Adding Warmth to Your Tone By Changing Strings

Acoustic guitar strings that emphasize bass and mid-range frequencies, along with second-order harmonics are best for achieving a warm sound. Medium gauge, phosphor bronze, flat wound, and round core strings will accentuate the bass and mid-range frequencies most effectively.

Acoustic guitar strings that best exhibit these qualities include:

• Thomastik-Infeld Spectrum Bronze Acoustic Guitar Strings
• John Pearse Phosphor Bronze Acoustic Guitar Strings
• Martin & Co. Authentic Acoustic SP (Phosphor Bronze)
• Martin & Co. Retro Monel Acoustic Guitar Strings
• Earthwood 80/20 Bronze Acoustic Guitar Strings
• D’Addario Phosphor Bronze

While tone is subjective when it comes to the acoustic guitar, guitars described as having a warm tone tend to be held in pretty high regard. But what really is a warm tone and is it possible to warm up the tone of your existing guitar?

There’s a lot you can do, from changing picks to adjusting the picking hand position, but perhaps the simplest thing you can do is experiment with a new set of acoustic guitar strings.

In today’s article, we’re going to take a closer look at acoustic guitar strings, and how they contribute to tone taking into account string gauge, winding materials, winding type, core shape, and coatings.

So, while this article focuses on tone, it’s also a fairly detailed guide to acoustic steel guitar strings in general so if you are interested in learning more about either stay tuned!

What is a warm tone?

Before we discuss your choice of strings we need to define what warm means in the context of guitar tone as most of us probably know it when we hear it but like describing the concept of color to someone who can’t see, it’s difficult to define.

Many consider analog (e.g. vinyl LPs) as warmer sounding than digital (CD and DVD), and in a sense, this is a good starting point (more on this shortly). But, often, this type of debate tends to get bogged down quickly with useless terminology to describe tone such as ‘character’ which just isn’t all that helpful to someone wanting to understand tone.

So rather than get bogged down using similar terms to describe a warm tone, let’s take a more scientific approach.

You probably are already aware that there’s a huge amount of terminology used to describe tone. I’ve listed some of the more common ones here but if we had to break it down to just three, the most commonly used are:

What are low, mid-range, and high-range frequencies?

If you don’t know much about frequency with respect to pitch, I’ve written a bunch of information here, but in simple terms, sound is created when something vibrates. The faster the vibration the higher the pitch.

This is easy to observe by playing an open string and then fretting the string higher up the neck. By shortening the string we reduce the length, and mass of the string causing the string to vibrate faster. This results in a higher pitch being produced.

The number of vibrations is measured in terms of complete vibrations of the surrounding air particles per second, expressed as Hz (hertz), or kHz (kilohertz). Humans can generally hear frequencies between 20 and 20,000 Hz (20 kHz).

There are 7 standard frequency bands (as listed below).

Just to provide a quick example the table indicates bass frequencies to be between 60 and 250 Hz. This frequency range is considered ‘warm’ which essentially means the mid to upper bass frequencies are accentuated without a noticeable loss in clarity. As we can see, in the next highest frequency band, emphasizing frequencies in the low mid-range will begin to sound muddy e.g. lose clarity.

Remember when we discussed vinyl earlier?
One limitation of vinyl is the fact that bass takes up more space than treble. To compensate for this some audio engineers would emphasize the low mid-range e.g. between 100 and 250Hz which is the range usually associated with a warm tone, as above in our table.

Second-order harmonics

When you hit a note on your guitar the string vibrates and the most prominent sound you hear is referred to as the fundamental tone.

However, the string vibrates in different ways resulting in additional frequencies also being heard, these are referred to as overtones and add complexity to the sound, which you may hear referred to as ‘richness’ in common tone terminology.

This series of overtones and how they are emphasized and decay is what gives instruments their unique sound, referred to as timbre. This is why a guitar sounds different from other instruments despite playing the same note.

