Duplex

[John Delacour]

At 7:43 PM +1100 11/5/01, Overs Pianos wrote:

>... during the process I discovered that a small change in duplex 
>tension occurs when the speaking length tension is raised or 
>lowered. Now before you both reply, 'of course but the bridge is 
>rocking over with the tension change', yes it is. But something 
>extra is happening, the bridge pins are also yielding a little in 
>response to the tension changes, and this will allow just a small 
>amount of longitudinal energy from the speaking length to leak over 
>onto the reap duplex segment.
>
>Phew! I hope that made sense.


Without realizing your hope, Ron, I'd like to consider a case that 
allows less rein to the imagination.

Suppose we have a 3" speaking length terminated at the front by a 
perfectly massive over-bar under which the string passes at an angle 
of about 15° to continue for 1" up to a duplex bridge and then 
onwards over the bearing felt to the wrestpin.

I pluck the 1" front length (which itself has no musical qualities) 
and the 3" speaking length responds with a faint note at its own 
frequency.

Now I say it is inconceivable that any transverse vibration should 
continue past the bar and that the excitation of the speaking length 
must be caused by compression waves passing _along_ the wire at an 
indeterminate frequency.  At the point on the surface of the wire 
where the wire is forced up round the bar there will be impedance to 
these waves, but all the other molecules are as free as ever to pass 
on the wave under the top bridge.

I'd like to know if you, and others, think this is logical.

If piano string tone were produced only by transverse movements 
transmitted to the harmonic structure, then it would make little 
difference what wire was used.  We all know that the internal 
structure not only of steel wire but also of bass string covering 
wire has a great effect on tone and it could probably be demonstrated 
that two strings of different composition, carrying out precisely the 
same transverse excursions would sound quite different owing to the 
internal behaviour of the wire and the response of the molecules to 
the lengthwise shock.

Duplex Dan keeps talking about this Steinway patent in German.  Let's 
be having it, even in German, so we can see what Theodore says.

JD