[CAUT] String Coupling / SB and Bridge stiffness

[Richard Brekne]

Hi Ed, others.

I do not dispute that in a real world piano there is coupling. Obviously 
both the front and back terminations are not infinitely stiff in real 
life. I am trying to get at whether there is a connection between the 
degree of bridge stiffness and  the degree of coupling.  And whether 
this connection manifests itself in any way in the amount or degree of 
pitch drop that results from oscillating strings sharing a common support.

This has several implications actually.  One is that since coupling 
actually DOES occur in real life pianos, the bridge itself by definition 
becomes an integral part of the strings termination at the bridge and 
refutes the postulate that it is the bridge pin and the bridge pin alone 
that terminates the string at the bridge. One way or the other.... if 
there is interaction between the strings, then there must be a common 
support/termination for the interaction to take place.

Another implication is that it may be possible to diagnose stiffness 
conditions by the degree of coupling observed.  If this is true, then it 
no doubt would be a handy tool to have at hand.

Given what we already know about termination stiffness and sustain 
characteristics, I would not be surprised about the Sauter you mention.

Cheers
RicB


    If you can hear the string, it's fair to assume the soundboard is
    moving at frequencies similar to some of those in the string,
    therefore it's reasonable to assume that the bridge is also moving.
    Thus it is also likely that when frequencies are very close,
    coupling will occur. The amplitude of the wave in the string will
    play a role as well. Perhaps when it becomes too small to move the
    bridge, the strings de-couple, at least at that particular partial.

    This may not involve all the partials of the unison at all times.
    For example, in the higher octaves the first partial may become
    inaudible almost immediately. The Sauter concert grand with titanium
    armor in the top octaves is remarkable for the clarity and sustain
    of the first partials in octaves 6 and 7.

    Ed S.