Sound waves

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: December 05, 2001 1:13 PM
Subject: Re: Sound waves


> At 9:08 AM -0800 12/5/01, Delwin D Fandrich wrote:
>
> >If I recall, you were saying 'sound' travels through the wood. Sound is
> >waves, but it's not the same thing.
> >
> >Or, did I misunderstand what you wrote?
>
> Probably not, because rightly or wrongly I was referring to as sound
> the waves created by the string, whereas properly speaking, sound is,
> I suppose, what reaches our ears through the air as a compression
> wave produced mainly by the excursions of the soundboard.

Well, by Stephen's definition practically every moving molecule in the known
universe is part of a sound wave and since they move they all are part of a
transducer of some sort. Unfortunately, using such broad definitions of
words leaves them essentially useless for any kind of real discussion.

In light of the piano's technological history, at least in the U.S. such a
broad use of
the word is going to be very misleading. It harkens back to some very
mystical understandings of the how the soundboard works. For example:

In Piano Tone Building, The Proceedings of the Conference of Piano
Technicians (page 77), one Dr. E. W. D. Laufer, Horticulturist of the
American Steel & Wire Company, explained (referring to the figure),
"Here is a tracheid of the pine greatly enlarged. At the extreme left, a
flat view, in the center is a perspective of the little cup-shaped disc-a
minute hole cut on either side . In its center is a small membrane septum,
like to vibrator on a phonograph reproducer with a somewhat thickened disc
in its center. This is shown in plain view in the illustration on the
extreme right. It is this vibrating membrane that gives tonal value to the
woods derived from the spruce, the pine and related species. There are
billions of these membranes in every piece of pine, the view shown being
magnified 650,000 times. If a log of spruce or pine is not properly cared
for after felling, by being promptly barked, or if the lumber is subjected
to careless kiln drying instead of being air seasoned, these delicate
membranes will be ruptured, thus giving rise to inharmonics or destroying
tonal value. All the crowning or pressure put on a soundboard of this
material will not improve the tonal effect."

William Braid White, while acknowledging that soundboard do, indeed,
physically vibrate places the soundboards ability to create sound waves in
air to something
he called 'resonance.'
"The property which the soundboard possesses of reinforcing and emphasizing
the sounds generated by the strings is called 'resonance.' .Resonance may be
defined as the property which one sonorous body possesses of impressing its
vibrations upon another sonorous body. The existence of this power may be
demonstrated in a variety of ways. The most simple proofs are afforded by
the pianoforte itself."

I clearly recall attending classes many years back in which it was explained
the sound was created in the piano string, traveled through the bridges
(where it was affected by all kinds of things including the above discs) and
into the soundboard where it was somehow, mystically amplified by the above
mentioned resonant discs
and spewed back out into the atmosphere so that we could hear it.

So, like Pavlov's dogs, I bark when I hear about 'sound' traveling through
things and coming out the other end in an audible form.


> I think
> there will be no argument that the impact of the hammer against the
> string does not constitute sound, but the complex transverse, lateral
> (never mind also lengthwise) and mixed motions of the string, which
> themselves are audible to some extent, constitute the 'sound' that is
> eventually to be emitted in a more audible and somewhat modified form
> into a body of air.  I'd see it as a moot point whether you refer to
> the fully determined wave patterns produced by these motions as sound
> or not, since the complex pattern of shocks that enters the system
> contain the blueprint for the sound that emerges from it as audible
> shocks to the air that impinge on our sense.
>
> I'll leave it there for the moment so you can comment on that much
> and tell me whether I am making an error in principle here or simply
> using the word sound in a misleading way.  In other words, if I
> replaced the word 'sound' with 'shock wave pattern' or something
> unless I was talking about the shock waves that reach my sense
> organs, would I still be in error?

It makes sense to me. I would prefer to something other than 'sound,' but by
Stephen's definition, most every movement of molecules constitutes sound
energy. By that you are quite correct and my own definition and distinction
is far too narrow. I do think it is confusing--again, in the context of the
piano's technological history--to define sound in our context this broadly.
I think I will try to refine my own writing to include the phrase 'sound
energy' and work on ways to clearly differentiate between the organized
movement of molecules through steel and wood and the organized movement of
molecules through air that our ears detect as sound.


>
> >The traditional and historic model of the soundboard has sound traveling
> >through the soundboard, as you described, but this is not the way the
> >soundboard really works.
>
> Well, I'd rather get the above out of the way first, but since you're
> almost certainly going to use the word energy in your reply, I'd like
> also to have that clearly defined.  We are clearly not talking of
> electrical energy which exhibits a certain form and nor are we
> talking of nuclear energy, which is quite different; and we are not
> talking of the energy in a hydraulic turbine system.  So this energy
> is of a certain type which is seeded as x and flourishes as nx + y.
> It seems to me that "sound energy" might be a way to describe it, but
> maybe you'd question that as well.  One way or another, I think
> 'energy' is not a definite enough term to describe the phenomenon.

When the hammer(s) impact the string(s), some of the kinetic energy in the
hammer is imparted to the string(s) and is stored there as vibrational
energy. The vibrational energy in the string gradually dissipates as it is
passed into the plate and/or the bridges or it is dissipated as heat due to
the internal friction of the wire. A certain small amount is also used to
create sound directly. (Did I miss anything?)

Del