Subject: acoustic coupling -- help!

Carl Lumma wrote:

>> On a loosely-related topic, sometimes a single string develops
>> what are called false beats -- a deformation in the metal
>> moves a node or some such, and the string by itself will beat.
>> Sometimes, this can be completely tuned out by changing the
>> tuning of another unison string in the group. I wouldn't have
>> believed it if I hadn't heard it several times. Any guess as
>> to how it works??

Wally adds:
>must be related to this effect. the string beating by itself is a
>very simple consequence of classical mechanics -- since the string is
>free to vibrate in two independent dimensions, any anisotropy in
>these dimensions will lead to two independent frequencies,
>corresponding to the eigenvectors of the system. so i suppose if the
>weinreich effect can pull different string's frequencies together, it
>can certainly act on both of the string's eigenvectors, assuming the
>coupling (however it works) is effective in both dimensions . . .

Gee, if it was only that complicated!
After many years of believing that false beats orginated mainly with the
wire, (which it can), I was gradually convinced it was more apt to arise
from termination inadequacies. Usually a loose pin in the bridge. Most
times, I have been able to completely remove a false beat with a light
tapping down of the string at the bridge or the bridgepin itself. On a grand
piano, this is very simple and like all instant gratifications, I try this
first.
I often must accomodate the "false beat" by detuning the other strings of
the unison so that whatever phase relationships I am fecklessly maneuvering
around will cancel, or at least, hide, the beating. This sometimes allows
me to produce a clean sounding unison where none really exists, but other
times, I simply end up with a weird note.
Oddly enough, when the false-beating unison sounds clean, it also may
refuse to sound in-tune with certain intervals. It may be a fifth that will
not allow an "in-step" progression octaves, or it may be that the double or
triple octave is whacked when the single is bearable.

--- In tuning@y..., a440a@a... wrote:
> Carl Lumma wrote:
>
> >> On a loosely-related topic, sometimes a single string develops
> >> what are called false beats -- a deformation in the metal
> >> moves a node or some such, and the string by itself will beat.
> >> Sometimes, this can be completely tuned out by changing the
> >> tuning of another unison string in the group. I wouldn't have
> >> believed it if I hadn't heard it several times. Any guess as
> >> to how it works??
>
> Wally adds:
> >must be related to this effect. the string beating by itself is a
> >very simple consequence of classical mechanics -- since the string
is
> >free to vibrate in two independent dimensions, any anisotropy in
> >these dimensions will lead to two independent frequencies,
> >corresponding to the eigenvectors of the system. so i suppose if
the
> >weinreich effect can pull different string's frequencies together,
it
> >can certainly act on both of the string's eigenvectors, assuming
the
> >coupling (however it works) is effective in both dimensions . . .
>
> Gee, if it was only that complicated!
> After many years of believing that false beats orginated mainly
with the
> wire, (which it can), I was gradually convinced it was more apt to
arise
> from termination inadequacies.

yes, exactly! that's where the anisotropy in the two dimensions can
come in with most severity. if the bridge is effectively in a
different position for one dimension of vibration than for another,
you get false beats.