Designs on a grand scale

[Overs Pianos]

Hello John and all,

>I've had a look at the drawing for the 280 and it seems the lengths 
>of notes 1 to 24 are roughly as follows:
>
>  1:213.5,  2:210.8,  3:208.1,  4:205.4,  5:202.8,  6:200.2,
>  7:197.7,  8:195.2,  9:192.7, 10:190.2, 11:187.8, 12:185.4,
>13:183.1, 14:180.7, 15:178.4, 16:176.2, 17:173.9, 18:171.7,
>119:69.5, 20:167.4, 21:165.2, 22:163.1, 23:161.1, 24:159.0
>
>and that the length of the lowest trichord A-25 on the long bridge 
>is 197.0 cm.
>
>Can you confirm these figures?

While the lengths you have pulled off the drawing for the bass 
section are quite close to the real lengths, the figure for the 
lowest tri-chord is a quite a bit longer than the real figure.

>If they are right, then a No.22 wire on note 25 will come to a 
>tension of 390 lbs or so, or roughly 90% of the breaking strain. 
>The strings are extraordinarily long and that is a dangerously high 
>tension.

This would be a dangerously high tension as you say, if the length 
was actually 197 cm on note A25, which it is not. This concert grand 
has two extra bass notes, with the compass extending down to G below 
the traditional A1 (a quick look at the keyboard on the 280 line 
drawing will confirm this  - and before I get jumped on for choosing 
to extend the bass to G, I do have a reason for the choice). 
Therefore, the last note on the long bridge is actually G23. I won't 
confirm the actual speaking length at this time, but it is shorter 
than you have estimated and is strung at a percentage of breaking 
strain of around 50%. While this is higher than the percentage used 
on default concert grands with 183 cm on note F21 (36%), it should be 
reasonably safe and will improve tuning stability when compared to 
default concert grand scales such as Fazioli (278), Kawai EX, 
Steinway D and Yamaha CF.

>As for the covered strings, I have mentioned elsewhere that I never 
>design bass strings to exceed 70% of the breaking strain, for the 
>simple reason that sooner or later they will snap, and often sooner.

I agree. In fact I prefer not to go over 60%. Mind you, there does 
seem to be some variation in our calculations, which could account 
for some differences in our estimated breaking strain percentages.

>If I spin 0.15 mm (the thinnest) copper on a No. 20 core for your 
>note 24, the tension will come to about 270 lbs., 72% of the 
>breaking strain.  A 0.20 cover will produce a 304 lbs, a dangerous 
>82% of the breaking strain.  It is possible to make safe covered 
>strings for such a scale only up to note 20, and I can't think why 
>you have more than 20 covered string notes maximum on an 8'2" piano. 
>24 bass notes is what I would put on a 6'9" piano.

I've already written plenty in the past about my reasons for taking 
the cross-over higher on a number of different scales for various 
sizes of instrument. I have thought and tested my way, over many 
years, to arrive at the views I have. If you don't agree with me then 
that's just fine. I'm very happy for others to have a different view. 
The final proof for others will have to wait until the new 
instruments are out there and available for in-the-field evaluation.

>Even if we risk covering the top 4 notes on the bass bridge, we 
>still have a drop in tension when going from the lowest plain 
>trichord to the first covered bichord; a huge drop in tension where 
>every other piano I have met with has a considerable rise in 
>tension, and for good reason.  How is it possible to achieve a good 
>break with such an arrangement?

JD , your above analysis (your above two paragraphs) don't apply 
since it doesn't take account of the extra two notes in the bass. You 
seem to making quite a few presumptions, without having the full 
scaling data from which to draw conclusions. No information is 
gleanable from the drawing regarding the plain wire gauges or the 
core and cover wires for the bass section. However, I totally agree 
with your view that string tension needs to rise when we cross from 
tri-chord plains to bi-chord covers. The tension also has to rise 
again from the lowest bi-chord to the first single, or there will be 
an impedance hole at the first single strung note.

As a final comment on scaling tensions, I wouldn't trust calculated 
scale tensions for a new instrument without first testing them on a 
tension bench for safety margin, prior to building production tooling.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:ron at overspianos.com.au
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