high or low?

[Delwin D Fandrich]

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----- Original Message -----=20
From: "David Love" <davidlovepianos@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: July 14, 2003 10:37 PM
Subject: Re: high or low?


> Not being a scale design person, but judging from observation, I would
> think high or low tension has to do with the amount of tension per =
string
> on average calculated using speaking length, string diameter and =
target
> CPS.  Looking at various scale data, it seems that on average, in the =
tenor
> and treble sections, low tension pianos come in around 150 lbs per =
string
> while high tension pianos come in around 160 - 165 lbs per string. =20

These classifications are some arbitrary. I generally divide them up as =
follows:
    Low Tension =BB 150 to 160 lbs. (68 to 73 kgf)
    Medium Tension =BB 160 to 180 lbs. (73 to 82 kgf)
    High Tension =BB 180 to 200 lbs. (82 to 90 kgf)
Note that these are averages and apply only to the unwound tenor/treble =
scaling. In most existing pianos tensions will vary all over the place =
with hills and valleys going well above and well below these numbers.

Pianos like the Steinway Model L and Model O are typical of relatively =
low tension scales. Both of these scales nearly identical scales are in =
the 125 to 145 lb (57 - 66 kgf) range in the top treble section, the 150 =
to 155 lb (68 - 70 kgf) range (the L is a bit longer and higher) in the =
low treble section, and from the 155 to 160 lb (70 - 73 kgf) range at =
the top of the tenor section down to something less than 120 lbs (54.5 =
kgf) in the Model O and something less than 130 lbs (59 kgf) in the =
Model L. The low tenor of the Model L's that I've measured are some =
longer than that of the Model O. But these were probably all N.Y. built =
instruments--my notes don't tell me if any of them were Hamburg-built =
and they may well be somewhat different.

By the way, I must assume that the figure given in the Steinway web site =
for the overall scale tension of the current Model O is incorrect. I =
doubt the plates of the recent Hamburg Model O's I have examined would =
long tolerate a scale tension of 19,000 kgf. This works out to something =
like 41,850 lbf. Even if the bass has been cleaned up this figure seems =
quite high. Our own rescale for this model (assuming original bridges, =
etc.) works out to about 37,500 lbs (17.0 kgf). Even our Killer O scale, =
complete with transition bridge, is only about 38,400 lbs (17.4 kgf). =
Given the relatively short backscale found in these instruments 19,000 =
kgf would pretty effectively tie the soundboard down and make for a =
pretty tight sound.


>
> ... Bass
> string scaling seems then to be calculated to create a smooth =
transition in
> total tension note for note through the bass.  The question as it =
pertains
> to this thread and ETD users (and scale designers for that matter) is =
how
> these differences effect inharmonicity and loudness.  Different scale
> designers seem to choose to balance the effects of tension in terms of
> loudness and inharmonicity in different ways while keeping other =
limiting
> factors in mind (such as breaking points).   =20

I can only speak for myself, but my criteria for bass scaling are (in =
order of importance):
    1)    Unison tension
    2)    Unison "power"
    3)    String inharmonicity.
If these three are balanced within acceptable ranges, string breaking =
points will take care of themselves.=20

The problem, from a scaling perspective, is found in the low tenor. In =
both of these scales the strings at the low end of the tenor bridge are =
excessively "foreshortened." From E-32/F-33 in the Model O and from =
D-30/D#-31 in the Model L the length (and the resultant string tensions) =
deviate significantly from anything resembling a log curve. This results =
in a string tension at B-27 (the last unison on the tenor bridge) of =
approximately 115 lbs (52.2 kgf) in the Model O and approximately 125 to =
130 lbs (56.8 - 59.0 kgf) in the Model L. It is possible to even out the =
string (and, of course, the unison) tensions by simply increasing the =
wire diameters of these lower strings--#20 wire in the Model L and #21 =
wire in the Model O will do it--but the result will be a significant =
spike in the inharmonicity curve. Still, this is the usual choice; go =
for smoother unison tensions (hence, more uniform acoustical power) at =
the sacrifice of inharmonicity. (Uneven inharmonicity bothers the tuner, =
uneven power bothers the pianist.)

Even in short scales like these, by using a transition bridge it is =
usually possible to blend all three parameters in such a way that string =
inharmonicity will yield a smooth, uniform tuning curve.

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