Impedance Matching

[Richard Brekne]

Del, Ron N. and others

Ok.. let me see if I understand this correctly so far. If we are going
to try and match strings to the soundboard impedance, we first have to
undestand a few things about soundboards. In the most general of terms
this means understanding how soundboard stiffness relates to sustain,
and how soundboard reasonant frequencies can be manipulated.

My reading so far tells me that in a stiff soundboard, the  lowest
resonate frequencies (those under 500Hz)  of the soundboard will be
higher and the peaks and valleys of those resonances will be less
defined then a less stiff soundboard. The less defined those resonances
are, the fewer problems  incured with string frequencies that coincide
with those, being sucked up by the board (ie, no sustain at board
resonances) Since there is an upper limit with regards to the stiffness
of the board (because too much sustain is also = to thin crashy sound ?)
we are left with a trade off situation.

We can effect change in these resonance frequencies by increasing or
decreasing stiffness to the board by

1: increasing / decreasing the height of the ribs, particularily in the
middel area of the board.
2: increasing / decreasing the height of the bridge.
3: increasing / decreasing the downward pressure exerted by the strings
on the bridge
4: adding / subtracting mass at various points on the board.
5: changing the tension of the strings.

(anything else ?)


The basic idea is to create a situation where the board is in general
stiff enough to radiate sound adequatly, and at the same time manipulate
the resonate frequencies so that they (as much as posible) do not
coincide with string frequencies at concert pitch ?? And at the same
time incorporate a stringing scale with decent inharmonicity
characteristics ??

I realize that this is just a begining and far from complete, but are
there any mistakes in my understanding so far ??

A couple questions here.. what is meant by the "phase angle" of the
impedance and how is this (if it is at all) manipulated. And secondly, I
am wondering if these resonant frequencies can have anything at all to
do with this buisness of para inharmonicity. Strikes me as odd that
negative inharmonicity is found primarilly in the area under 500 Hz and
only then at a few (non adjacent ??) strings,  which is the same area
where these resonanances are of most concern. I may be jumping to
conclusions there but it does strike me as a posibility.

Please inform where my understanding thusfar is lacking / directly
wrong, etc.

Richard Brekne
I.C.P.T.G.   N.P.T.F.
Bergen, Norway