crazymanmichael] i really don't think he is correct. for a given string, string tension over a given scale length determines pitch. two otherwise identical guitars having the same scale length and using the same stings and tuned to the same pitch have to have the same tension, regardless of the headstock angle.
[/QUOTE]Yes, I thought that was an odd use of the phrase 'string tension'. The only thing that would increase string tension for any given pitch would be a thicker guage.

But I think he must have meant downward pressure at the nut.

I can see why Gibson would move to a shallower headstock from an economic angle, as they could get away with thinner neck blanks.

I also recall reading somewhere that they switched to the heavier African mahogany at some point in the 1970s, because the lighter Honduran species was getting too expensive.

I agree with Todd Stock 100%. In the early days of modern luthiery , the builders of the day may have made good guitars but didn't truly understand the engineering behind what they were doing like they do today. This is often evident today as well.
   I look at building in 2 ways , the Art and the Science of building. The art of building is to use your ears , and gut to tell you what you have and what you want to accomplish.
   The science is applying engineering knowlege and applying the physical properties of the material to do the task you want.
As for the string tension issue , String tension is just that , any change to that will change the strings tune. The headstock angle will not change the strings physical properities to make it able to take more or less tension , that is a constant . The angle will change the stress on the headstock and the resultant force on the nut . This means the string will push down on the nut harder.
   I don't think this has much effect as the nut establishes the zero point for the scale. As long as teh string is seated there isn't that much there to add or subtract .
   Also guitars require the reset as time and stresses on the wood of the body actually pulls the back flat and rotates the neck block forward. This can be seen when you reset the neck as the fretboard extension will have to be wedged over time to accomadate this movement
   Hope this helps
john hall
blues creek guitars

Todd Rose wrote:
"In my experience, probably 95% of what you hear or read (even from many supposedly authoritative sources) about the workings of guitars is misinformation."

Amen!

One 'job' of the nut and saddle is to tell the string how long it is, by providing a firm stop. That way the string 'knows' what pitch to vibrate at. As far as I can tell, so long as the string is not hopping off the saddle top it's stopped well enough. That seems to require about a 12-15 degree break angle, which is what is usually used at the head end too. Why would you need any more break angle at the saddle than at the nut?

Well, one reaon might be because you're using a piezo pickup under the saddle. Those work best with some static load, and more break over the saddle will give you that. Even better is putting the saddle in at a back angle that bisects the break angle over the top, which gives you the maximum down force, and the minimum tipping force, for any given break angle; a win-win.

One of the problems with lowering the saddle is that the string height off the top can make a difference in the tone of the guitar. As the string vibrates the tension changes twice for every cycle of motion, and this tug on the top of the saddle increses the normal bridge torque, moving the top. This is not an efficient way for a normal guitar top to produce sound, and, in any case, the forces involved are much lower than the transverse (idealy, up-and-down) force of the string on the bridge. Still, that twice-per-cycle pull can contribute to the timbre of the instrument. The higher the strings off the top, the more of this you get.

The problem is that people raise or lower the saddle, hear the change, and attribute it to the alteration of the break angle. You can lower the saddle height and ramp the strings to keep the break angle the same, and then you'd have a better idea of which thing it is that's effecting the tone.

Players often use 'tension' to decribe the way the strings feel. Raising the action, for example, is percieved as an increase in 'tension', even with the same strings, since it's harder to push them down to the fretboard. It's no use to argue with them about this so long as they ae using one definition of tension and you're using another. First you have to specify what you're talking about. It's hard to see how a change in break angle could alter the feel of the strings, but I suppose it's possible.

finally, remember that all categorical statements are false.

Double Amen!

One of the greatest frustrations i have had as a lurker and a soon to be beginner of my first prototype of something that i hope will end up looking slightly guitar-like... is wading through all the hype and conjecture on these forums. Joe says "A" and Sam swears by "B" but Jerry says he has proof that it's "C" (but only if it's Koa) all while Guido says if you use Koa you'll be sorry!

*sigh*

My conclusions at this point are:

- that 80% of a great guitar is in the top, 15% in the rest of the instrument, and 67.2% in the mind of the guy holding the guitar. Anything left over is marketing.

- You can make a good top great but you can't make a bad top good and it's probably easy to make a great top fair.

Rob

[QUOTE=RobLak]
One of the greatest frustrations i have had as a lurker and a soon to be beginner of my first prototype of something that i hope will end up looking slightly guitar-like... is wading through all the hype and conjecture on these forums. Joe says "A" and Sam swears by "B" but Jerry says he has proof that it's "C" (but only if it's Koa) all while Guido says if you use Koa you'll be sorry!

*sigh*[/QUOTE]
Yes, but you get that in just about every field of human endeavor...except maybe mathematics???

I see all advice as a 'resource' - that I can use to experiment with and draw my own conclusions, not as divine revelations.

Thanks to all who replied!