On the topic of cello strings, part one

One of the most widely misunderstood things among string players is the measure of strings known as “tension.” People have a strong tendency to project its meaning as “tense” and other such misapplied concepts. We extrapolate from such misunderstandings things which hinder a true understanding of cause and effect regarding our instruments and their response to different technologies.

We also have an inherited tendency towards terms which in themselves are vague and misleading as we struggle to put into words what we experience as we assess things like the strings we play upon. As we are not taught a common language to address many things about our common experience as string players, it is important for us to establish a clear and science-based set of terms in order for us to have a coherent discussion of particular elements of our field. It is rare, given the competitive nature of commercial enterprises like string manufacturing (where there is a natural competitive desire for a certain degree of secrecy), to find clear statements of fact by which we can understand exactly what it is that we experience as players.

A fairly new company in England, Rostanvo, has broken somewhat with their fellow string manufacturers in publishing clearly expressed and science-based explanations of the nature of strings and their performance. As the last few years has produced some real breakthrough innovations in string manufacturing and performance, this is an exciting and useful contribution to us all.

I quote below some information from Rostanvo Strings’ website, an explanation of string tension and other factors that affect a string’s response and character. Edit: as of this writing, both their website and the company seem to be gone.

“String Tension Explained

Surprisingly, tension is easy to measure on a string (the vibrating length of the string is measured and weighed). And while it can provide us with some information on how the string will behave, it says little about how the string will actually sound.

The key variable tension can give us is an indication of is the string’s impedance. Put simply, impedance tells us how much energy the string can carry and relay onto the instrument. The higher the tension, the larger impedance, resulting in a louder sound.

But it does not tell us anything about the string’s frequency output, ie the instrument’s quality or timbre of sound.

A Cello’s changing shape with strings

Admittedly, the cello body’s shape does change slightly when there are no strings attached to when strings are tuned onto the instrument. But the impact to the shape between high and medium tension strings is too slight to have any noticeable change. If you don’t believe us, there’s a very simple experiment you can perform to prove this to yourselves. Read our article on “string tension proved” for instructions.

But tension can still be a useful measure from a player’s perspective. High tension strings, because of the greater levels of impedance, need more energy given by the player in order make them sound. They are more power hungry and can sound louder. But they are also harder to control ,especially at lower volumes. No surprise then that “soloist” strings tend to have higher tensions (as more skill is required to play them).

Higher tension strings however have one key advantage aside from sounding louder. They maintain their intonation more easily at a range of pressure levels. Take the C string for instance. Try playing the same note with light and then heavy bow pressures. The pitch should rise. This is particularly pronounced on low tension strings while the higher tension equivalent will maintain its pitch much better.

So to conclude, be wary of focusing too much on string tension. It is the easiest piece of “technical information” you can get on strings, so easy you can calculate it yourself. But sound wise, there are other factors which merit more thought.

String stiffness and flexibility

As we have already mentioned in our introductory article, variations in the waves formed on a string are what makes one string sound different to another. And as you might expect, the stiffness of a string will affect the wave and thus the way energy transmits to the rest of the instrument. If perfectly stiff and rigid, no wave motion is generated which means the string won’t sound at all. You absolutely must have some flexibility.

From a sound perspective, the reason all this matters is because it has been shown that changes in the bending stiffness of a string impact the balance of harmonic and inharmonic frequencies. Ie stiffness influences the frequency output and by doing so, changes our perception of whether the string is warm, metallic or dull, or any other idiom we wish to assign the frequency pattern we hear. Specifically, the stiffer the string, the less prominent the higher harmonics.

So stiffness would be a hugely useful variable when comparing strings. But there’s a catch – measuring it is not as easy as determining the string’s tension. You need specialist equipment to get accurate readings. And even if you had it you would need to standardise the bowing motion applied so that readings are consistent. Even the bow and rosin used would affect the results. So unfortunately we need to resign ourselves to the fact we aren’t going to get this information from manufacturers soon. A pity, as it would be a lot more useful from an acoustic point of view than tension.

What your string is made of

When choosing strings, one of the most obvious questions you’ll be faced with is what material you want the string to be made out of. The reason materials matter is because each will be different in terms of elasticity, stiffness and weight/density, and thus influence how waves travel through the string.

As we mentioned in our first article, the shape, speed and pattern of these waves is what differentiates the sound between different strings. And so it makes sense that different materials will influence how those waves move through the string and thus impact the sound we hear.

Unless you’re a historical performer and are buying gut strings, you’re likely considering a synthetic core or a steel core, wound with different kinds of metals such as tungsten, steel, aluminium or silver. The windings can themselves be plated in other metals such as chrome or gold.

Understanding precisely how these different materials might impact the sound is a hugely complicated subject. Something a professional material scientist would be better placed to attempt to explain. But to give you feel for what can change, the introduction of tungsten winding is a good example.

Different metals have varying densities. Tungsten is almost twice as dense as silver, meaning that half as much can be used in order to maintain the same overall string weight and thus tension. Tungsten strings are thus thinner, and thinner strings generally have less stiffness, which from an acoustic point of view means a greater harmonic content. From a playing perspective thinner strings are also easier on your fingers and can have a quicker response from the bow.

Materials and practical considerations

The elasticity of the string refers to how much the tension (and so the pitch) changes when you tighten or loosen your string. Steel core strings are approximately three times more elastic than a synthetic string, which means that steel strings may be slightly more difficult to tune (since the tension responds rapidly to small changes at the peg or fine tuners).

However, steel strings are a bit more stable than synthetic core strings; just a few minutes after putting them on to your instrument for the first time, they’ll settle into their stable pitch, while a synthetic core string might require several hours to settle (and gut strings far longer).

Materials also react in different ways to the environment they are in. Heat and changes in humidity effect steel core strings less compared to synthetic and gut. So keep in mind even the moisture from your hands and fingers, and moving between dressing room and auditorium can have an impact.”