Compression waves

[John Delacour]

At 12:12 PM -0800 11/20/01, Delwin D Fandrich wrote:

>From: "John Delacour" <JD@Pianomaker.co.uk>
>  > The compression wave was produced by
>>  pulling along the bare steel a piece of doeskin covered in powdered
>>  resin.
>
>Just one more thought...piano strings are struck, not stroked.

Hey!

>Since they do respond differently when they are bowed perhaps they 
>also respond
>differently when they are stroked.

Bowing will produce a transverse wave unless you drag the bow 
lengthwise along the string, which would be a pretty uncomfortable 
way about it.  Hammering the end of the string would produce a 
compression wave so slight as to get lost a few hundred molecules 
along the wire.  The only way to produce an audible and recordable 
pressure wave along the wire is to pull the molecules at the surface 
along the wire so that they produce a domino effect as they crash 
pack against their neighbours and they all totter in turn.   This can 
be done with a grease-free finger wetted with water or spirit pulled 
along the wire but a leather covered with resin allows molecules all 
round the wire to be displaced and a regular pull will produce a good 
clear measurable note good enough to pitch by ear or register on an 
electronic sensor.

How these lengthwise waves actually come to exist to any noticeable 
extent in a string that is struck at a right angle, and how they 
affect and are affected by the transverse waves so produced is dealt 
with, as I mentioned, in Ellis' patent.  The process is roughly as I 
had pictured it in my ignorance, but he describes it in the light of 
much experimentation with proper equipment.

I find the topic very interesting and had never given it any thought 
until I read Steinway's patent, which Clark was good enough to post 
to the list.  Though I had mentioned longitudinal vibrations in the 
oil drum duplex debate, I admit I was flying a kite, as I sometimes 
do, and under torture would have confessed.

Conklin and Ellis give substance to these waves and provide very 
useful food for thought about the perfecting of the tone in the bass 
and the low tenor.  After that we get into an area where the 
frequency of the compression waves and their overtones makes them 
inaudible and then we get into Steinway duplex territory, which seems 
to me a completely different basket of prunes.  When Steinway talks 
of longitudinal waves, in strings less than a foot in total length, 
what of any significance can he be talking of?  I think there may be 
something in it, but what?  As Ron N. has said, he's unfortunately 
not around to be questioned.

JD