More than you ever wanted to know about strings – Part 2

In this final part of my two part feature on those vital generators of tone, guitar strings I take a look at how to fit strings correctly, at why strings break and examine long life and classical or ‘nylon’ strings in more detail.

An associated table lists most of the string brands available worldwide and the types of string made under each brand. Typical string set prices, for each brand, are compared in a bar graph.

String elasticity and ‘stretching in’

A material behaves elastically when it returns to its original size after being stretched.
String elasticity is a property that seems to be widely misunderstood. There is a belief that new steel strings permanently elongate before they settle down and can be relied upon to tune to a stable pitch. It is even commonly recommended that this supposed stretching-in can, and should be accelerated, by grabbing the string somewhere around its middle and forcibly yanking it away from the guitar. This is an unnecessarily violent thing to do and can damage both the string and the guitar. It may result in a permanent kink in the string by flexing it beyond its elastic limit. Once this happens, the strings harmonic purity is compromised, even though the kink may seem to disappear when the string is tuned to pitch. Pulling on the strings can cause the ball ends to bite hard into the bridge plate, accelerating wear in this area. Any tuning instability for a new string is not due to permanent elongation, but to settling and slippage at the bridge and tuners. Careful and correct installation of new strings will minimise and even eliminate this movement.

Why strings break

When increasing tension is applied to a string, first it deforms elastically, then, as tension is further increased, it goes into plastic deformation and eventually, with only a little extra tension, the string breaks.

A properly designed and properly made string, under normal tuning tension, should be operating well within its elastic area. It should act like a spring, and therefore be a long way from its breaking point. However when strings are bent through sharp angles, for example at the tuners, or at the saddle, local tension at the bend point is greatly increased. This is because the material of the string, at the outside of the bend, is tensioned or stretched, purely due to the bending action. Once the string has been bent far enough around a sharp angle for the bend to be permanent once the bending force is removed, then the material of the string, on the outside of the bend, has already exceeded its elastic limit and is in plastic deformation. Any permanent bend in a string means that the string is relatively close to breaking. This explains why, when stings do break, the break point is almost always either at the saddle or at the tuner, where the sharpest bends occur.

Diagram of plastic deformation of a string at the saddle

On electric guitars, with metal saddles and sometimes metal nuts, any roughness in the metal can act like a saw and contribute to string breaking by wearing its way through the string. On acoustic guitars, with their plastic or bone saddles and nuts, this is less likely to happen. Any rough, sharp edges on tuner post holes can be a problem and should be smoothed away. Locking tuners are starting to appear on acoustic guitars and sharp points in the locking mechanism itself can also cause strings to break.

Fitting new strings

Most acoustic steel strung guitars are fitted with a pin bridge. This type of bridge has six tapered holes that pass through the bridge, through the soundboard under the bridge and finally through the bridge plate. The ball ends of the strings are passed through the holes and the bridge pins are inserted to block the holes and stop the end of the string slipping out. Bridge pins usually have a groove cut along their length which should allow clearance for the string. Tensioned strings aren’t held in place so much by the pins, but by the ball end of the string being pulled hard up against the bridge plate by the string tension.

The bridge plate, a hardwood plate glued to the underside of the soundboard under the bridge, has two functions; it provides a hard surface for the ball ends to seat against and it stiffens the soundboard area immediately around the bridge. Without the plate the ball ends would bite into the soft wood of the soundboard. On guitars that have seen a lot of use the ball ends sometimes do wear through the bridge plate and the soundboard and wind up against the underside of the bridge. When this happens, string tension tends to start tearing the bridge away from the soundboard.

