High-tension or Low-tension?

[Delwin D Fandrich]

Gentle Readers,

In an earlier post I found myself referring to the overall scale tension as
a way of categorizing scales. An example I gave referred to a scale having
45,000 to 46,000 lb (20,400 to 20,900 kgf) scale tensions as a
'high-tension' scale. For this offence I should receive at least a slap on
the wrist though, as I think of it, something even more severe does seem in
order.... I can only plead for your mercy--especially since not one of you
has yet discovered this offence and I have willing come forward with my
confession! (And, I might add, some of you have no excuse: I've gone into
this in several of my classes and you have been there! You know who you are
but, not to fear, for your protection I'll not identify the guilty.)

The overall tension of a piano scale by itself does little to define it's
tonal characteristics. This is the sum of individual string tensions and
those can be wonderfully smooth and consistent or they can be scattered all
over a rather large ballpark. The typical piano scale--at least those based
on the scaling technology of the late 1800s and early 1900s will typically
be scattered all over that ball park. They will be up and down and back an
forth throughout the bass, often defying any kind of logic; they will
usually be quite low through the low tenor climbing up rapidly to become
high to obscenely high through the tenor; they will drop down again to some
lower figure through the upper-tenor/low-treble; finally, they will end up
quite low through the upper-treble.

Just how do you categorize a scale like this?

It is quite possible--though, perhaps, not desirable for structural
reasons--to rescale a piano having, say, 36,000 lbs (16,300 kgf) originally
and end up with a much higher overall tension, say, 40,000 lbs (18,200 kgf)
and yet give the overall piano voice the tonal characteristics of a properly
scaled piano having somewhat lower tensions.

Consider a typical small piano scale (It doesn't have to be a small piano
but these are my current interest, so pick anything below 185 cm.) having
the very common hodgepodge of tensions described above. By rescaling this
piano (and probably installing some new bridges) the bass scale is evened
out (not changing the sum of tensions all that much though usually they'll
want to go up some), the low tenor is brought up and the high peaks through
the mid-tenor are brought down (leaving the sum of tensions through the
tenor section pretty much unchanged), the low treble section will probably
be brought up some (raising the sum of tensions somewhat), and the
upper-treble will be brought up a lot (raising the sum of tensions a lot).
Now, even though the overall sum of tensions will have gone up by some 4,000
lbs (1,800 kgf) the tensions through the critical mid-tenor section have
actually dropped considerably.

The result of all of this will be a smoother, cleaner and more defined bass
section, a smoother, less noticeable bass/tenor cross-over, a more dynamic
mid-tenor and a brighter, cleaner treble section. The piano will be easier
to voice and will require less artificial hardening of its hammers through
the treble. In other words, it will be a more musical piano even though its
sum of tensions is some higher than I would like. (A nice side effect for
the tuner will be better tunability.)

I prefer to categorize stringing scales--assuming they are of reasonably
uniform tension--by looking at their average tensions through the
tenor/treble sections. By my personal definition a low tension scale is one
having individual string tensions between approximately 150 & 160 lbs (68 &
73 kgf.). A high tension scale is one having individual string tensions
above 180 to 190 lbs (82 & 86 kgf). String tensions higher than these don't
belong on pianos of any type or size. (OK, obviously, the individual string
tensions of the wrapped strings will be higher than those of the individual
plain steel strings.)

Now, just in case I don't quite have everyone confused yet, please note that
this somewhat arbitrary differentiation does not speak to scale length. When
scale length is factored in we can end up with:
    -- Short low-tension scales,
    -- Long low-tension scales,
    -- Short high-tension scales, and
    -- Long high-tension scales.
Each of these will have its own peculiar tonal characteristics and will
require its own unique soundboard/rib characteristics, soundboard loading
characteristics and hammer mass and resilience characteristics.

Regards,

Del
Delwin D Fandrich
Piano Designer & Builder
Hoquiam, Washington  USA
E.mail:  pianobuilders@olynet.com
Web Site:  www.pianobuilders.com