compression waves

[John Delacour]

At 6:44 PM +0000 11/23/01, Phillip L Ford wrote:

>...but could someone please explain to me the utility or application 
>of the results of this discussion.

I think it has more utility and application than many threads in this 
list, but it does require the time and willingness to experiment and 
to find and read the background literature.  A few of us seem to be 
interested enough to do that and I'd hardly expect more than a 
handful of people to take that trouble since it is a question mainly 
of piano design rather than maintenance, though I think an awareness 
of the existence of these waves can help the tuner to explain some 
otherwise mysterious nastinesses such as falseness and the 
unpleasantness of short grands.

>As I see it the items on the table are:
>
>1.  Are longitudinal modes in a real piano string determined
>by the speaking length or the total length?

Yes :-)  To what extent either is true is the only question that is 
of relevance to the pianomaker and this discussion is moving towards 
a way of answering the question.

>2.  Are the vibrations in the 'duplex' portions of the string
>caused by transverse vibration of the speaking length of the
>string and/or soundboard or by longitudinal vibration of the
>string, which seems to be caused by unknown means?

One cause of the l. waves is the sudden change in tension of the wire 
when the hammer strikes.  Only transverse waves can disturb the air 
and cause an audible sound but the two modes interact.  The 
soundboard is irrelevant since it acts simply as an amplifier (or 
absorber) of the string's vibrations and creates none of its own 
initiation.

>3.  Are the vibrations excited in the duplex portions
>transverse or longitudinal?

Both.

>4.  Do the vibrations in the 'duplex' portions of the string,
>caused by whatever means cause the speaking length to vibrate
>in its own fundamental and harmonics or in the fundamental
>and harmonics of the 'duplex'?

By design the two will coincide.


>If this summary is correct would someone please explain to me
>how answering any or all of the above questions would
>influence the scale design of a real piano.

Harold Conklin explains how he actually did this at Baldwin's.  I 
don't think anyone here is rushing to imitate his method and to me 
the interest of his method is extremely marginal.  Ellis' approach is 
interesting.  Neither would have bothered to get patents if 
longitudinal waves in piano strings did not, in some areas, cause 
problems, and the piano builder should be aware of the phenomenon and 
be prepared to meet any problems it causes.  Theodore Steinway's 
Duplex Scaling claims to improve piano tone by a certain treatment of 
longitudinal waves.  Whether the claim is valid or not, such a widely 
imitated icon of piano design, which for whatever reason has a huge 
effect on the singing and ringing properties of the grand piano, 
deserves some attention.

JD