longitudinal mode vibrations

[Jim Coleman, Sr.]

Hi Richard:

You have jumped to the wrong conclusion about the whip ilustration. That
may have been some one else's illustration, but it is not complete. A string
with fixed points WILL have longitudinal modes as well as transverse modes.

Tie a rope to a door knob and then pluck the rope snear your tightly held
end. You will see the wave travel from one end to the other, back and forth.
This quickly sets up standing transverse waves in piano strings, but the
longitudinal mode does not go away. It is when one of the longitudinal modes
is very close to one of the transverse modes that you will hear a very
high sharp peak. Jim Hayes is working on additional patents beyond what the
Baldwin Piano Co. holds which were made by Harold Conklin when he was at
Baldwin.

Yes, plain strings also have longitudinal modes. Their problems occasionaly
show up in the Tenor section mainly, but Bass strings often show these bad
characteristics. Incidentally, there are some good characteristics also.

Jim Coleman, Sr.

On Mon, 24 May 1999, Richard Brekne wrote:

> 
> 
> > Richard Moody wrote:
> >
> > > Hi Jim,
> > >         Since no one asked, what are longitudinal mode vibrations?  How is it
> > > detected?  Can it be measured?  Is there an audible quality to it other
> > > than false beats?.  Is this a phenom. of bass strings? Is this caused by
> > > the vibrations of the sound board, so that it would appear after the first
> > > second? Maybe I have been glancing too fast over the discussions on this,
> > > but once the sound board is set into motion doesn't that affect the way
> > > the string vibrates? (which set the sb in motion to begin with?) Is this
> > > what LMV is about?
> > >
> > > Ric V's
> > > -
> >
> 
> Now I have been around the net to about 20 different universities looking at what
> their physics departments had to say about transverse and longitudinal waves as they
> relate to music instruments. What I can gather is that you can describe transverse
> waves as standing waves (Stretch a rubber band between to fingers and pluck it, the
> wave goes up and down) and longitudinal waves are traveling waves, (take a peice of
> rope and give it a whip, watch the wave move away from you)
> 
> The thing I dont quite understand is that Longitudinal waves are not really supposed
> to appear in fixed strings as there are two fixed end points which prevent the wave
> from traveling. Does this mean that piano wire is not so fixed in length after all ?
> 
> Richard Brekne
> 
>