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Piano Wire, Re-Scaling and Tonal Aesthetics

By Arno Patin
Pianist and Piano Restorer, Designer and Manufacturer
We are currently witnessing a legitimate curiosity and growth of interest among the Piano trade for the benefits offered by a newly developed brand of music wire. The enhancement of tonal balance in pianos is achieved by appropriate re-scaling and stress-rate control. The purpose of this article is to share some technical background and information on this topic, in the hope that piano technicians and restorers will elevate their craft to a new level of technological sophistication and artistic satisfaction.
We are cognizant that the modern piano, in its overall design principles, has barely evolved since the synthesis established by Theodore and Henry Jr. Steinway during the sixties of the Nineteenth century (1).     
Moreover, these principles have often been applied or integrated by other manufacturers. The result in today’s piano production could be described thus: an acceptable yet outdated standard, imitated by diversely motivated and successful copycats. Even the finest European makers gave up their own aesthetical specificities as to lean towards what is believed to be the ultimate consensus.
On the other hand, thanks to the creative mind of piano technicians, and due to their quest to optimize the instruments under their care, a substantial enhancement to the piano has been implemented through numerous improvements. This is true for practically all features of the piano – for example: plate casting techniques, hammer manufacturing processes, tuning and voicing methods, and more recently action balancing and geometry control, soundboard design, scale evaluation and/or correction, and wire metallurgy.
Interestingly, most of these improvements originate from the Trade itself; while the Academia (7), in terms of acoustical research or engineering, has provided only minimal input towards possible evolutions of the piano, and while most manufacturers tend to conservatively follow the path of their historical models.
As one of the most recent elements offered to the piano history, we would like to mention the work accomplished by French designer Stephen Paulello in regards to piano wire.
Mr. Paulello is a concert pianist, former piano professor at the Conservatoire de Musique de Paris, a concert technician and a piano designer. His interest in historical French and German pianos led him to a thorough study of wire metallurgy, resulting in the creation of a line of high quality piano wire. This product features several classes of breaking load capacities and surface finishes.  
It is now manufactured to his specifications by a small independent steel company in Germany.
Physical & tonal characteristics of the Paulello wire - Purpose of Re-Scaling
It is easily noticeable, as we study the scales of most pianos, whether currently manufactured, or as candidates for re-building, that the curve shown by the break point percentage along the string plane is substantially jagged.
Let us keep in mind that we aren’t considering tensions for now, but rather the amount of effort that a string yields at one given tension. This effort, proportionally related to the breaking point of the string, is known as the ‘stress rate’, and determines the string’s acoustical efficiency.
Just inasmuch as stiffness determines inharmonicity, stress rate determines efficiency.
As an image for stress rate, let us take the example of a 1Kg (± 2Lbs) mass of whatever material sitting on the dining room table.
Should we want to push this mass a few inches forwards, using only the index finger and extending it as to push the mass, we would use most of the finger’s muscular capacity. Our index would be working at almost 100 % of its strength. Should we push the same mass with the entire arm, using the bicep, this latter would provide a sufficient amount of work at perhaps 10% of its muscular capacity. 
In both cases, we would move the mass over the same distance, yet at a different rate of muscular effort. Note that the mass remains identical, just as the string tension remains identical, as we will see below.
Since the notion of stress rate is now clarified, let us leave the dining room and get right to the facts.
We are observing here an incompatible situation: on one hand, most pianos present a very jagged stress rate curve; while on the other hand, we usually rely on wire suppliers offering only one class of stress rates. Obviously this cannot accommodate the numerous transitions or breaks encountered throughout the string scale of the pianos.
Let us take an extreme example that many of us have observed:
In a typical 6’ piano, the percentage of effort of the highest bass string, say note Bb/A# 26, exhibits ± 75% of its rupture point, (3) while its next unwrapped neighbor shows a stress rate of less than 35%, should the same wire class be used. The last bass wire is very close to both its elastic limit and rupture point. The sudden loss of efficiency of note 27 and the following unisons is perceived as a lack of definition and intensity, resulting in a tubby tone, provoking an obvious misbalance of the string plane that the skills of the best voicer cannot address.