With a properly made pin bridge, each string should slide quite freely through the groove in each pin, even when the bridge pin is firmly wedged into its hole, and lodge firmly up against the bridge plate. There are two ways this can go wrong; either the ball end can get caught on the end of the pin and will tend to pull the pin up out of its hole as string tension is applied, or there isn’t enough clearance for the string in the pin groove and the last few centimetres of the string, where the twist lock for the ball end starts, get jammed between the pin and the sides of the bridge hole. This can lead to gradual tuning instability as the string is slowly pulled tighter into the gap between the pin and its hole. This should be avoided because a jammed string can be extremely difficult to remove. Filing a bevel onthe end of each of the pins will stop the ball ends catching and lifting the pins.

Fitting a string

When installing a new string first drop 3 or 4 centimetres of the ball end of the string into the bridge pin hole. Then push the pin into the hole making sure that the groove in the pin lines up with the string and is also facing the saddle. Once the pin is firmly seated in its hole, grasp the string carefully near the pin and pull it upwards until it feels that the ball end has settled against the bridge plate (it’s usually necessary to hold the pin down with a fingertip). Thread the other end of the string through the hole in the appropriate tuner post. Leave about 3 centimetres of slack in the string and start tightening the tuner while guiding the string, for a smooth wind onto the post, with a finger. Check that the string ball end is still up against the bridge plate and hasn’t slipped down inside the guitar before you start winding.
If the bridge pins fit properly, the tuners and nut are in good condition and the rest of the guitar is structurally solid, correctly installed new strings should come up to tune almost immediately and remain stable.

Strings & tuning machines

There are a number of recommended methods for stopping strings slipping at the tuners. These are all ways of ‘knotting’ the strings around the tuning posts. What’s not generally realised is that most tuners have posts designed to lock the string, providing the string is properly installed. The tuner posts taper towards the hole through the post. If the string is positioned to allow enough slack for two or three turns around the post and then wound on evenly, with the turns laid flat below the hole, the taper forces those turns to slide up and jam up against the length of string running through the post hole. This works very well on all of the wound strings, but plain strings may benefit from having the end of the string looped twice through the post holes.

This close up of a normal tuner string post shows the loops of the string around the post being forced up to lock against the end of the string by the taper on the post.

Long-life strings

One of the things that make’s the guitar such an expressive instrument is that both hands of the musician are in intimate contact with the primary sound generator – the strings. Unfortunately this contact is the main reason that guitar strings must be changed so frequently. Guitar strings are not worn out by vibrating and producing sound. Piano strings, which are made of the same materials as guitar strings, last for many years, regardless of how often, or how loudly, the piano is played. Guitar strings wear out mainly because of corrosion due to dirt and moisture from the player’s hands. The introduction of salt and water from the fingers to the gaps between the core and the wrap wire causes an electrochemical reaction to occur, resulting in accelerated corrosion. If wound strings were made of electrochemically neutral materials then this wouldn’t happen and the string would last much longer.

It took an outsider to introduce the concept of long-life strings, which is not naturally a concept that is in the string maker’s interest. W. L. Gore & Associates started out in 1958 as company that specialized in developing and manufacturing fluropolymer coated wires and cables. They went on to develop the permeable, but waterproof textiles, known as Gore-tex, before going into the musical instrument string business in 1997. Gore’s Elixir strings were the first strings to feature a polymer sheath to guard against dirt and sweat. Unlike all other long-life strings the Elixir wound strings have their protective barrier layer around the outside of the string, while the rest of the construction is identical to a conventional wound string, with a hex wire steel core wrapped in a bronze or phosphor bronze winding (nickel in the case of the electric strings).

Most of the companies making long life strings have approached this problem by introducing a neutral coating to act as a barrier, to otherwise conventional strings. A few companies have adopted alternative processes, such as metal plating or cryogenic treatments. Each company is almost forced to adopt an approach that is in some way unique because of patent protection. For example D’Addario’s EXP range of strings uses a hard chemical coating applied to the wrap wire before winding while DR Strings use coloured polymer plastic coatings on the wrap wire.

