[pianotech] Tuning the duplex sections

[John Delacour]

At 01:57 -0500 10/03/2011, George F Emerson wrote:


>...The duplex string segments, being well within 3-4 cm of the 
>vibrating soundboard, are certain to readily pick up a sympathetic 
>vibration from the soundboard if its length is consistent with a 
>frequency being produced by the soundboard, assuming the diameter 
>and tension of the duplex segment to be the same as the speaking 
>length.  For this reason, my argument would be that the vibrations 
>of the duplex string segments do not rob the speaking lengths of 
>energy required for sustain, but they recapture energy already lost 
>to the system by means of sympathetic vibrations, derived from the 
>air vibrating around them.   For this reason, I have to agree, in 
>part, with the claims of the Steinway patent that duplex scaling 
>bolsters the harmonic structure of the speaking length, and not only 
>enriches the sound, but contributes to a greater sustain, by 
>producing a more efficient system of recapturing already spent 
>energy from the soundboard.  Those who would disagree with this 
>would question if I have object measures from testing to verify 
>this.  The answer is that I do not.  All I can offer is subjective 
>observation that the tone is noticeably weakened when duplex 
>segments are muted out.

Frank, that seems to make pretty good sense generally except for the 
bit: "but they recapture energy already lost to the system by means 
of sympathetic vibrations, derived from the air vibrating around 
them", which suggests that the strings, or string sections, are 
actually excited by the air.  Without the presence of the soundboard 
and the bridge they would recapture practically nothing directly from 
the air, just as without these they are unable to produce much 
excitement in the air.  All the sharing and distribution takes place 
through the medium of the soundboard/bridge, surely.

>For the desired effect, it is, of course, critical that the duplex 
>segments match the frequencies of the harmonic partials of the 
>speaking lengths.  It is not good enough to rely on measurements of 
>lengths.  One must tune the duplex segment, moving the duplexer in 
>or out to match the musical interval defined by the mathematical 
>relationship.

That is what I have always supposed and tried to put into practice, 
but is is as obvious as all that?  We have about 60 speaking lengths 
that are always undamped.  Add to that 60 or more unlisted (not 
muted) back lengths and 60 unlisted front lengths that will be set 
vibrating in sympathy with any frequency from wherever in the scale 
that the soundboard has received.  Some of these frequencies, 
conserved and fed instantaneously back to the system are bound to add 
colour to whatever note, chord or whatever is being played.  It seems 
to me that this general effect is far more significant than the 
isolated effect of having the partial lengths of a particular string 
just right.

I had a surprise the other day which I hope to be able to understand 
in due course.  I've mentioned once or twice in the past that the 
sound of certain pianos will blossom and flourish noticeably when all 
the dampers are lifted _after_ the notes have been played and held 
down, and I see this as the sign of rather a special piano that 
allows the player to achieve effects that are impossible with most 
pianos, not possible, let's say, on a Yamaha.  Now I recently a very 
old Kirkman grand which has a very powerful and brilliant sound and 
of which I have high hopes when I get round to restoring it.  The 
piano is up to pitch but nowhere near in tune.  The sustain is 
excellent.  Now the other day in a moment of leisure I climbed over 
all the junk in its way, sat down to play it and tried the pedal 
test, holding down a chord and then lifting all the dampers.  To my 
dismay, instead of the blossoming and flourishing, there was a 
noticeable diminution in the volume of the sound.  Now I'm very 
curious to know what will happen when the piano is tuned.  What do 
you think?

JD