Sostenuto Puzzler

[Delwin D Fandrich]

Kent Swafford wrote:

> Hold some notes down, engage the sostenuto, play other notes and engage
> the damper pedal, release the sostenuto pedal. At this point the monkey
> does not descend, but stays up. When the damper pedal is released, the
> monkey comes down with the "crack" that the pianist complained about. (I
> noticed that when the damper pedal is keeping the sostenuto engaged, one
> can engage the una corde with no effect on the sostenuto; the monkey
> stays up.)
>
> How can this be? How can the damper pedal keep the sostenuto monkey and
> blade in the engaged position?

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Kent,

I don't know what it was that your pianist was doing, but unless I'm missing
something, using the sostenuto and damper pedals as you describe is not normal
to the mechanism.  In fact, it sounds to me as if the mechanism is working
pretty much as would be expected when used in this manner:
    1)    Play some notes and hold them down, engage the sostenuto.  Normal
operation, the sostenuto rod rotates and contacts the damper lever sostenuto
tabs and suspends the damper levers associated with the keys being held down.
    2)    Play some other notes.  The damper levers start to rise and their
sostenuto tabs contact the sostenuto rod lip and rotate, allowing the damper
lever to continue rising without binding.  The tabs do not engage the
sostenuto rod lip, but bear against it.
    3)    Engage the damper pedal.  All of the remaining damper levers rise
and all of the damper lever sostenuto tabs contact the sostenuto rod lip.  The
damper lever tabs function in the normal manner by rotating away from the
sostenuto rod lip, but they do apply an upward force against the lip.  The
sostenuto rod lip is now caught between tabs both above and below.
    4)    Release the sostenuto pedal and the pedal and trapwork assembly
returns to the normal rest position.  There is a trap spring that assures
this.  But there is only the monkey spring to return the sostenuto rod to rest
position.  It is not strong enough to overcome the friction of the brackets as
well as the spring pressure from all of the damper lever tabs holding it up.
As the damper lift pedal is released the sostenuto rod lip is released
suddenly allowing it to snap back into place and allows all of those damper
lever tabs to snap back all at once.  They make a "cracking" sound in the
process.  As would be expected under the circumstances.

Steinway did not expect that the sostenuto pedal/rod would be used in this
manner, I think.  Does it work normally when used normally and correctly?  If
so, you might consider a demonstration using a model action showing the
pianist what is happening.  I.e., teaching him/her how to use the mechanism

Regards,

Del