Duplex

[Delwin D Fandrich]

----- Original Message -----
From: <Duplexdan@AOL.COM>
To: <pianotech@ptg.org>
Sent: November 07, 2001 8:51 PM
Subject: Re: Duplex


>
> On the other hand, you seem to be wililng to acknowledge that energy is
> transferred and the pitch of the duplex scale does have an effect on the
tone
> of the speaking length. To that point I would like to mention a slightly
> different viewpoint that may be worth your consideration. And that is the
> specific response of the duplex portion of the string to the activation of
> the speaking length.

"Transferred" is not, perhaps, the word I would use. When a hammer strikes a
string set it causes them to vibrate. This vibration is felt at the bridge
which causes it to move. The bridge motion will be mostly up and down (in a
grand) but there will also be some rotational motion. Since the bridge is
now moving the backscale must move with it. If some strings are of such a
length, tension and mass that they are sympathetic with the frequency of the
vibrations driving the bridge they will vibrate in sympathy with the
vibrating energy driving the bridge. I'm not altogether convinced this is a
good thing.

Going beyond this obviously simplistic explanation let's keep in mind that
there is more than one string segment making up the backscale of the typical
piano. When the bridge is driven into motion all of the strings making up
the backscale are forced to follow whether they are physically part of the
string making all the commotion or not. Which means that a string having the
right combination of length, tension and mass that is, say, half and octave
or two octaves away might also be vibrating in sympathy with the driving
string.


>
> ....At the moment, my best view is that the bridge pins do indeed stop a
> great deal of the energy between SL and DL but not all of it. Since the
> bridge pin is not a hitch pin, it can't  So what goes across the bridge?
And
> then , what comes back?  Isn't the string alive even though a great
portion
> of its energy is curtailed?

I don't think anything 'goes across' the bridge. Not if the bridge and
bridge pins are in reasonably good condition and there is a reasonable
amount of bridge pin offset. It doesn't really have to. The bridge itself is
moving. Anything attached to the bridge must move in sympathy with it.


>
> So my view is not that there is a resonant response of the duplex scale
> portion of the strin producing an actual tone that blends or detracts from
> the speaking length, but
> rather that the course of energy going from SL to Duplex , around the
hitch
> pin and
>  back into the speaking length directly does affect the vibrational
> consistency of the speaking length.

"Around the hitchpin and back into the speaking length...?" I sure don't see
how. Unless you're thinking of longitudinal mode harmonics which, if I
understand them correctly, are not necessarily (or even usually) harmonic to
the fundamental. In other words, they tend to be dissonant.


>
> Using a Reyburn Cybertuner, I would take a subject specimen piano with a
> perfectly tuned duplex scale and take all kinds of reading from it. Then I
> would mute the duplex scale entirely and take a second set of readings.
> Thirdly I would de-tune the duplex to "dissonant" (non low partial tones,
> such as sevenths, flat ninths,) and take another set of readings.
Fourthly, I
> would mute the dissonant duplex and take a fourth set of readings.
>
> Tis would be an interesting project, don't you think?

Interesting, perhaps, though I'm not sure what it would prove. And in the
meantime I'll concentrate on trying to figure out if there really is an
optimal backscale length.

Del