Consequently the pianist is forced to compensate, a task s/he shouldn’t have to do, being highly detrimental to polyphonic clarity and musical expressivity.
Other areas of the piano’s string plane show similar issues whether it is the unichord / bichord transition, or the stress rate disparities present throughout the scale.
This status quo was no longer acceptable. Mr. Paulello consequently designed a series of wire presenting a progression of breaking load capacities, resulting in a palette of ‘softness’ and ‘hardness’, as thus:
For same tension, same diameter, same pitch, and same length:
‘Softer wire’ = low breaking point > higher stress rate
(Classes II & I)
‘Intermediary wire’   (Class O)
‘Harder wire’ = high breaking point > lower stress rate
(Classes M & XM)
The progression of breaking percentage from one class to the next is achieved through a precise engineering of the alloys, combined with careful and adequate wire-drawing techniques.
Needless to say, several years of research and development were necessary to engineer and manufacture the final product.
As a result of this efforts, the wire is now available in 43 gauge numbers, from .375mm [.0147”] to 1.700mm [.0669”] by 25 micron [.0010”] increments.
It is available in 5 classes, from the softest to the hardest: II, I, O, M, XM. (4)
It is noticeable that the progression from one class to the next follows the historical evolution of piano wire technology: Class II corresponds to the wire softness used in the Early-Romantic piano period, while class I corresponds to the wire manufactured during the Romantic period. Class O features similar characteristics to the famous French Firminy wire, used between 1880 and 1950, while class M corresponds to the contemporary German and American makes. Class XM is a new ultra hard wire designed for areas exhibiting high breaking risks.
However the progression of classes, while allowing accurate historical reconstitutions, finds its use in modern piano re-scaling, as an opportunity to optimize stress rate balancing, through the appropriate blending of their breaking point specificities. This leads to the process known as ‘hybrid scaling’™.
Breaking point data by class and gauge is available upon request. However, as far as rescaling is concerned, the most relevant information is the stress rate, expressed in % to the breaking point in the spreadsheet. This will be developed further below under ‘Introduction to Re-Scaling’.
As in all mechanoacoustical phenomena, there is a direct correlation between physical characteristics and tonal output in the Paulello wire.
The particular alloys, combined with the ultra-slow drawing process, allow for early pitch stability, noticeable soon after stringing.
The Paulello wire features a broader band-width, hence a wider spectrum, which can be experienced aurally or measured by any ETD. Higher amplitudes for each partial can be noted, as well as less internal damping than other wires. This is perceived by our ears as a clearer definition, a richer, deeper ‘body’, a warmer, denser color, and a longer sustain.
Innovation being constantly on the menu in Mr. Paulello’s lab, the ultimate option, the cherry-on-the-cake, is his Nickel-Plated wire.
An advanced electrolytic process prevents the metal from corrosion, and exhibits an outstanding surface finish. This Nickel-Plated wire features a very highly defined ‘contour’ of the tone, and further reduced friction, therefore enhanced sustain.
The Paulello wire is available both in Polished Steel and in Nickel-Plated surface finishes for most classes and gauges in use in the piano.
1] Henry Jr. & Th. Steinway: Patents # 26300, 26532, 97982, 127383, 170646.
2] S&S Model B
3] S&S Model M
4] Wire hardness Typogram by Stephen Paulello
5] Published by Max Matthias in ‘Steinway Service Manual’, Bochinsky 1990
6] C. Cuesta, Non-linearité de la corde vibrante, Paris VI Jussieu 1989
Introduction to Re-Scaling:
It is assumed, before re-scaling, that the entire current string plane of the instrument is plotted and implemented into the spreadsheet, as follows:
1)  Number of strings per unison
2)  Speaking length
3)  Core diameter
4)  Overall diameters, for the bass strings
5)  Copper winding diameters, for the bass strings
In the ABACUS ©, our spreadsheet dedicated to re-scaling, tensions, inharmonicity, stress rate, and intensity (loudness factor) are automatically computed, along with other data.
