Sound waves

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: December 07, 2001 12:59 PM
Subject: Re: Sound waves


>
> Maybe, but I'm not Stephen.  I said that sound is always a
> compression wave moving through a medium, that the sound is fully
> defined by the oscillations of the string initiated by the blow of
> the hammer and that it reaches our ears as a compression wave emitted
> mainly from the soundboard.

That's good, except for the 'fully defined by the oscillations of the
string' part. The soundboard assembly also acts somewhat like a filter in
that it doesn't respond to all of the vibrations/oscillations in the string
nor does it doesn't respond uniformly to them.



> Forgetting the smokescreen of the discs, how do you presume the sound
> gets there?  By cosmic transmigration?!

I don't know. It's not my theory.


>
> The sound is clearly not created in the hammer.  The sound is formed,
> defined, given its blueprint or what you will, by the string as a
> result of the blow from the hammer.
>
> "Spewed into the atmosphere" is your expression, used for your
> purposes apparently to express disbelief either in our hearing or in
> the compressibility of air.

It expressed, or attempted to, my disbelief in the theory I was
describing/quoting. It was not my theory.


> >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.
>
> But the organization, the pattern, the 'shape' is the _same_.

The movement of the soundboard that creates the compresson and refraction of
air molecules is not an internal compression wave. It is the physical
up-and-down movement of the soundboard panel in response to the vibrating
string that does that.


>
> >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?)
>
> Well I've never heard of "vibrational energy" and though I know what
> you mean and it is an acceptable description of the phenomenon, I
> don't see the need for a new term.

It's not a new term. It's been used for many years to describe this
phenomena.


>
> Sound is energy -- a particular
> form of energy, which propagates by causing oscillations of the
> molecules in the conductive media, namely a compression wave.
> "Vibrational energy" adds nothing at all to what we have already in
> the way of terminology.  I also think it would be pointless to take
> the discussion of "sound" into the realm of philosophy, or we might
> be able to argue in the end that matter itself does not exist, as my
> dear Berkeley does.
>
> It seems to me, too, that Stephen's identification of sound with all
> sorts of waves is rather hard to swallow.  My conception so far is
> far more closely bounded, but I remain to be enlightened.  I'm trying
> to get a clear understanding, and that's why I'm engaged in this
> discussion, and not to pit my wits against anyone else's.  From what
> you or Ron or Stephen say I am getting a clearer picture of your
> various views on the matter and actually gaining some knowledge as
> well, but I'm only at the beginning.  You seem to believe your
> understanding is complete but seem unwilling or unable to demonstrate
> that.

I'm not sure what you mean by this. No, I don't think my understanding is
complete and I have been attempting for years to explain and demonstrate
what knowledge I do have.


>
> What I'd like to do is discover as fully as possible
> everything that happens between hammer and heard sound, and that's
> quite a lot.  Ron has offered to draw me into the impedance question
> again, and I'm looking forward to that, but there are more basic
> things to clear up first and impedance will arise as a clarification
> of later questions.  I have enough empirical understanding of
> impedance to get by with for the moment -- the calculation of it and
> its use as a scientific design factor can wait a little.

I'm not sure anyone has the mathematical tools to calculate the impedances
of a working soundboard. It's relatively easy--given the right equipment and
some time--to measure it after the fact and it can be broadly predicted
based on a general understanding of the basic principles, but I doubt we'll
see the day anytime soon that it will be calculated with any precision.

Del