Compression waves

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: November 20, 2001 7:27 AM
Subject: Compression waves


>
> I am taking as given that the compression wave is significant in the
> tone building of a piano string, though I am not at all convinced of
> this and Conklin's paper does not provide adequate data to enable me
> to verify his findings.  What the relative strength is of the sounds
> induced by the compression wave is the key point, since if they are
> so weak as to be virtually inaudible, then the whole book goes out of
> the window.

Well, sometimes they can be pretty strong. And unpredictable using normal
analysis techniques. One problem with wrapping strings according to Mr
Conklin's techniques is the precision with which everything must done. The
ratio between the core and the wrap has to be pretty exact. Even slight
variations in wrap technique could cause a problem. I did not see the
special wrap machines in operation but they were pretty elaborate.

Incidentally, I have heard a recording in which Mr Conklin set up a group of
bass strings, all of the length and and tuned to the same fundamental pitch,
in which he could play a clearly discernable tune, "Mary Had a Little Lamb,"
by his manipulation of the pitch of the longitudinal mode harmonics. I was
told his initial patent application had been denied because the patent
examiner didn't believe something or other about his application--this tape
proved the validity of his work. This demonstration may have been included
in the CD accompanying the book, "Five Lectures...."


>
> In his paper he states:
>
> >In longitudinal modes of vibration, energy propagates lengthwise
> >along the string (as periodic compressions of the string material)
> >without sidewise (transverse) motion of the string. Longitudinal and
> >transverse vibrations of a piano string can occur simultaneously.
> >However, the lowest-frequency longitudinal mode of a piano string is
> >always more than ten times the frequency of the lowest-frequency
> >transverse mode.
>
> My tests this morning suggest that this is miles from the facts and
> that it would be a meaningless comparison even if it were close.
> Bear in mind that this extract is in the context of his treatment of
> covered strings.

I was not allowed the opportunity to work with Mr Conklin. He had left the
company before I arrived and, while he was kept on retainer by the company
for several years, I was told that the company president would be most
unhappy were I to actually call on him. However, judging from his
writings--his research notes, reports, etc.--he is an exceptionally
thoughtful and careful researcher. If he writes something like the above you
can quite sure he has solid documentation somewhere to support what he
writes.


>
> The strings I used for the test all consisted of a 1.150 mm core to
> be covered with two covers in a ratio of approximately 30:70.  The
> total length between chuck and hook is about 1700 mm and the length
> of the cover round about 1300 mm.  The machine tension (which is
> irrelevant) is about 80 lbf.  The compression wave was produced by
> pulling along the bare steel a piece of doeskin covered in powdered
> resin.

The machine developed by Mr Conklin to wrap SynchroTone strings was
extensively servo-controlled and the settings were varied for each string.
Core tension was servo-controlled. The wrap wires were fed on using
servo-controlled drag devices to precisely control the tension of the copper
wire being wrapped. You don't mention the rate of rotation, but that also
was controlled and was specified for each specific string. With respect to
your string wrapping skills, I rather doubt you or anyone else could come
close to duplicating this level of precision by hand.


>
> I tested only six strings and found that the diameter of the
> undercover (owing to its mass or to the frequency of the coils ??)
> caused a change in the frequency of the wave but that the
> overspinning of the top cover caused no change.

As I recall, the wrap diameters of double-wrapped strings were also
specified for each given string. They may not--indeed, probably were
not--what you would normally expect to find. They formed a specific ratio
with the core. String tension and inharmonicity were variables, the pitch of
the longitudinal harmonic was the given.


>
> Now this raises at least a dozen interesting questions which at the
> moment I'm in no position to answer and it would probably take a
> solid week to gather the necessary data.

I don't have access to any of the research notes left by Mr Conklin. Those
are Baldwin's property and remain with the company unless someone in a
cleaning frenzy has thrown them out. (Don't laugh--that actually happened to
quite a lot of (probably) valuable research and books before my arrival at
the company. Well, it was all just a bunch of old stuff anyway. Who needs
it?) I do have a copy of his patent somewhere, however. (That's public
knowledge.) After we finish moving--once again, most everything is in
boxes--I'll try to find it and send you a copy.


>
> You say that Harold Conklin's concepts are "perfectly valid" and yet
> as a practical man and a musical man, you chose not to regard them
> and found more pleasing results in Baldwins' very factory from scales
> that did not take them into account.

That is true. For the reasons I gave before. In my experience as a piano
tuner and piano rebuilder I found that, while I might personally be bothered
by the odd and dissident longitudinal harmonic, it was quite rare for my
customer to even notice them let alone be bothered by them. They were more
bothered by note-to-note variations in power and tone color and texture.
I.e., smooth voicing.

Which brings up the issue of why I'm not particularly interested in this
whole discussion. None of it has much bearing on how I would--or
will--design a piano. I've done quite a lot of work on both front and rear
duplexes. Not enough to satisfy some, but enough to satisfy myself ... at
least for now. Enough, at least, to be willing to put many thousands of
dollars and countless hours of work into building a piano based on what I've
learned. Right now I can't see where further work along these lines is going
to give me a better piano. But I'll keep reading the stuff, just in case.

Del