Wound strings

The string sound

Harpsichord makers and players are always looking for the ideal string material with thebest sound. People speak about emphatic fundamental or about rich and bright sound with dominant partials. They speak about great brilliance, excellent sonority, tonal clearance, easy touch and strong continous vibrating. For this again and again there are sporadically new theories which make the ideal sound dependent on only one factor. On the other hand there are many people who loose their curiosity because of so many complex implications.

We don’t want to give fast and simple answers, but we would like to try to explain different physical parameters and their influence, so that musicians and instrument makers can make a certain choice for strings.

Of course people with a clear sound ideal can divide easily a sound in lovely and ugly. All ideals, also outside of the music, have got this duty. But those who want to keep their freedom and want to experiment, will need all information about the available material.
The following text should give a basic knowledge about string materials to make the decision easier. First of all is naturally that the string should not break. Harpsichord strings are available in a big spectrum of tear resistance.

The tear resistance (Rm) is dependent on:
• the type of material (iron, brass, copper, ...)
• the alloy within a type of material (CuZn28, CuZn15, ...)
• the way of production (diametre reduction, intermediate annealing, surface quality, ...)

There is no big problem to determine the tear resistance technically. Unfortunately it tells us only something about the point where it is already too late and the string is broken. In the practice there will be made a security subtraction of eg. 20% or one tone below the tearing limit. Of course these are arbitrary assumptions and also years of experiences are of no use if the new bought material does not have the absolutely same physical properties as that material used before.

That‘s why we invested much time and money in the string testing. You receive a detailed test report (without surcharge) to the string roles we deliver. The test report includes eg. the load deflection curve and practical hints for using the material.


The tearing test

For creating the test-report the wire will be fixed in the testing machine. Therefore we have got a load measuring device for the thin and weak wires with a maximum load of 200 N. For the strong wires we have got a load measuring device of 5000 N. So we receive exact measuring results both in the lower and upper part.

The measurement of the wire stretching is more difficult. For measuring the elongation we need an always equal long testlength and the lenghtening has to be measured in a thousandth of a mm. For this we have got an extensiometer with an exactly defined measuring length (L) of 50 mm. With this equipment we can determine the exact change of length (àLt) without faking the test results because of sliding in the wire clamps or because of swaying of the test lenghts.

For compensating the normal wire curvature we work with a small preload. The preload is included at the load measuring device and flows into the calculation of the drawing force. So the beginning of the diagramm of the load deflection curve printout is placed higher to the preload. So the beginning of the curve looks smoother but this does not have an influence on the measured datas.

Only because of the optimized test arrangement of the measuring of thin wires it is possible to make statements about the maximum drawing force (Fm), the different elastic limits (Rr0,01, Rr0,03, Rp0,2) and the coherent results like modulus of elasticity (E) and spring stiffness.


The test report

For understanding the technical terms we would like to refer to the glossary on the test report.

The results breaking limit, ultimate strength, elastic limit and recommendations are shown on the test report as well as tension in N/mm2 and in the measured N as in percent (%) referring to the breaking limit. This triple information allows an immediate understanding without converting.

The tension values (N/mm2) are interesting because you can compare different diameters with each other. With the information of loads (N) you can arrange the limits on the diagramm. If you read the values at the scale on the left side of the diagram and if you search the crosspoint which is on the same hight on the curve, you get an optical impression of the position of the whole curve. For judging about the often used safty deduction one can use the percent values referring to the breaking limit. This tripple value listing allows an immediately understanding without conversion.

But how do we find the values which are printed out on the test-report? At first we measure and store the changes of the length and load deflection during the tensile test. This amounts the printed out diagram curve.

There are different types of stretchings on the measured extension of the wire up to the breaking point. You can differ between reversible and irrerversible extension or like the standardisation says between elastic (àLe) and non-proportional extension (àLp).

If you only load the wire a little and then reduce the load, the wire gets back its original length. So the material has only been stressed within the elastic elongation. You can compare this with an aircraft wing or with a car which has the same shape after using it without accident like in the beginning.

