Recrowning/arched spruce demo

[Jim]

Hi Richard:

I stand corrected on my sloppy use of the word "amplified. "

The actual
case of the demo fork mounted on a tensioned spruce board is that the
board moves more air than the fork alone does. The fork energy is
dissipated more rapidly thru the board than thru the air around the
tines. When the board is loose, the energy is dissipated even much
more rapidly. This demo is a matter of impedance matching relationships
and has nothing to do with soundboards as found in pianos, except that
there is impedance matching in both cases, but the similarity stops
there.

Jim Coleman, Sr.

On Wed, 4 Jun 1997, Richard Moody  wrote:

> 
> 
> ----------
> > From: rhohf@idcnet.com
> > To: pianotech@ptg.org; pianotech@ptg.org
> > Subject: Re: Recrowning/arched spruce demo
> > Date: Tuesday, June 03, 1997 8:03 PM
> > 
> > 
> > First, a matter of semantics:  neither the arched spruce board nor
> a piano 
> > soundboard are amplifiers.  Amplification implies an _addition_ of
> energy to a 
> > signal.  A stereo amplifier takes a weak signal and increases it by
> 
> > electonically _adding_ energy.  Both the arched spruce and piano
> soundboard are 
> > _transducers_.  Transduction involves the passing of energy from
> one element of 
> > a system to another _without_ the addition of energy.  If a sound
> gets louder, 
> > it means that the transduction changes in some way.  I mention this
> just for 
> > clarity--it's a good idea to use the proper terms when we can. 
> 
> 	I forgot what the energy is called that is in a compressed spring or
> an arched sound board.  But as long as we are on semantics, might
> this "latent" energy some how  _add_  to the sound? Of course the
> point is  the sound gets louder whether from amplification or
> transduction.  Why this happens is what makes it interesting.  
>  
> > 
> >
> > Here is what I think is happening:  under some circumstances, a
> piece of wood 
> > can be induced to vibrate with a standing wave.  
> 
> Perhaps a clarification of the term "standing wave" could follow.  I
> might be confusing this with resonance.  If that arched demo could be
> activated such as by bowing, it should produce a note of its own.  Is
> this related to a standing wave? 
>  
> > Doing this stuff is fun and many more experiments are suggested by
> this, but 
> > someone on the list asked, "What does this mean in a real piano?" 
> The answer 
> > is, "Absolutely nothing."  
> 
> 	But then why are all sound boards crowned? 
> 
> Richard the Wonder(ing) Kind
> 
>