Yow-yow-yowing bass strings

[Nathan Bower]

But how can we test this?

Simple. PLuck the string at a non vertical angle. If the reason for the
yow-ing is a horizontal (or indeed just non-vertical) force applied by the
hammer then plucking at a none vertical angle should also induce the same
phenomenon, and IMO exagerate it.

If not then the sypathetic "chiming in" of local strings seems more likely.

Sound valid ?

Nathan



----- Original Message -----
From: Sarah Fox
To: Pianotech
Sent: Thursday, January 23, 2003 9:34 PM
Subject: Re: Yow-yow-yowing bass strings


Hi Alan et al.,

>> Ah, you were so close to naming it. It's called longitudinal
inharmonicity, When strings vibrate, they don't just go up and down, as
sketches of string motion are drawn. They move in all directions, very
complex. Simply put, the strings in question are some combination of
damaged, poorly made, dirty, corroded, stretched out, or just old. The
motion in one or more directions is hampered in some way so the string
harmonics are "fighting" each other, i.e., not matching up, going out of
phase.

Very cool.  Now I know the name. <smile>  Just to expand on this concept, if
the impulse (i.e. hammer blow) delivered to the string has both vertical and
horizontal components, and if the vertical and horizontal components are not
simple scalar translations of each other (i.e. that the horizontal force is
a fixed multiple of the vertical force, such that they could be resolved as
a simple, unidirectional impulse at an angular direction -- highly
doubtful), then the initial horizontal and vertical spectra would have
different relative representations in the different harmonics (partials).
As a result, the resultant angle of vibration would differ between
harmonics.  (Think about it.)  Now, considering the inharmonicity of the
string, the phasing of the different harmonics would drift.  As they drift,
angle of vibration at any given position of the string would also drift,
i.e. being the sum of the vibrational components from each harmonic, which
arguably are set at different angles in an imperfect system.  Add to the
cocktail that nonlinearities in string behavior would result in the gradual
transfer of energy from lower frequencies to their harmonics in the *same*
vibrational direction as the lower frequencies, with those frequencies
summating with the (slightly different frequency) harmonics at different
vibrational angles, thus causing a shift in the angle of the resultant
vibrational component.  YOW!!  WOW!!  This could make a person's brain
bleed!

ANYWAY....  I think the answer with regard to the non-yowing Bosendorfer vs.
the other yowing pianos is probably the absence of horizontal components in
the initial impulse to the string.  That is, (1) the hammer is better
balanced on the shank, such that the shank doesn't twist when set into
motion; (2) the hammer's center of mass moves perfectly in-line towards the
strike point (not with respect to the arc of it's swing); (3) the centers
are tighter, resulting in less play; (4) the hammers are more uniform and/or
less grooved, such that the string is not "tapped" slightly to one side; (5)
other factors that you piano techs would know better than I would.
Basically, it's a more precise motion that delivers, say, a 99.5% vertical
and 0.5% horizontal blow, even after all the twisting and flailing that the
hammer undergoes en route to the string.  Perhaps the extra care in
manufacture?  Perhaps luck of the run?  Perhaps it's also partially related
to the use of hornbeam, which I recall flexes less???

I remember taking lessons as a teen on my teacher's concert Bosendorfer.
Cool piano!  I think she loved that piano like a child.  Still, I confess I
didn't enjoy it as much as a beat-up Steinway B in one of the practice rooms
at my alma mater.  The piano didn't look like much, but it sang
beautifully -- even if it might have yow-yow'ed a bit!

Peace,
Sarah