Backscale design... Del, anyone?

[Delwin D Fandrich]

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Brian Trout wrote:

> I've been wondering if anyone, Del, Ron, or anyone who has a knowledge of
> scale design would like to pick up on this.   Is this referring to the
> length of string between the rear bridge pin and the hitch pin that often
> speaks in the treble end of the piano?  I've rebuild an old Mason & Hamlin
> with the 'half round' aliquots in the rear duplex scale, and tuned each one
> to perfection... very sweet sound.  Is that what you were referring to,
> Del? Is it also important to have the sections of strings that we often mute
> (the part of the string between the rear bridge pin and the hitch pin of the
> wound bass strings for example) in some type of proportional relationship to
> the length of the speaking length of the string?  (I sure hope that came out
> right.  I've never asked this question before!)  Would that be a possible
> reason to actually shorten the speaking length of an already short bass
> string?

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Brian,

I think that Ron covered most of it.  But, just a few thoughts in passing --

1)    Yes, what I call the back scale is the portion of the string(s) between
the back bridge pin and the back string termination point.  This could be the
brass counterbearing bearing bars you mentioned, the cast aliquot bars that
Steinway uses or the vertical hitches that Baldwin uses.  Whatever the
manufacturer chooses to terminate the back section of that string portion
with.  By the way, this is my terminology.  I couldn't think of any other name
for it and I couldn't find one in "the literature."  If any one else knows of
a formal name for this part of the stringing scale, I be delighted to learn of
it.

2)    I am not yet aware of any particular proportional relationship between
the length of the speaking portion of the string and the length of the back
scale.  This is not an "all or nothing" situation.  The closer the back
termination point is to the back row of bridge pins, the more restricted will
be the motion of the soundboard so there are some definite minimums that
should be observed.  For example, in the high treble section some pianos use
aliquot tuning that makes the back scale length 1/2 of the speaking length of
the string.  This is too short.  It binds the soundboard and severely
restricts its motion.  Especially if the string downbearing (i.e., downforce)
ends up being a bit excessive.  And, yes, to some extent back scale length and
string bearing are inversely related.

For a variety of reasons, most small pianos use back scale lengths that are
excessively short.  Especially in the mono-chords.  An effective back scale
length of 45 mm is simply too short to allow the bridge and soundboard any
freedom of motion.  Coupled with the excessively large core wires used in some
of these piano it becomes impossible to achieve any kind of fundamental bass
response.  Even in very small scales I would like to see a back scale length
of at least 75 mm or so.  (I also went into this some in the articles on small
piano scales a couple of years back.)

3)    Most small pianos have mono-chord bass strings that are too long for the
size of the piano they reside in.  There is good reason for this -- well, at
least there is a historical reason even if it's not a very good one.  Most
piano designers of the late 1800's and early 1900's believed this was
essential.  For example, Samuel Wolfenden, in "A Treatise on the Art of
Pianoforte Construction" wrote, "It is vital to make bass strings as long as
they can be consistently with placing the bridge upon a part of the belly
which can respond to the action of the strings; and so the expedient of a
suspended bass bridge has come into fairly general use.  Its value is far in
excess of its small extra cost."  William Braid White was also an advocate of
the longest possible speaking length in small pianos.  Any problems this might
introduce could be solved by using the bass bridge suspense: "for it is
possible by means of the suspension belly bridges, to increase the actual
speaking lengths several inches."

This principal seems to have been accepted at face value for decades.  My
research, however, has shown that it simply is not true.  A more acceptable
balance between the speaking length and the back scale length must be
maintained if the piano is to produce a pleasing bass tone.  If a longer
speaking length is desired, the piano should be made longer.

We regularly shorten the speaking length of the low bass, especially in
smaller pianos.  That is, most anything below about 200 cm.  At the same time
we remove most of the bass bridge cantilevers that we encounter.  Only when
the customer insists on maintaining visual authenticity do we retain it.
Removing the cantilever and shortening the bass scale does involve laying out
a new bass bridge scale and making a new bass bridge body -- neither of which
are exactly rocket science.  As we are usually laying out a new rib scale as
well it is a fairly easy matter to position the ribs under the new bridge body
to provide adequate support for the new bridge.

As Ron mentioned is a second post, if there is still a need to provide for
additional flexibility in the lower (i.e., the bass) portion of the
soundboard/bridge assembly, it can be done most simply by undercutting the
bass bridge as required.  I first used this type of bridge in a piano I
designed for Baldwin and later in the Walter grand.  It accomplished the same
acoustical purpose of the cantilever without the additional mass and torsional
stresses introduced by the cantilever.  We now use this design fairly
regularly.  I have yet to see the small piano design incorporating a bass
bridge cantilever that would not benefit from its removal.

I hope that between Ron and I we have managed to answer your questions.

Regards,

Del




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