If the load rises over the elasticity limit, there is a permanent deformation ( r) after the reduction of the load. According to our comparison with the car this would be a dent. If you drive a car which has a small dent there are elastic and plastic deformations (àLt) at the same time. But there is no more normal use possible if the dent is really big.

The standardisation defines the elasticity limit where the non-proportional lengthening reaches 0,01% of the test length. In our test arrangement with a test length of 50 mm in the extensiometer this corresponds to a plastic deformation of 0,005 mm.

For the determination of the different stretch limits on the load deflection curve first we have to place a parallel to the beginning of the diagram. We define the beginning of these parallel at 20% and the end at 40% of the maximum load. We could put the limits also lower and more narrow. At lower placed values the smallest inaccuracies can lead to extrem variations.

We intentional choosed an interval, so that we can test all materials which are used in the harpsichord manufacturing with the same adjustment. Because of this we have got the possibility to reach an optimized comparison of the test results.

The so defined parallel shows a certain gradient in the load and length deflection curve which is used for calculating the stiffness or the spring stiffness constant. If you transfer the parallel on until the sample is elongated by 1mm, you receive the spring stiffenss constant in N/mm. As the load is very dependent to the diametre of the sample, you can compare different materials only with the same diametre. The spring stiffness constant flows into the calculating of the inharmonicity.

The modulus of elasticity is a material index which describes the tension of an elongation of the measuring length by 100% (spring stiffness constant x measuring length / sample cross section). The elacity modulus is needed in the calculation of the scaling. As it concerns of a load per cross section (tension) it is possible to compare the different diametres with each other. At the same time you find out that the elasticity modulus is dependent on the alloy and also on the cold forming while drawing the wire of the material.

For defining the 0,01%-elastic limit the parallel line is moved by 0,005mm to the right. The point of intersection is the elastic limit.

Exactly that way you define the 0,2%-ultimate strength (Rp0,2), but the parallel has to be moved by 0,1mm to the right in the diagramm. As the percent values of the non proportional elongation ( p) refers to a measuring length of 50mm, these are the measured elongations of 0,005 and 0,1mm on our diagram.

Cold formed string wires do not have a yield point with afterwards yielding area. That‘s why this cannot be defined. On materials without yield point we calculate the 0,2%-ultimate strength alternatively. We think that this is too rough for the practical use in the harpsichord manufacturing. On the other hand we think that the elastic limit is too exact. So we have determined an additional limit (Rr0,03) which we defined at 0,03% plastic deformation. We call this the recommended maximum load on the diagramm.

Of course this can be only a reference value which can be passed or fallen short in practice. For to make comparing different tests of different materials more easy, we have choosen the same limit for these recommendations for all materials.

For the practical view on the test report, we have converted the four different limits also into scaling lenghts for c2 at a pitch of a1 = 415 Hz and 440 Hz.


Historical Practice

Do we need such test results about the string material in the historical harpichord making?

In former times the harpsichord makers did also not have string tests at their disposal.

We do not know how big the selection of string wires for the former harsichord makers have been. Certainly the business in Europe with such specialities like fine wire was bigger than we can imagine. It is another question wether the individual of the instrument maker had access to the wire and wether he could afford the wire everytime. Principally the scaling was made to the requested pitch and to the available string material.

This is exactly the opposite we are doing today if we work on a historical model. We adopt a scaling although we do not have much information about the used string material.

So the harpsichord maker of today asks himself which material he can use for the original scaling. The same question arises at all restorings even if a musician wants to change only one string.


The calculation of scaling

Today we know the tensile strength (Rm) because of our test-report. So we can calculate wether the wire will be stabil on a certain scaling.

The vibrating string length between the bridges (length) is dependent to: frequency, diametre, gravity, drawing force, specific weight

l = 1 / (n x d) x ­(g x p / x s)

length = 1 / (frecuency x diametre) x root of (gravity x load / x specific weight)

If you take out the gravity and as constant with which you calculate the diametre and put in 17841 for it, the formula looks like this:

length = ( 17841 / frecuency x diametre) x root of (load / specific weight)

So if three items: frequency, tension and length on two strings one factor is equal and one is unequal, the third factor has to be unequal as well, for example: at equal frequency and unequal lengths of two strings the tension is unequal, too.

