Most guitar string sets today consist of a mix of plain steel strings and wound strings. Plain steel strings are typically used for the thinner gauged strings in our sets and are simply one piece of cylindrical steel wire running the entire length of the string. 

However, things get a little bit more interesting when we start to look at our wound strings. For electric string sets, the wound strings are usually our fourth, fifth and sixth strings and for acoustic sets you usually come across a wound third string too.  Bass sets nearly always consist of wound strings.  No matter what instrument you play, these wound strings are made up of two constituent parts: a central core wire and an outer wrap which travels around the core. 

In today’s blog, we’re taking a closer look at the shape of this central steel core.  Why’s that? Well that core comes in two main shapes: hexagonal shaped and round shaped (or more commonly referred to as hex core and round core). But what’s the difference? And how do they compare to one another in terms of sound and feel? We’ll try and tackle all these pressing questions below to help improve your ‘core knowledge!’

Round Core Strings

We should start by saying that round core strings (sometimes referred to as vintage core) were very much the norm back in the days way before hex core strings were even invented.   In fact, piano strings and other classical instruments have been using round core strings for centuries.  

If we were to slice through a round core string, you’d see that the core is (as the name suggests) round shaped. Because of its smooth outer edge, as the outer wrap wire travels around the core it remains in complete contact with the core’s entire outer surface.

Above: The outer wrap wire remains in contact with the entire surface of a round core string.

Nowadays, whilst most manufacturers lean towards producing hex core strings (more on that below) round core sets are still available with brands such as Thomastik, Pyramid, Martin and DR still very much flying the flag. In fact Michigan based string manufacturer GHS’ flagship electric string line (GHS Boomers) are primarily wound on round cores which in the modern era of string building is quite unusual.

Hex Core Strings

As you will have probably guessed, instead of being circular, the central core of a hex core string is shaped like a hexagon with 6 sides and 6 corners. Because of its shape, the outer wrap wire doesn’t make complete contact with the core’s entire surface, instead during the manufacturing process, the wrap wire digs into these six corners. 

Above: As you can see the wrap wire only makes contact with the hex core's six corners rather than being in complete contact with its entire outer surface.

Hex core strings are more or less the norm nowadays when it comes to the manufacturing of guitar strings. This was a production technique first adopted by D'Addario back in the 1930's but most of the popular brands you see on our website including Ernie Ball, Elixir, Rotosound and more all favour a steel hex core for all of their strings whether they be for electric guitar, acoustic guitar or bass guitar.

So what’s better, Hex Core or Round Core strings?

If you’re partial to scouring the guitar forums online, you may have come across threads dedicated to this very topic.  Of course, certain players certainly have their preferences and strongly voice their opinions on what’s best but there’s definitely no ‘correct’ answer to this question.  All we can say is that both have their own unique characteristics which are certainly worth considering to see which sets might suit your guitar and style of playing.  Here’s a few things we think are worth pondering;

Tonality

The way in which hex core and round core strings are constructed, certainly influences the final tone they deliver.

For round core strings, because the central core is in complete contact with the outer wire for the entire length of the string, as the string is struck the core and wrap wire move as one nice compact unit delivering a lovely deep, boomy tone.

GHS (a big round core advocate brand) actually state on their website that round core strings use larger core wires when compared to hex core strings.  This gives the string more mass, resulting in more output which is another reason why they deliver the tonal characteristics they do.

In stark comparison, hex core strings deliver a brighter tone with a more pronounced attack. 

In fact, despite GHS Boomers utilitising round cores for the majority of the gauges in their range, they say they use hex core strings for their thicker gauges (.060 and above).  They cite the reason for this being that “as string gauges get thicker, the added stability that the hex core provides makes it ideal to retain clarity and definition on lower strings, specifically the B and F# strings found in our 7 String Boomers and 8 String Boomers”

You could say that round core and hex core strings represent vintage tone (round core) vs modern tone (hex core).  In fact, sometimes round core strings are referred to as vintage core strings.  For example, Fender fairly recently released their Classic Core strings that utilise a round core and they use the term vintage core on their packaging.

Whilst many string brands made the move over to manufacturing their products using hex cores as a way of improving efficiency, the added brightness and clarity that hex core delivers also handily plays into the tonal demands of the more modern player.

In more recent years, there has been a growing throng of players using drop tunings coupled with high gain rigs.  Pairing these two things together can often lead to an undesirable ‘muddy’ sound so using a hex core set would certainly help to retain some clarity and punch, helping to stand out and cut through the mix.

On the other hand, players who are fans of vintage tones and gear might look to explore the sonic possibilities that a round core string can deliver.

Because round core strings have a slightly mellower tone to begin with you may not necessarily notice such a ‘drop off’ in brightness over their lifespan in comparison to a hex core string which starts off with noticeably more sparkle. 