The suggested starting point of the re-scaling will occur right at the break between the last wound bass bi-chord and the lowest tenor blank unison.
Assuming we leave the bass scale unchanged for now, we immediately visualize the discrepancy in terms of stress rate exhibited between those two unisons.
This is where the stress rate needs to be addressed using softer wire in the low tenor, in order to match the higher bass notes.
In the original S&S scaling for model L, a hard wire is used for note 27, (whether Rőslau or Mapes, approximately equivalent to class M in terms of BP), featuring a stress rate of ± 40% to the BP, compared with the last wound note 26, featuring 75% of BP.
Should we wish to increase the stress of note 27 to a higher rate, we simply change wire class by substituting a softer class in the appropriate column.
If we choose Class O, we increase the rate to ± 50%, which is already an improvement. If we want to match the last wound bichord closer, especially in a shorter scale, we can choose Class 1, which increases the rate to ± 58 %.
Note that a break of up to ± 10% is fully acceptable, while 8 % is perceived as nearly seamless.
Assuming we are not rescaling the bass yet, we can now move up to the following unisons and look at acceptable rates in the existing scaling.
We see that they are not to be found until we reach the mid-range of the piano, (in Class M), since there is evidence that ideal rates encompass a window between 50 % and 75 % of BP (6).
We can consequently implement an intermediary softness as to match the hardness found in the upper mid-range, using Class O from the lowest tenor unison till around A49, or slightly above.
It is recommended to blend classes within the same gauge, however it is not absolutely necessary.
We can now create a smooth and balanced progression of stress rates in the entire mid-range of the piano, and address the main transition issue.
Please note that the tensions are not altered by the process, and yet they also may be balanced through the re-scaling process.
Additionally, inharmonicity is unchanged from one rate class to the other.
Ultimately, we can increase the tensions, by increasing wire diameter in the upper treble, by using a harder wire, (Class XM), in the last octave of the piano, enabling us to increase loudness while diminishing the breaking risk.
Note that we haven’t even changed any diameter so far.
As we become familiar with the basics of re-scaling, we can now move on to the bass area, which is a little trickier, and requires some special attention.
Here is how we’ll connect the dots, and divide a huge break into 4 or more minimal breaks, and reduce them to non-issues.
We have seen that variation of diameters from the original scale is rarely necessary within most of the blank string area.
Typically, we might change gauges at the transition, (should we want to lower the inharmonicity for example), or in the upper treble, as to increase tensions and loudness.
However the main tweaking of diameters occurs in the bass section.
First of all, we need to look at the stress rate of note A1.
There, a value that is lower than ± 35 % is not a desirable option. The string sounds thuddy and totally lacks energy. We can increase its rate by using a softer wire for the cores among the first unichords.
From there, we can now progressively increase tensions and stress rate among the unichords and bichords, and ultimately match the first plain unison at the transition.
We should always think of inharmonicity, tensions and loudness as ‘consequential’, and of stress rate as ‘instrumental’. In other words, stress rate should be regarded as the most significant parameter, and seen as a guideline, while the other factors can be seen as a consequence of wire diameter, length and frequency.
Also, while it may look beneficial to decrease certain diameters in the bass area, we must keep an eye on the loudness factor, which we suggest keeping at a minimal value for A0 of 155 and 175 for a 6’ and a 9’ piano respectively.
The ABACUS allows for any combinations of core/winding ratio, (provided existing steel and copper gauges are chosen), and automatically computes all specificities of wound strings, whatever ratio is chosen.
The bass calculation may appear somewhat tedious, but after a few trials it should become straightforward as well.
For comparisons, see Abacus samples available by request.
© ARNO Pianos LLC  2017/2024
Telephone  503 866 7909
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