Re: Thoughts about Cedar tops. . . .

On Aug 2, 2:10?pm, alcarruth <alcarr...@xxxxxxx> wrote:
WRC is, on average, a bit less dense than most spruces, and has lower
damping. The long-grain stiffness of all the 'usual' top woods scales
pretty much with the density, but a low density wood will generally
result in a lighter weight top when everything has been taken into
account. Cedar can have outstanding crosswise stiffness. So, as far as
I can tell, most of the acoustic benefits of using cedar come from the
fact that the top tends to be a bit lighter, which gives more power,
all else equal, and the low damping, which tends to help the high end
sound. That, at least, is the 'simple' explanation.

Cedar and redwood both share the low damping characteristic, and also
a tendancy to split. I often wonder if the two are related. Anyway, I
have always felt it to be a good idea to make the bridge footprint a
bit bigger on cedar and redwood topped guitars, to help keep 'body and
soul' together, as it were, by spreading the peeling stress out a bit.
I've seen bridges come up on cedar tops because the wood failed, when
the glue joint was fine.

The redwood I've measured has all been about as dense as most of the
spruces. Dent resistance seems to go with higher density, alas.
Englemann spruce, which is often on the 'light;' side also has more of
a tendancy to dent than, say, Red or Sitka.

Many violin makers these dys are putting a very thin patch of veneer
on the inside of the top where the soundpost sits, to help keep it
from denting. These are small, though. Considering the mass of the
glue I wonder how much benefit you'd get from putting a thin veneer of
spruce, or something harder, on a cedar top, You'd be likely to negate
the weight saving of the low density wood.

The main advantage of the 'double top' is weight saving: they can be
as much as 40% lighter than a comparable solid top for the same
stiffness. I'm told that the sound of the wood is retained, at least
to some degree; cedar sounds like cedar and so on. Those who have
mixed 'skin' types say that the outside skin seems to determine the
timbre, iirc. Why that should be...

Just to set the record straight: 'double' or 'sandwich' tops use two
layers of veneer, often no more than .5-.6mm thick (.020-.025") with
some sort of light weight core. These days the core is usually Nomex
honeycomb, with cells about 1/4" on a side, but people have used wood
(DeJonge), foam plastic, and probably other materials.

The Smallman 'lattice' uses carbon fiber and balsa to build a lattice
of I-beams in diamond-shaped units, perhaps a couple of inches apart.
thjese provide all the strength and stiffness of the top, with the
'membrane' filling in the spaces often about .5-.8mm thick. Smallman
builds the whole thing on a 'plywood' rim that acts as both top
bracing and liners. Several people, including one of my students, have
used various sorts of wood lattices without the carbon fiber. The
weight saving is less, but they are interesting and can work well. The
main drawback of the carbon-balsa lattice is that it's hard to 'tune'
for best response: it either works or it does not.

Alan Carruth / Luthier

I suppose the choice of Balsa to mate with the carbon fiber is
entirely do to the weight saving benefit? What I mean is, I know
Balsa is light, but is it also a low damping material? Maybe Basswood
would be better in that department?

Best wishes,

Dr. Jim Lowther

.

Relevant Pages

  • Re: Thoughts about Cedar tops. . . .
    ... but a low density wood will generally ... Cedar can have outstanding crosswise stiffness. ... have always felt it to be a good idea to make the bridge footprint a ...
    (rec.music.makers.guitar.acoustic)
  • Re: Thoughts about Cedar tops. . . .
    ... but a low density wood will generally ... Cedar can have outstanding crosswise stiffness. ...
    (rec.music.makers.guitar.acoustic)
  • Re: Thoughts about Cedar tops. . . .
    ... WRC is, on average, a bit less dense than most spruces, and has lower ... but a low density wood will generally ... Cedar can have outstanding crosswise stiffness. ...
    (rec.music.makers.guitar.acoustic)
  • Re: Thoughts about Cedar tops. . . .
    ... but a low density wood will generally ... Cedar can have outstanding crosswise stiffness. ...
    (rec.music.makers.guitar.acoustic)
  • Re: Narrow vs Wide grain
    ... The way to do this is to find wood that has a high ratio ... Grain counting is one such test. ... stiffness, density and damping factor, which tells you how much energy ... end we luthiers don't make guitars out of statistical abstractions, ...
    (rec.music.makers.guitar.acoustic)