Harmonics are simply overtones that are multiples of the fundamental tone. In this sense, second-order harmonics are overtones that are double the fundamental frequency (e.g. they vibrate at twice the frequency of the fundamental and are also known as ‘even harmonics’ due to being an even multiple of the fundamental tone).

Second-order harmonics are often referred to as thick and warm sounding and are thought to decay less rapidly than higher-order harmonics. If interested in learning more, the video below is worth checking out.

Describing tone

Tone is more nuanced than the explanations above, however, and the terminology used can be hard to define because like tone, the terms we use to describe tone are also highly subjective (e.g. one guitarist’s warm tone is another’s ‘muddy’), and contextual.

In any case, guitars aren’t strictly warm, balanced, or bright. They are combinations of all three and more. In this sense, a definition of ‘warm tone’ might be something like the following:

A warm guitar tone emphasizes bass and mid-range frequencies in the 60 – 250hz range and accentuates second-order harmonics without sacrificing clarity and becoming muddy sounding.

OK, enough about the specifics of a warm guitar tone. Based on the above, we now know our strings need to emphasize the bass (60Hz) to lower mid-range (250Hz) frequencies without sacrificing clarity while accentuating second-order harmonics.

Why do your acoustic guitar strings contribute to tone

People often say it is better to have a bad guitar with good strings than a good guitar with bad strings. This is true but could be taken a step further to say it is better to have a bad guitar with the ‘right’ strings.

As an example of this, when I first got into guitar, one of my absolute favorite guitarists was Stevie Ray Vaughan (#RIPSRV). My brother and I would sit around our family stereo in the living room for hours listening to the posthumous ‘The Sky Is Crying’ over and over, particularly ‘Life By The Drop’ one of the few acoustic guitar songs SRV recorded.

Later on, upon hearing SRV’s unplugged session for MTV I began to appreciate his approach to the acoustic, he attacked it like he did his electric guitar, and that stuck with me, as someone who loved bands that featured electric guitar but preferred playing the acoustic guitar.

In any case, I was young and a little naive, because when I realized that SRV played with heavy gauge GHS strings I did the same and stuck solid, on both electric and acoustic, even though this was probably just referring to his electric guitar (number one) and not the 12 string Guild I’d seen him play.

I did this for many years, and while I changed guitars I kept playing those thick GHS strings, after all, who had better tone than SRV? No-one.

The thing was, while the GHS strings did sound great to my albeit untrained ears when I eventually tried a set of medium gauge Elixirs on that same beat-up old dreadnought I realized they made the guitar sound a lot more resonant and seemed to add a lot of complexity to the tone (e.g. brought out more of the overtones, as described above).

I’d imagine it was something like the difference between going from a cheap red to an expensive red wine with a more sophisticated palette, suddenly there was just a lot more going on.

Being the slow learner that I am I naturally assumed Elixirs were just better-sounding strings. But, when I put a set on my next acoustic guitar (a smaller body Guild) I didn’t like the tone nearly as much it sounded choked, and lacked sustain compared to the original strings.

After playing around with a few different sets of strings I finally settled on D’Addario Phosphor Bronze which again seemed to bring this smaller-bodied guitar to life.

What does all this mean? I’ll let Tommy Emmanuel, one of the very best acoustic guitarists ever, explain:

Guitar string specs to consider with regard to warmth

So what specifications are most important concerning tone on a typical acoustic guitar string? All of them, including:

• String gauge
• Winding materials
• Core shape
• Winding type
• Coatings

Guitar string gauges for a warm tone

String gauge refers to the thickness or diameter of the string, measured in thousands of an inch. String thickness includes the core wire along with the thickness of the winding wire, times two, to account for wrapping around the central core wire.

Generally speaking the heavier the gauge of the string the more emphasis is placed on the mid to low-range frequencies. The lighter the string the higher frequencies are emphasized, and the brighter the tone, all things being equal.

Guitar strings – light vs medium

The most common acoustic guitar string gauges are light and medium, and to a lesser extent heavy. Extra light (aka super light) and super extra light are less common but you generally won’t have any trouble picking up a set from your local music store all the same.

