The acoustic guitar strings

How are they made? How many types exist? Which one to choose?

Here we need some patience, as the strings topic is particularly complex and tricky, for many reasons. On the one hand, we must consider construction techniques, different materials employed, usable gauges. On the other hand, to choose the correct strings we must analyse subjective and objective factors like playing skills (sensitivity, strength, technique), musical genre, the features of the instrument used (the scale length, for instance) and of course the personal tastes of the musician. But one thing you can take for sure: strings are an essential component if not crucial for the “sound” of any musician.




Typology and construction


The strings for acoustic instruments are called steel strings (made of steel), to distinguish them from those used per the classic guitar (nylon strings). They are further divided into two types: wound and plain strings. The wound strings (D, A, E low) have metal windings around their core, that can have different shapes (round, but more often hexagonal to maximize the stability of the windings). The windings of the strings for electric instruments can be made of different metals: bronze, bronzed steel, phosphor bronze, silver, nickel.
The core/winding combinations create many different kind of strings. Some of the most common are:




• Bronze 80/20: steel core + bronze wound
• Phosphor Bronze: steel core + phosphor bronze wound (the phosphor treatment increases the life of the string)
• Bronzed or Steel: steel core + bronzed still wound
• Brass-Plated Steel: bronzed steel only, without winding
• Silver-plated Wound: steel core + silver wound
• Silk & Steel: silk core / steel wound + bronzed steel or bronze
• Nickel Wound: nickel wound
• Pure Nickel Wound: 100% pure nickel
• Flat Wound: steel core + flat steel wound
• Round-wound: the winding wire has a round cross-section. The sound is usually bright, powerful, good for every musical style.

The different type of windings influence the longevity of the string, the tone, the fret wear, and of course the final cost. For instance, the Nickel-wound strings offer low fret wear and are cheaper than the Bronze-wound, while the Silk&Steel feel softer and warmer thanks to the insertion of silk-like materials in the winding process.

There are some special treatments that can increase the useful life of the strings:
Cryogenic: using the possibilities of changing the alignment of the granular structure of metals (at about -190°) the strings become more resistant to oxidation and preserve their tone for a longer time.

Coated: ideal for the guitarists allergic to nickel, this further coating (polymeric based) extends the useful life of the strings. This coating wears off with intense and prolonged bendings and playing with a very aggressive strumming.

The different types of windings

From the construction point of view, there are 3 main types:

• Flat-wound: the winding wire has a rounded square cross-section. They feel smooth under the fingers, so is their sound, rounded on the low notes. They also produce less “sliding noise” from the fingers moving on the strings. Mainly used in styles requiring clean sounds, like jazz.
• Half-round wound: the winding wire has a variable degree of roundness of the square cross-section. It is a sort of cross between round and flat wound, with a muffled “sliding noise” and a brighter tone, qualities that can vary depending on different roundness of the winding wire.

The core
The core is the plain piece of steel that corresponds to the string itself in the case of plain strings, and has a round cross-section, while for wound strings the cross-section can have mainly two shapes: rounded or hexagonal.

Round core: with this solution the windings have a 100% contact with the core, the string can vibrate more freely with a louder volume and a slower attack than a hex core string. Nevertheless, the round shape causes an inferior stability of windings, that sometime results in difficulties of intonation of the string. Moreover, as the string vibrates in every direction and more freely, an higher action must be set than a hex core string, to avoid noises from the string touching the frets. For these reasons, together with higher manufacturing costs, many manufacturers offer more and more hex core strings.

Hex core: the hexagonal shape of the core offers more stability of windings, resulting in higher precision and better intonation of the string. The string can vibrate less freely, with a softer volume and a faster attack that allows for a lower action adjustment than a round core string. Finally, the hex core string offers lower manufacturing costs than a round core string.

Core to wrap ratio
When buying strings of a different brand or different series from the same brand, sometimes you note that some strings (of the same gauge) are sonically different, and need different tension. Why? It is not a manufacturing fault, but an effect of the design and manufacturing of the string. As a matter of fact, also the core to wrap ratio has an effect on the physical and tonal characteristic of the string: a string whose winding wire diameter is larger than the core diameter will sound brighter and feel more flexible. On the contrary, if the core diameter is larger than the winding wire diameter, the string will show more sustain, volume, longevity and tension.

The gauges
The tension created by a string set depends on the gauge of each string in the set. Thinner string gauge corresponds to less tension and consequently both the string action and the truss rod adjustment for a correct neck setup must be calibrated.
Generally speaking, acoustic guitar strings are heavier than those used for the electric guitar, and most common string sets commercially available are:

• Extra light (.10/.47)
• Light (.11/.53)
• Medium (.12/.53)
• Medium for 12 strings guitar (.10/.47 - .10/.27)
• Heavy (.13/.56 - .14/.58)
• Heavy for 12 strings guitar (.11/.50 - .11/.28)

Buying single strings, we can create personalized sets to meet our particular needs. On the acoustic guitar often non-standard or open tunings are used, based on unusual intervals that can require different gauges to handle the tensions that differ from the standard tuning. Some example: a Plain Steel can range from .07 to .24, a Bronze 80/20 from .20 to .59, a Phosphor Bronze from .20 to .70.