If the load of a string is near up to breaking limit, the string will be continous elongatied by the constant overload so it has to be compensated by tuning again. During the time the string gets more and more thinner and weaker until it breaks. This can also happen after one year or later. One shouldn‘t forget that the stress on the string is not spreaded equal because of the friction at the bridge pins. The bigger the bend is on the bridge pin the bigger is the friction, and the bigger must be the reserver on the wire.



The wire choice

The differences between the several materials which are used in the harpsichord making are enormous. So a weak copper string in the bass can have a tensile strength of 500 N/mm2, and a thin and long string in the discant can have 2000 N/mm2.



Which material should I choose for my scaling?

If the scaling is already given, as it is usually today, you have to carry out a calculation of scaling cogently. So one can say which tension the material has to stand and one can choose a material on which the calculated tension is below the ultimate strength. As help to find a direction one can also use the recommended maximum tension on the test report.

Because of this calculation one can have the certainty that the string does not tear under unfavourable conditions. At the same time one can compare the different materials with each other and get a feeling for typical material typical profiles.

It becomes evident that one can only choose the correct material if there are different materials on your disposal and if one knows their properties really exactly. The reference values given by producers have big tolerances and are of no use for this, as the actual physical wire diametres can deviate extremly from the reference values.



Short historical aspects of the wire drawing

Metallic music strings from iron, copper or silver wire were already in use since the 14th century in Europe. Brass and golden wires were added until the 18th century. Only after 1834 there were also the high sounded steel strings.

The early strings did not have such a high tensile strength as it is possible with today‘s materials. This is conditional on variations in the alloy through different ores and in the soilings trough dross, and even through the later adaption through forging.

The wire was drawed on handlreels in the always same direction, so that the structure of the wire could not tear open despite soilings.

In the modern wire production the material first will be rolled. In the rough draw the diametre will be reduced from 12 to 3 mm, in the medium draw there is a further reduction to 1 mm to come to the fine draw for bringing the wire to very thin diametres. On drawing the wires through a conical drawtool, the several cristals will be stretched and moved mutually. At the same time they are turning with their sliding directions in to the deformation direction. Turn, rigidity and adjustment of the cristallic structure are in close connection with the material direction. Through rationalizing the production process like through big cross section decreasing of the wire and draw stones with big draw angels, the material direction will be more inhomogen again.

So it is very interesting to see how people manufactured a good product under the observing of some rules in former times. On the other hand we know that there cannot be produced the best quality though enormous technical knowledge because of the cost-pressure today.



Osemund iron

The term Osemund probably comes from the Scandinavien Osemund-furnace. In the course of history the term was used for different iron qualities and to the belonged production procedures.

The iron which was won of the Osemund-furnace was directly forgeable and could be compared with the poorly carbon iron of the furnace. Historians in the 19th century pointed out that this iron was not brittle in spite of the high phosphorus concentration. There were also described procedures how the Osemund iron could be carburised to steel.

In the 13th century the continous furnace = “flow”-furnace become more and more common. People had rough high carbon iron and the problem was to decarborize it and to make it forgeable. This was necessary when people wanted to use it the same way how they were used to use the Osemund iron from the previous furnace. The procedure called „Osemundfrischen“ should have served to it.

Osemund became more and more to an especially qualitative mould of carbon poor iron because this did not came up automatically through the new “flow”-furnace.

At least the terms Osemund iron rispectively Osemund steel were used for materials that were assembled with sandwich technique. Here the carbon rich and carbon poor deposits were forged and folded together. The silicate inclusions in the poor carbon iron made special effects in the mechanic.



Phosphorus

As already mentioned there are indications from the 19th century of the relatively high phosphorus concentration in the Osemund iron. Also new analysis in the USA point to this.

