Sound waves

[John Delacour]

At 8:40 AM -0800 12/7/01, Delwin D Fandrich wrote:
>----- Original Message -----
>From: "John Delacour" <JD@Pianomaker.co.uk>
>  > 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...

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.




>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

Yawn!  To quote one Del Fandrich, "We;ve read the book"

>William Braid White

Oh my giddy aunt!

>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)

discs in beech and maple?  That must be a NEW fairy story.  In my 
story book the discs live only in the abies pectinata that grow on 
the eastern slope of Monte Giavino.

>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.

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

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.

We've done "amplified".

By mystically, I presume you mean mysteriously.  So they taught you 
that the sound was mysteriously enlarged, did they?  Hmm.  It's 
unusual for teachers not to have a pat explanation for these things.

>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.

So it seems.  Do you bark when you hear engineers talking of the 
speed of sound in materials?

>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_.

>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.  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.  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.

JD