capo bar noises

[Dennis Johnson]

At  8:19 PM 11/14/94 -0700, Bill Spurlock, RPT wrote:

>Like Ron, I too have had the experience of eliminating string noise in the capo
>section by resorting to hammer voicing after all capo remedies failed. I felt
>like I was treating the symptoms instead of the problem by needling the
>hammers,
>since I could stop the noise by touching the front duplex section with a
>finger.
>However, some deep shoulder needling stopped it without appreciably changing
>the
>tone.

----------------------

        Absolutely!  Voicing can usually take away or minimize the noise
which remains even after shaping and cleaning the bar. But I am convinced
the real problem is that the duplex segment sympathetically resonates with
the speaking length on these problem notes.  Compare the angle of string
termination lengths by the front bridge pins with the angle of the duplex
string rest.  Ideally, the duplex should be just the correct tension and
length not to be activated audibly by the speaking length, but these duplex
lengths are approximated and cast into the plate.  That is why some notes
are problems and others aren't.  I believe that the real function of the
duplex is to enable the wire to vibrate more completely at the bar, as Ed
McMorrow described, giving more power and sustain, and less inharmonicity.
These noises are a by-product of that objective when the length and/or
tension is not ideal.  Ever wonder why we never have this problem on pianos
without the duplex?  Have you noticed that when we shape and polish the bar
perfectly, these high harmonics often get worse, or appear for the first
time?  That is because we made the string contact less under the bar and
now the duplex more easily resonates.  The real solution is what Mason &
Hamlin did years ago, individually movable duplex termination string rests.
 I can't remember if the new Masons have this feature, but they should.
The old Baldwins at least had a movable bar that we can reposition, but the
ideal place for each will not form a straight line with its neighbors.
Rather, if it was straight line it should follow more closely a mirror
image of the angle formed by the front bridge pins for each note, but that
would not fit in the space available.  Sometimes, I have taken a carefully
cut piece of felt, just the right size not to put pressure on the duplex
wire segment and place it under the duplex on the plate.  This will dampen
those high harmonics that continue to offend after mild voicing without
noticeably hindering sustain or power.  This is only a last resort however,
preferred to major needling.
        A few years ago I took the trouble on a Baldwin with the moveable
duplex termination, to calculate an ideal location for each note and it was
impossible to satisfy each note given the straight line duplex piece
(presuming a given tension).  In each duplex segment there are at least a
couple of notes that will resonate with some octave or fifth partials of
the string length.
         Also, notice how much the hall or room acoustics can effect this
problem.  Our hall has a movable stage which they change from the west to
north wall occasionally.  Against the north wall this problem is nearly
impossible- but on the west side there is no problem. Fortunately,  most
faculty prefer the west side too.   Actually, I'm not sure how this works,
because the north side is a wall of windows (if you can believe it, in a
recital hall) and somehow all high frequency noises are more audible
against that wall.  But I thought glass would absorb sound waves, not
reflect them.
        I do not know about horizontal vibrations, but it seems to me that
this would be consistent with my findings concerning the sympathic
resonance of the duplex.  Can it be that expensive to use individual,
adjustable duplex termination string rests?  Does someone not trust us with
this power?


Dennis Johnson
St. Olaf College
johnsond@stolaf.edu