[CAUT] String Coupling / SB and Bridge stiffness.

[Richard Brekne]

Hi Ed

Thanks for your post. Much to think about. Your raise some points about 
sounding and non sounding strings and their relationship to any given 
note that are very important and real interesting to ponder.  Some of 
this can easily get into the basic idea behind the duplex if you stop 
and think about it.  A string that is allowed to couple anywhere along 
the bridge with another string has the opportunity to either lessen 
impedance (by vibrating sympathetically) or increase it (by not having 
any partials frequencies that coincide).  This can easily get into the 
effect of a P-12ths priority tuning for similar reasons I would think, 
tho not directly related to the impedance issue. Indeed, some of my 
first posts around 2001 on the subject matter mentioned a strengthening 
and increase in clarity and sustain, especially noticable in the higher 
diskant when 12ths are used to allign octaves.  I would not be at all 
surprised to hear that Virgils musings about how tuning can effect the 
general sound of the instrument gets into this kind of thing. Thanks 
again for the posts.

Cheers
RicB

    Ric-

    Unfortunately I had to glue in some key bushings, and my mind took
    over...


Grin... Have I been there ... or someplace very similar many times ?? :):)


    In thinking about strings and soundboards, etc., we proceed by
    conceptually isolating the various components, when in reality they
    are always interconnected. Consider the role of the non-playing
    strings when you try to measure the pitch of one string in a
    tri-chord unison. They do not magically evaporate, changing nothing.
    Played or not, they effect the system.

     From the viewpoint of the sounding string, the non-sounding strings
    are increasing the impedance of the bridge/soundboard/string system
    that the single sounding string is trying to move.

    A. If the two non-sounding strings are muted, they are in effect
    coupled with their half-step neighbors, and presumably their
    impedance does not change over time.

    B. If they are not muted, but are left open when one of the
    tri-chords is plucked, they would first add to the impedance, then
    perhaps, as they began to move in response to the bridge motion,
    they might work either with or against the original string,
    depending on the phase shift.

    C. If all three strings are struck, is there an amplitude threshold
    for coupling to take place via the bridge? Is it the same as the
    amplitude threshold for the system to produce audible sound? If not,
    what will we hear when two or three coupled strings de-couple? Can
    we hear them de-couple at one partial, but stay coupled at other
    partials?  If this can be heard, it might be your diagnostic for
    system impedance. Perhaps this is the hissing sound of a killer
    octave with poor sustain.


    Meanwhile, I had an interesting talk with Virgil Smith this evening.
    He is doing well and has been writing some new material about how
    tuning can
    change the sound of a piano.
    Ed S.