One of the most radical approaches has been taken by another newcomer to string manufacturing, the American company Rohrbacher (www.rohrtech.com). By changing their wound string cores from Swedish steel to titanium, wound with nickel wrap wire and using a stainless steel wire for their plain strings, they have almost eliminated electrochemical corrosion from their strings. They say that they have string sets still in use, and in perfectly good playing condition, that were installed when the company started making strings in 2003.

At first all long-life coated strings only had treatments applied to the wound strings in a set and the plain strings were identical to those in an untreated set. A very recent development is to apply an anti-corrosion treatment to the plain strings as well. Most string companies have turned to other companies, expert in anti-corrosion coatings, to advise and develop coatings for their strings.

All long life strings sound a little different to an equivalent untreated string. New long life strings are usually not as bright as normal new strings, but the big advantage is that the long life strings retain their initial tone for approximately three to five times longer than untreated strings. Long-life strings have become very popular with acoustic guitar makers because a new guitar can survive a month or so in a retail store without its strings going dead. They are a real boon to musicians touring with several guitars since they drastically reduce the number of string changes required.

In general with coated strings the thicker and softer the protective coating the more it damps the brightness of the strings and the quicker the coating wears off. Also, with the thicker coatings, the less the coated strings look and feel like un-coated strings. Cleartone strings, the most recent long-life coated strings to come onto the market, claim to feature the thinnest (only 1 Micron thick) and toughest, protective coating available. Both Cleartone wound and plain strings receive the same coating treatment.

String companies compensate for their possible loss of income on sales of ordinary strings by charging more for long life strings, although the manufacturing cost increase is probably quite small.

Cryogenic hardening

Cryogenic hardening is a toughening treatment for metals that was developed in the 1990s. The crystalline microstructure of various materials is altered by slowly cooling them down to around -195 degrees, keeping them at that temperature for a controlled period and then gradually warming them back to room temperature. In steels, large crystals of relatively soft austenite are converted into smaller crystals of harder martensite. This process also heals micro-cracks and imperfections in the metal surface, making it smoother and less prone to stress fractures. Some string makers, in particular Dean Markley, process their strings in this way and claim improvements in longevity and tone.

Cryogenically treated non-ferrous metals and plastics also benefit, becoming tougher with a smoother surface because the treatment realigns randomly oriented molecules so the material has a more regular microstructure.

Nylon strings

Nylon strings were adopted as a substitute for gut strings due to a shortage of gut after the Second World War. They are in almost universal use now, because they are more consistent than gut and far less affected by temperature and humidity, although some still regard gut strings as the benchmark for tone.

The story goes that Segovia was touring the USA and happened to mention at a function he was attending that he was very short of strings particularly the top string. A friend of the DuPont family heard his comments and obtained some lengths of DuPont Chemicals mono-filament nylon line which he gave to Segovia. Segovia thought the nylon line worked quite well as a replacement top string and later asked Albert Augustine to work with him to develop a full set of nylon based strings. After several years of work Mr Augustine eventually succeeded in making a full set of nylon based strings that Segovia was happy with, and today Albert Augustine Ltd. are still making high quality nylon strings. E & O Mori (laBella strings) also claim to have worked closely with DuPont to produce the first nylon strings.

Nylon or ‘classical’ strings and string sets aren’t normally sold by gauge like steel strings, but by tension (just to be different Dean Markley list the diameters of their classical strings). The early nylon string sets where available in only one type or tension, but now nylon string sets are sold in as many as six different tensions. Hannabach, a company with perhaps the highest reputation as a maker of classical guitar and orchestral strings, makes sets in super low tension, low tension, medium tension, medium high tension, high tension and super high tension. However two of these sets are semi-hybrids, the Super High Tension and the High Tension sets have the same trebles, but the basses of the High Tension set are lighter and similarly the Medium and low tension sets have the same trebles, but the basses of the Low Tension are lighter. These distinctions between the various type and tensions of ‘nylon’ or ‘classical’ guitar strings are not usually that obvious from looking at the maker’s catalogues or string packets.

