Rear Duplex... very long...

[Brian Trout]

Hello Richard,

I couldn't resist giving my two cents on the subject, although I'm sure
there are others out there who are much more knowledgeable.

We see quite a variety of designs (backscale and rear duplex).

Some pianos have it set up so that the string goes directly from the rear
bridge pin to the hitch pin.

On some, the string goes from the rear bridge pin to a felted bearing
surface (part of the plate) and then on back to the hitch pin.

On some, the string goes from the rear bridge pin to an unfelted bearing
surface (part of the plate) and then back to the hitch pin.

Still others have the string coming off the rear hitch pin to an aliquot bar
of some type before going on back to the hitch pin.  The varieties of these
that come to mind are 1) a fixed single unison aliquot, 2) a movable
(tunable) single unison aliquot, and 3) an aliquot bar which would still be
movable, but only as a unit.

It appears that there has been a lot of experimenting going on over the last
century as to what is best.  Perhaps the perception of best is in the ear of
the listener.?

It would seem logical to me that the pianos with aliquots, either fixed or
movable, single or bar type, were intended to allow that back section of
string length to speak.  (Perhaps this is where the term rear duplex came
about.) Just what this adds to the overall tone production / projection
could be the topic of a very long book.  Some appear to have been designed
to speak at random, and others appear to have been designed to speak at a
particular harmonic of the speaking length.

Some examples...

On newer Baldwin pianos, the string comes off of the back bridge pin
straight back to the hitch pin.  I do not know if these lengths were
actually designed to speak or not, but they do, at least to some extent.
There is not nearly so precise a termination point at the hitch pin
(vertical) but those segments do kind of speak in a random type fashion.

On some of the old Mason & Hamlin pianos I've seen, they were using a
movable single unison type of aliquot obviously designed to divide the rear
portion of the string (behind the bridge pin) into a length that would speak
with a specific partial of the speaking length, varying from the same pitch
in the highest unisons, to a fifth above, to an octave above, to an octave
plus a fifth, to two octaves above the speaking tone as you went down the
scale.  (It's been a while, so I don't remember specifics.)

On most Steinways, there's a setup with an aliquot bar which on some you'll
find sort of 'tuned', and on some you'll find not in any particular tune at
all.

On many pianos, the lower portion of the backscale is muted, as the lower
sections tend to give off tones that people can find pretty objectionable at
times, but on most of the designs I've seen, the upper two sections are
usually the ones set up to 'sing'.

Two things come to mind as 'concerns' of backscale design, which I really
don't have specific answers to.  1) I would think that a backscale of any
kind should be of sufficient length so as not to 'clamp' the natural
movement of the soundboard oscillation.  I'm thinking that having a duplex
scale laid out that was too close to the rear bridge pins could have an
adverse affect upon the soundboard's freedom to move. (Similar thought as
having the hitch pins too close to the rear bridge pins.)  And 2), I would
suspect that there would be those who would argue that having a rear duplex
tuned either to the same frequency, or to a partial of the frequency of the
speaking length of the string, could bleed off energy from the speaking
length, and have a detrimental effect upon the tone produced.  In light of
the physics of the thing, if the energy is bled from one speaking segment to
another speaking segment, have we really lost significant sound energy?  I
don't know?  I'm asking?

I don't have clear-cut answers.

I've seen the systems that Baldwin has used with the vertical hitch pins,
and I'm impressed that it's a pretty good system.  It's very unrestrictive
of the soundboard movement, and I believe it does indeed help in good tone
production, especially in the bass.  I can't say that I've heard the kind of
clarity and purity of tone in the treble that would be pleasing to me, but
there are often other factors at work there as well.

I've also rebuilt a few pianos with tunable aliquot type duplex scales and I
have found them to have a very sweet, perhaps settled and harmonious, tone.
I've not noticed an undesirable 'bleeding' type of effect in the treble, but
I've not run any experiments.

Where does it lead?  Well, if everyone was in agreement as to which system
is best, I would suppose they would all be the same.  But for the most part
they're all a little different.  Perhaps this is one of the factors of piano
construction which, at least in part, gives a piano it's 'characteristic
tone'.

Wow did this get long!  Talk about taking up bandwidth!

It is indeed an interesting topic, and one that is probably all too often
neglected to speak of greater things such as crown and downbearing.  ;-)

On a less technical note, it's a beautiful day here in S.E. Pennsylvania.  I
hope you all are enjoying your part of the world as well.

Best to you all,

Brian Trout
Quarryville, PA
btrout@desupernet.net

----- Original Message -----
From: Richard Brekne <richardb@c2i.net>
To: PTG <pianotech@ptg.org>
Sent: Saturday, September 25, 1999 2:38 PM
Subject: Rear Duplex


> List..
>
> Been reading through several posts written earlier which touch on
> Backscale design, stringing proceedures, scale design and inharmonicity
> problems. One thing that comes up is that the length between the back
> termination point (for the non speaking length behind the bridge) and
> the back bridge pin, is often refered to as the rear duplex. At the same
> time it is stated in some of these posts something to the affect of
> "there is no defined porportional relationship between the speaking
> lenght and the length of the back scale (which seems to be the other
> term used instead of rear duplex). My question is whether or not this
> non speaking lenght should be considered as duplex at all. In most
> pianos (my experience) it seems that plucking this area results in
> almost no sustained tone, often not even a real tone but a kind of
> deadish resemblance of tone. Compared to even subdued front duplexs I
> cant see how this length of the string can contribute much (at least
> directly) to the sound production. If it doesnt serve this purpose, why
> is it called by many a "duplex" ??
>
> Richard Brekne
> I.C.P.T.G.  N.P.T.F.
> Bergen, Norway
>
>
>