Acoustic Memory

[Robert Goodale]

Hello all,

I was recently having a personal conversation with Eric
Frankson from this list, (hello Erick), regarding the
current thread on sound boards, new vs old and improvement
with age.  During this chat something kind of odd occurred
to me.  Perhaps this is a pretty big stretch but I suppose
there could be some merit that warrants discussion.  The
concept is what might be appropriately called "Acoustic
Memory".

Wood has some known properties regarding the natural places
it wants to be.  For example a piece of low-grade and poorly
cured lumber will warp and curl with the grain from it's
present position to a more relaxed position in favor of it's
new environment.  In a somewhat similar approach, a quarter
sawn and properly cured piece of wood wants to remain
perfectly straight.  If it is forced into a bend under
pressure it will return to it's previous position once the
pressure is removed.  However, if such a piece of wood is
forced into a curve and then made to stay there for an
extended period of time, (perhaps a few months or even
years), when the tension is released the wood will retain
it's unnatural curve because it has been trained to be in
that position over time.  It has "memorized" that position
and it wants to stay there.

What if we could apply this principal to the acoustic
properties of a sound board?  I'm not referring to board
crown here, rather I'm thinking of the "memorization" of
vibrative distribution within the board.  Let's look at it
this way.  Any particular note, (say A-440 for example), is
generated from a specific set of three strings, travels to a
specific set of six bridge pins, and the vibrative energy is
transferred into the board via specific conduits, (i.e.
physical corresponding wood fibers).  Once in the board the
vibrative energy originating from that particular spot is
distributed in specific calculated directions.  No other
note in the scale follows the same path, only these
particular strings produce this frequency, enter the board
at this exact spot, and travel through the board in the same
way.

what I am visualizing here is something like a vibration
table, something that you might find in a physics lab.  With
the table vibrating at a specific frequency, sand poured on
the surface of the table will dance around until it develops
a particular pattern on the surface which it then retains.
The pattern corresponds to not only the frequency that the
table is tuned to, but also by the various sizes of the
grains of sand.  If the frequency is changed the sand will
dance into a new pattern.  If the sand is replaced by
another material having a different density it too will have
it's own distinctive pattern.

So going back to the sound board, it is conceivable that a
given particular note is projected into the sound board and
then distributed into the board the exact same way each time
that note is played.  Other notes will have their own unique
patterns as well.  When different notes are played together
such as in chords the patterns blend to create a variety of
tonal colors.  The mathematics behind this must be
infinitely complex.  The concept does however help
illustrate how scale design, bridge placement, and sound
board size and shape can have such a critical and dramatic
role in a piano's tonal quality.

Where I'm going now may be a bit of a stretch but it may
have some merit.  Just like a piece of wood memorizes it's
position after being forced into a bend for an extended
period of time, could the physical properties of a sound
board at the cellular level develop "acoustical memory"?  In
other words, after A-4 has been played a few billion times
could the wood fibers responsible for distributing that
particular note begin to memorize that frequency?  It seems
possible that there may be some wood memory here just like
wood being trained to assume a bend.  If this is true then
this could help explain why some pianos seem to sound better
with age.

There are of course many other factors at play here such as
changes in crown and down bearing.  I'm not even sure if it
is possible to test this theory let alone prove it.  If this
were fact however then perhaps a technology could one day be
developed to "pre-trian" a board during manufacturing to
sweeten it's acoustical properties.  I'm not even sure how
you would go about doing this.  All of this is purely
techno-babble and may amount to absolutely nothing but it
seemed like there might be a valid concept.  Sorry if I have
tortured your brain cells.

Rob Goodale, RPT
Las Vegas, NV