On own material analysis at the „Bundesanstalt für Materialforschung“ we locked that also modern piano strings have got an extremly high phosphorus concentration. Of course this could not be as phosphorus and sulphur are regarded as steel damager which make it brittle. A demand showed that it is not possible to distinguish between surface and core because of the modern fluorescence measuring method.

So the piano string wire only had a phosphated surface for the protection against oxidation. We do not know how the analysis in the USA were made out.

To this point it woud be good to know something about historical wire production. After several drawings the wire had to be softed again by annealing. This was necessary because people hadn‘t had hard metal or diamants as drawing stone. The so called „Hol“ was only a little harder as the material which had to be drawn.

After annealing the wire had to be descaled. For this each of the wire drawers of a „Drahtrolle“ (= means workshop for producing the wire)brought the collected urine from the whole family in a bucket every morning. The wire was pickled in the urine for descaling. As urine contains much phosphorus it is conceivable that the material adds itselve with this. Especially the urine of children contains much phosphorus and was collected in the children rich families. It is told that the workers took home rape oil, which was used for drawing in the evening, in the same bucket for roasting potatoes.

So it could be asked wether the described slight enrichment with phosphorus is in touch with the production procedure and also why the phosphorus does not do its harmful effect in the Osemund iron. Perhaps the phosphorus concentration was only increased on the the outside layer gets to the inside. But this is probably not in the same way as it phosphorus is distributed in the structure.



Stringdiametre and elongation coefficient

Remy Gug shows in his analysis to the Nuremberg wire numbering that the wire diametres were defined through weight and length in former times as people hadn‘t had the micrometer as we.

People knew the „Drahtklinke“ which was for testing but not a measuring instrument. On the other one shouldn‘t forget the weight and length units at that times haven‘t been standarised.

Gug described this procedure how the wire drawer had to reach a certain given wire length per weight unit. If a wire will be reduced halven in the diametre it will become four times longer. Of course the wire length is easier to mesure than the diametre of the wire. The wire swifts with defined extent were well known. The wire which should be measured was drawn over it. Also „Zängelmaße“ are described. This is a piece of sheet metal which was cutted slanting at the upper border and which had four marks. If the wire lengthend from the first to the fourth mark one diameter reduction step was reached, for example: if a wire drawer would draw a certain weight unit to eg. 100m length and he missed it by 2,5%, that means 102,5m instead of 100m, this corresponds to a diametre flaw of 0,005 mm at the diametre 0,2 mm. The elongation could be defined in advance with only a small sample with the „Zängelmaß“. The „Zängelmaß“ had 48,8 mm (2 inch). If the wire drawer made the described flaw of 2,5% the length was 1,22 mm. This is a flawsize which could be seen with the „Zängelmaß“ without any problem.

In former times it was quite possible to reach exact diameter steps. Through the procedure with the „Zängelmaß“ there are also constant diametre reductions with constant reduction coefficients.

In our time the question is if the wire diametres should be produced in a metric system eg. 0,20 mm, 0,225 mm, etc. or if it is more important to have a regular diametre reduction for the instrument building or the scaling interpretation.

We have decided for the Nuremberg system how it was demanded from Remy Gug. It is not decisive if the numbering made of him is historical correct, but that the diametre reduction runs over the whole range in 5,313 % steps. With this a fine and regular diametre transition is possible, what would not be able with a metric gradiation.



String order

The best way is to order the wished strings through giving the article numbers which you can find in the catalogue. If you cannot dertermine them certainly, we offer some services (see further below).



Exchange of wrong ordered strings

Please see that we cannot exchange wrong ordered strings. This is because of the rust protection of the next customer. Nobody wants to get started on string roles or string material which oxidizes because it was stocked too moisty and it was touched with inprotected fingers.



String prices

The string prices in our catalogue are including the enclosed test report except for Röslau-piano string wire. Also all replacement string will be delivered without a test report.

As string and scaling determinations are complex, no surcharge for consultation is included to the material price. Services for choosing the correct strings are offered separatly.