Individual tensions for nylon strings are below 20 lbs and total set tensions vary between around 80 lbs for low tension and 100 lbs for super high tension (approximately 45 Dekanewtons in IS units of tension), half that of a steel strung guitar. Although not as extreme as the tension variations found in steel string sets, the tensions for nylon string sets are still far from even.

This graph plots the six tensions of nylon strings from the renowned Hannabach brand. Dotted lines are used for the High Tension and Low Tension sets so that it’s clear that their plain strings are the same tension as those in the Super High and Medium sets respectively.

The standard method of attaching nylon strings at the bridge is to tie them on by passing the string through a hole in the tie block just behind the saddle, then looping the end of the string under and through in a simple friction-twist knot. In recent year string companies have introduced ball end nylon strings that are simpler and quicker to install and are not prone to slippage.

The myth of carbon fibre strings

Although it is extremely difficult to get detailed information about ‘classical’ strings, carbon fibre strings seem to be a myth. Savarez make KF composite trebles for their Alliance range of strings. Although Savarez aren’t explicit about the construction of these strings, and they are sometimes referred to as ‘carbon’, they certainly don’t appear to be made of carbon fibre.

Plain nylon strings are now available in several types; normal plains, rectified nylon and so called carbon. The normal plains are clear, smooth and shiny and are left in the state that they emerge from the extrusion machine. Nylon is heated and squeezed through a small hole (extruded) to make mono-filament nylon line. All plastics naturally shrink during processing and if the extrusion process isn’t very carefully controlled the string diameter and even density can vary. Rectified plains start off as extruded mono-filament, like the ordinary plains, but of a slightly larger diameter. Then they pass through a further precision grinding process to make them as round and as uniform in diameter as possible, which ensures the most accurate intonation at any fret. The grinding process leaves these rectified strings looking opaque with a matt textured surface.

The black and other coloured plain strings are simply dyed nylon. Some people confuse these with the so called ‘carbon’ strings, assuming that carbon means carbon fibre and that since carbon fibre is black then the black strings must be carbon fibre or even that any strings referred to as ‘carbon’ are carbon fibre..
Carbon fibre is a term used to describe a rigid moulded composite fibre and resin material that resembles fibre glass except the fibres used are made by heating or carbonising an extruded plastic mono-filament pre-cursor, usually PAN or polyacrylonitrile. While this is a splendid material for building guitar bodies and necks it has nothing to do with strings and so called ‘carbon’ strings are probably made from a fluorocarbon based plastic, rather than nylon. This makes for a tougher, denser, thinner string than nylon, that the manufacturers claim has better tone.
Similarly Galli’s new Titanio treble strings are described as being made from ‘titanium’ nylon. This is just their way of describing an improved formulation of nylon. The strings are not made from, or contain, the metal titanium.

Wound ‘nylon’ strings are also available with some variations, such as a bronze wrap wire for a brighter tone than the traditional silver plated copper wound string. Some wound ‘classical’ strings use advanced plastics for the fine multi-filament core. The French maker, Savarez, makes wound strings wrapped with polished pure silver wire for ‘squeak free’ playing and even makes plastic wound plain strings for their different tone.

The floss polymer used in wound cores is almost always nylon, and the monofilament polymer is usually nylon, but it sometimes is polyester, kevlar or polyvinylidene fluoride (PVF)

In conclusion

The relatively simple construction of musical instrument strings means that the opportunity for progress is held to fairly narrow bounds and the limitations of current strings still place limits on instrument design, just as they have in the past. For example the limits of available strings make it quite difficult to extend the pitch range on one guitar as demonstrated by the design problems faced by Roger Bucknell in creating the amazing 8 string Fylde custom guitar featured in a previous issue.

Although there is only a relatively small amount of material in each set of strings, worldwide many thousands of old strings are thrown away every day. Shortages of the raw materials, like copper, could affect the price and availability of strings. Who knows, perhaps one day string recycling banks will start to appear in music stores.

By – Terry Relph-Knight