Question:
I'm new to guitar construction and as you will see by the following a
real novice both mentally and physically in the art. I am however
committed to improve both deficiencies so here goes with my question
of the day.
I've been wondering recently what effect the stresses in an arched top
or back may have on the vibration of the wood and the final tone of
the guitar. Internal stress seems likely to affect the vibration
characteristics somewhat just as a highly stressed string changes
pitch with change in tension . I'm unaware if there has been study
on this issue and I'm curious if there is information out there that
I'm missing.
A new guitar almost always changes during the "playing in" time and
since the creep strength of wood is relatively poor I'm curious if the
stress relief which occurs after construction during this period is
responsible (largely or in part) for the "playing in effect.
Answer:
Roughly and from memory, the strings passed over the bridge at a zero degree
angle from a tailpiece. There was a clamping mechanism of some kind on
the bridge that made the string contact with the bridge solid. This
produced no downward or upward tension on the top. Obviously someone
else felt that tension has a significant effect in the tone/volume
realm.
I have had some experience with a free standing bridge/tailpiece type
model..but on flat top. There is definately a relationship to
downward tension and tone/volume. Like many things I'm sure a little
goes a long way, but "some" is necessary. I do know one experiment of
mine sucked due to too much downward tension. BTW..you header is a
bit confusing. What do you mean by wood "bending" stress ? I have
always assumed archtops where carved. I have seen some old plywood
top archtop hollowbody electrics(Harmony Hollywood) that seemed to be
steam formed/bent however.
I realize that a downward stress from the bridge is necessary and
desireable. I was referring mostly to the stress in the top which
comes about by bending the top into a slight arch. I realize that one
could steam bend the top to relieve the stresses of the bending
operation and give it a permanent "set". But I was curious if the top
without these stresses from building would sound different than one
with normal stresses. My guess after thinking more about it is that
it wouldn't make much difference since the top is being slowly
distroted by the stresses that come from stringing anyway and those
stresses are always there as long as the strings are under tension.
A well made guitar has (ideally) only the stresses associated with the
string tension. Stresses (two pieces of wood fighting each other) are
generally thought to reduce the quality of the sound. The forming of the
various pieces in the guitar is done with an intention of reducing the
stresses as much as possible. An archtop is either carved or steam bent.
This minimizes the stresses. The best makers build very little stress into
their guitars. Exactly why stress affects sound is not well understood.
The wood will also self relieve stress over time (part of "breaking in").
The wood also becomes less lossy with time (resins harden?) and the guitar
seems to "remember" the sound.
