Designs on a grand scale

[Horace Greeley]

At 11:02 PM 10/7/2006, you wrote:
>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
>_______________________
>
>Web http://overspianos.com.au
>mailto:ron at overspianos.com.au
>_______________________


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Horace Greeley
Systems Group
Controller's Office
Stanford University

651 Serra St., RM 100
Stanford, CA 94305

voice:  650.725.9062
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