Re: evolutionary dead end?

Tashi wrote:
" I am beginning to respect some of what you say, however in this
shady subjective world I have a hard time sometimes, separating milk,
from butter. The subjective from science. There is also the extremely
subjective and personal interpretation and application of these
things. "

Thanks for that. you are absolutely right that the hardest jump to
make is that from the objective measurements to the subjective tone;
from what we know happens to what we like to hear. That's one reason I
try so hard to stay away from talking about 'better' results; you
might not agree with me. In the long run it ought to be possible to
find correlations between objective measurements and some subjective
judgements about instrument quality, but we're just at the beginnings
of that.

" What I meant was If the port effects the lower frequency as you
say,
reason would suggest is true as well for the higher frequencies. "

Opening a hole in the guitar body effects the different air resonances
in different ways, depending on whether the hole is in an area where
there are large pressure changes, or where the energy is represented
as flow, with little change in pressure, and hence low sound levels.
In the low 'Helmholtz' type resonance the pressure changes everywhere
inside the body at the same time in the same way, and the flow is at
the hole. Adding a hole anywhere in the surface increases the flow and
cuts down on the internal pressure change. The further away from the
main hole, and the larger the port the greater the alteration. An
intenal mode, like, say, the 'A-1', which has the air 'sloshing' the
length of the body, will be effected a lot, and in the same way, by a
hole in the side at the base of the neck, such as Ruck uses, or near
the tailblock. A hole in the side near the waist will either have
little effect on this mode, or possibly actually lower the pitch and
raise the internal air pressure, since it's on or near the pressure
node. In either case the 'normal' relationships with the top
vibrations, such as the 'long dipole' and 'cross tripole' modes will
be altered, and whether that's a good thing....... Again, in the end,
all I can talk about with any confidence is what I measured, and I'm
perfectly willling to harbor the notion that I might have messed that
up, too, if somebody can come up with better data.

" In my understanding it [altering top density, AC] would not effect
the "main air" frequency,
but this depends on your definition of the main air frequency. If you
mean the combined coupling of the air volume, and plate resonance it
would say yes. If you mean the isolated air volume frequency the
answer is no. "

Right. IMO the main variable here is the compliance of the top, which
will tend to be higher on the lower density wood, simply because the
top will tend to be lighter in weight, and possibly less stiff. It's
so easy to fall into the shorthandspeak of talking about the 'main
air' resonance as if it were a simple Helmholtz mode, when it's not.

"What I meant concerning subjective results was your experiment, and
your dismissal of any useful benefit. I don't know sometimes if
science drives us, or we drive science........ I lurk occasionally on
the Acoustic Guitar chatline. "

Actually, I don't dismiss the utility of a tournavoz outright: I think
it's likely to give the modern guitar a much more 'antique' sound, but
at the cost of a large drop in volume. Again, as I say, I'm perfectly
well aware that I need to do a better set off experiments on this, but
the physics of the thing suggest to me that the outcome is unlikely to
be much different overall, in the sense that I don't see hoow a
tournavoz could boost the trebles much. I think the outcoome has far
more to do with loss of bass.

"Agian I didn't mention anything about vibration's of the upper bout.
I simply stated an open harmonic bar lowers the plate frequincy."

It seems to me that there are two possibilities here: the pitch of the
plate drops because the stiffness of the edge is lower, or else it
drops because the vibrating area is extended more toward the upper
bout, so that the span is greater. The few holograms I've seen of tops
with open harmonic bars, iirc, suggest that the vibrating area is not
extended very much, but cutting material out of the bar would
certainly be expected to reduce the stiffness. Would you get the same
effect simply from a lower bar? Would that be structually safe?

My objective is always to futher dialog: goodness knows I can't hope
to work all of this stuff out by myself! We all have different
opinions and experiances, and sometimes it's hard not to talk across
each other. From what I know of your work I have a lot of respect for
your ability, and can't imagine that I would have nothing to learn
from your perspective.





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