Order for replacement strings

If you cannot make sufficient information about the required material, we offer the following possibilities:

A. Calculation of one replacement strings
B. Calculation of further replacement strings

Therefore we need the following information:
- tone
- vibrationing length of the string (between the bridge pins)
- pitch
- Ø of the string or of the both neighboured strings
- string sample if you cannot give the diametre
- type and manufacturer of the instrument

Alternatively we can carry out a tearing test with a long enough piece of the teared string. Among other things the break- and elasticity-limit and the ultimate strength will be measured.

With these information it is possible to estimate which material you should require.



Order of scaling calculations

If an instrument should be completely restringed we also offer the calculation of scalings. If several materials are technically possible you receive different scaling suggestions. If wished we also deliver the scaling calculatons with commentary to the suggestions. In case you have got the necessary expert knowledge and the technical requirements, you can also download the scaling calculation programm called „Mensurix“ from the internet as shareware (http://www.piano-stopper.de).


Putting on Spare Strings

1. Turn out the wrestpin with approximately 5 turns counter-clockwise.

2. If possible, always wear thin tricot gloves when working with strings.

3. Take the string out of the packaging and undo the knots.

4. Unroll the whole string.

5. Try to avoid loops and kinks! In case a loop should tighten, the string is likely to tear in that place.

6. Fasten the already looped end to the free pin on the hitch-pin rail.

7. Lead the string wire between the jacks to the free wrestpin.

8. Cut the string, about three fingers' breadth behind the wrestpin.

9. Thread the string into the pin's hole and turn the wrestpin with one hand clockwise.

10. When turning, let the other hand keep the string slightly stretched, so that it cannot come off neither from the hitch-pin nor from the wrestpin.

11. Pay attention to the windings on the wrestpin: they must be lying one beneath another, not over or upon another.

12. Brass and copper strings should "rest" a semitone lower. After one hour, draw them carefully up to the final pitch.

13. Iron strings take about one week to develop the full timbre, non-ferrous metals need one to two months.


TIPS FOR STRING STORAGE
Stringmaterial rusts if the stockage and the handling is wrong.


Stockage

The wire should be stored with less then 40 % humidity so no rust or corrosion can arise from this dry climate. If the stockage cannot be done with this climate, you can manage with antirust paper and Climagel. The oxidation will be only slowed down from these antirust agents but cannot be stopped totally. An optimized stockage is in a steam impermeable bag with a humidity under 40 %.



Handling

You should always were gloves from e.g. tissue or latex if you touch or put on strings so that neither sweat nor its acid gets on the strings. Sweat speeds up the corrosion process and makes the strings brittle. If your hands sweat fast you should always have a look to dry gloves. We recommand the gloves from latex as no wetness gets trough them.



Climagel

Climagel is a silicate. It takes humidity until the silicates are saturated and caped. That’s why the Climagel allows a relative rust protection. When Climagel is saturated a reactivation is possible by drying it in the oven at approx. 150° C for 15 minutes.



Antirust paper

The antirust paper protects metall surfaces not only on contact. It also protects through a gas phase on distance (effective on both sides). It always emits very small quantities of antirust gases which preserve the pack good reliable (limited in time).



Aluminium laminated bags

In contrast to common PP-bags the aluminium laminated bag is not only waterproof but also steam impermeable. Combined with vacuum the packed in material is protected against rust and corrosion as no or only very small quantities of air is existing.



Stockage of the string material

Each string role is packed in an antirust paper. Together with a bag of Climagel it is vacuum-packed and shrink-wrapped in a aluminium laminated bag. Additional it is packed in a further transparent PP-bag with the correct tearing-test, so that the material can be identified.

With the tearing-test you can find out before opening the aluminium laminated bag if the correct string material is in the opaque bag. Unfortunately we cannot take back the stringmaterial after the bag has been opened, as the material coul already be used or could be handled wrong. The cut off aluminium laminated bag does not offer a 100-% rust protection. You can pack the role together with the Climagel and the antirust paper and stock in the aluminium laminated bag. This offers a higher protection against rust and corrosion as if the string material would be stocked open. After the Climagel is saturated it is possible to reactivate it as described.