Chas Johnson added a really valid point which also helps to explain why hex core strings tonality may tail off seemingly quicker than round cores;

“sweat and body oils from the skin and string cleaners (like Fast Fret) permeate between the coils of the outer wrap of the wound string and accumulate in the voids around the hexagonal core. Crud builds up inside the string, which can’t then be cleaned and the string goes dull more quickly than with a round core string, which doesn’t have those voids for muck to build up inside.”

Flexibility

The level of contact between the core wire and wrap wire of round core and hex core strings is pivotal in how each type of string feels and plays.

We often liken the two parts of a round core string to two professional salsa dancers… both in sync with each other, the core and outer wire move with a lot of fluidity and flexibility.

On the other hand, because the core of a hex core string digs into the outer wrap wire, it creates a “tighter” bond which also makes the string feel slightly stiffer under the fingers.

Chas added to this;

“For the same wound string gauge, a string with a round core would be expected to have lower tension than a hex core string. This makes it slightly easier to bend and also means that you can go up to a slightly thicker string gauge in round core and have the same feel as a thinner hex core string (this applies to the wound strings only). This then means that you have more mass moving in the magnetic field over the pickups which helps to generate a higher electrical output from the pickup. It can also be a benefit on fragile old acoustic guitars that need light tension strings as it can give you a bit more mass to help produce a better bottom end tone than you might get with very light hex core strings.”

Tuning

As we all know, staying in tune is imperative when it comes to playing the guitar. For this reason, tuning stability is possibly the biggest talking point when it comes to the differences between round core and hex core strings.

This all boils down to how the inner core and wrap wire are connected.  As explained earlier, hex core strings ‘grip’ hold of the outer wrap wire much tighter than a round core string does and it’s this bond that really helps to maintain tuning stability. 

Because round core strings don’t have such a tight grip, in some circumstances the tension holding the core and the wrap wire can get lost and these two parts become slightly detached from one another.   Tonally, this results in the string sounding ‘dead’ which is unfortunately irreversible and therefore a new string will certainly be needed.  This can often happen when the strings are trimmed prior to them being fitted to an instrument (more on this below).

We mentioned earlier that many string makers have made the switch to using hex core strings and Chas pointed out that “this shift was nothing to do with tonality differences.  It was all about making strings cheaper to manufacture and reduced the likelihood of a dud string getting through quality control.”

So generally speaking hex core strings do hold their tuning more consistently than round core strings.  But, does this mean that round core strings inherently have tuning issues? Certainly not, and if this is how they are sometimes perceived, they are arguably misunderstood.  There’s nothing to fear with round core strings, all that’s needed is just a little care and attention when fitting these to your instrument;

Don’t trim too early!

As mentioned above, we need to avoid losing that tension between the core and the wrap wire which results in a dead string.

Before we explain the very simple process, it helps to understand how this tension is maintained in the first place. When a round core string is made, the outer winding is flattened off at the tail end of the string where the winding finishes. It’s this flattened area that allows the outer wrap wire to remain attached to the core from the factory. This is a technique taken from piano string production and this flattened area is known as a “swedge.”

When you trim a round core string this all important swedge is removed, meaning there is an increased likelihood that the core and wire become detached from one another. 

At this point, if you own a guitar with vintage style tuners, you’d be forgiven for wondering if you can even use round core strings as the strings need trimming prior to being fitted to the tuner?  If there’s a risk of the string being dead before we even fit it, surely they are a no go?  Fear not, all we need to do is to replicate the ‘swedge’ somehow to help maintain the tension.  Here’s how;

STEP 1) Start by locating the point where you would normally trim the string. 

STEP 2) At this point, instead of cutting the string, make a nice tight 90 degree bend in the string.  

STEP 3) About 2cm beyond this bend you can then trim the string.   This bend will act as our mock ‘swedge’ helping to maintain the tension between the core and outer wire and the crimped and cut end of the string now resists any temptation for the windings to slip on the core.

So, just remember it’s a case of ‘bend then trim’ not ‘trim then bend’ when it comes to round core strings.

If you’re not sure whether a set of strings has a hex core or a round core, be sure to check out the listing on our website as we specify this attribute on each of our sets.  Round core strings are available in electric, acoustic and bass sets.

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As you can see there’s a little bit more to cores than initially meets the eye. Both types of strings certainly have their advantages and individual quirks and you may find that one particular type lends itself more to your style of playing. Although there is a far greater choice of gauge and wrap material on the market when it comes to hex core strings, round core strings certainly offer something different in terms of feel and tone so it’s certainly something worth exploring further.

Be sure to check in with us in the future where we’ll be talking more about cores and in particular the ratio in size between the central core and the outer wrap wire.

Feel free to pop in your comments, questions and share your experiences below as we love hearing from you.

**As always, tip of the hat to our man Chas J for his eternal wisdom and input