S&S D Duplex

[Phillip Ford]

On Sun, 17 Nov 2002 00:56:12 -0500 Stephen Birkett
<sbirkett@real.uwaterloo.ca> wrote:

> In his patent, Theodore Steinway indicates a
> quite different function for 
> the front and rear duplexes (or should we say
> duplices)....

> As for the rear duplex he 
> notes that transverse vibrations will not pass
> the bridge termination, on 
> account of its rigidity. However, he notes that
> longitudinal vibrations 
> will pass the bridge, and designs the rear
> duplex section to provide a 
> multiple of 1/2 speaking length behind to
> bridge. To paraphrase his 
> reasoning, this will bring the longitudinal
> whistling noises into better 
> harmony with the string fundamental. [not
> passing comment on the validity 
> of his argument here - that is a different
> story - only your dog will be 
> able to tell for much of the scale].
> 
> So, to summarize CFT's reasoning ...
> ...REAR the only function
> of the rear duplex is to 
> eliminate non-harmonic whistling by tuning a
> longitudinal mode. In this 
> patent, then, both duplices were intended by
> CFT to be tuned.
> 
> Hmmm. The patent is quite specific on these
> points.
> 
> Stephen
> 

Stephen,
We've been over a lot of this in the not too distant past.  But, at the risk
of repeating what may already be in the archives, I'll make a few comments.

1.  Steinway's current building practice (and the practice for many decades)
is to define the length of the front duplex by the plate casting.  Since this
is not tunable, they are at odds with their own patent.  You might say that
they are 'pre-tuned' if you precisely controlled the plate casting and
precisely controlled the speaking lengths of the strings by plate and bridge
placement.  But neither of these things is the case, especially not at
Steinway.

2.  CFT seems pretty clear that he intends the rear duplex to deal with
longitudinal vibrations, not transverse vibrations.  If I am not mistaken, the
people who are talking about tuning the rear duplex are talking about moving
the aliquot to make the back scale length such that its TRANSVERSE vibration
is a harmonic of that of the speaking length.  Once again, this seems to be at
odds with the sacred patent.  One could make an argument that doing this type
of tuning is a good idea and will yield positive results, but it seems to me
that one would not be justified in using this patent as beatification of that
practice.

3.  If longitudinal vibrations can pass the bridge, it seems to me that they
can just as easily pass the aliquot.  So the aliquot position is irrelevant.
The plate pin becomes the relevant thing. In order to actually tune this
portion of the string for longitudinal vibrations you would need to have a
movable plate pin.  This feature has not been incorporated into any piano that
I have seen.

4.  Assuming that you could tune this portion of the string for longitudinal
vibration, how do you go about tuning something that only your dog can hear? 
And, assuming that we now have machines that could hear this for us, how did
they go about doing this back in CFT's day?

5.  If, as you say, only your dog will be able to tell over much of the scale,
why does Steinway choose to put them only in that part of the scale where your
dog would be able to tell?

Phil F


Phillip Ford
Piano Service & Restoration
1777 Yosemite Ave - 215
San Francisco, CA  94124