A set of extra light gauge strings for acoustic guitar ranges from .010“ on the high E to 0.47“ on the low E while a set of heavy gauge strings will typically range from .014” to .59”. Most acoustic guitarists use extra light, light, or medium gauge with far fewer using heavy gauge strings.

Electric guitar strings are lighter than acoustic guitar strings in general e.g. light gauge on an electric guitar is lighter than the light gauge on an acoustic guitar. The reason for this is explained in detail here.

But for the most part, ignore where it says light, medium, or heavy on the packaging and instead refer to string gauge. Light and heavy are not a strict set of standards, so there may be differences between brands. It’s also true that the markers appear to be shifting e.g. what was once considered light when I was first learning guitar, in some cases is now referred to as medium.

When referring to strings by gauge we tend to name them by their high E strings, so a set of .010” to 0.47” is referred to as 10’s, and a set of .014” to 0.59” is referred to as 14’s.

What are light/medium string sets?
There are also ‘hybrid’ sets available which utilize lighter gauge strings on the first three strings and medium gauge on the three bass strings. They are designed to offer the best of both worlds, so to speak, with accentuated bass response, along with lighter treble strings that require less effort to fret.

How string gauge affects tone and playability

When it comes to string gauge there’s more to consider than purely tone. Different string gauges exert different amounts of tension on the guitar neck, which has an obvious effect on playability and indirectly affects tone.

For example, a heavier gauge string will generally emphasize the lower frequencies along with greater volume and sustain. But, the lighter the gauge of a string the more easily the guitarist can fret and bend notes.

The heavier the string, the more tension, with the string being more difficult to fret. But, if you are predominantly a slide guitarist or mostly strum chords this additional tension will be far less of a concern from the perspective of playability, and not worth compromising the additional warmth, volume, and sustain.

So, while one gauge of string might be considered ’warmer’ and fuller, it also comes down to the guitar, the style of music or technique e.g. fingerstyle or strumming, and the guitarist themselves as to how they utilize the string gauge being played with e.g. they may use a thicker gauge pick, which also affects tone because they play a heavier gauge of string.

Speaking of heavy gauge strings. Remember when I mentioned SRV earlier?

He used a .013“ high E string, a very thick gauge for the electric guitar. For comparison, most guitarists of that era were using 9’s (Billy Gibbons even used 7’s) hence the gauge and not just the brand were probably one of the biggest factors in the great man’s tone.

But not many people could have played the way he did with that much string tension. Fortunately, by all accounts SRV was a considerate guy, otherwise, he may have crushed a few hands greeting fans.

Problems associated with using heavier gauge strings

While it’s a good idea to experiment with different gauges in pursuit of tone also keep in mind any major departure from the gauge you usually use or that your guitar has been set up for will alter the amount of tension on the neck.

Increased or reduced tension can reduce or increase the relief of the neck e.g. the outward or inward bow of the neck, which in turn affects the height of your strings in relation to the fretboard (action). It can also exert additional tension on the bridge, which in some extreme cases requires the bridge to be repaired due to lifting away from the soundboard due to the increased tension.

In the case of going from light to heavy strings, or vice versa a truss rod adjustment may be required but it is best to let the guitar settle for a few hours after installing new strings before doing so.

Which gauge string is best for a warm tone?

The heavier the gauge the more contribution to a warm tone, but, the more effort required to play which indirectly affects tone. E.g. there’s no point in having strings that sound great if they hinder your playing.

Another option is to try hybrid strings which combine the warmth of heavier gauge bass strings with the lower tension of lighter gauge treble strings.

Core shape

If you look at a cross-section of a wound string (acoustic guitars usually have four wound and two unwound strings) you will see the outer windings are wrapped around a hexagonal steel core.

While hexagonal cores are more common nowadays at one point round-core strings were the only available option.

Hexagonal core wires were developed mostly for greater efficiency in manufacturing, as they allowed machine winding to be more reliable. Round core wires were also more susceptible to unravelling as the round core surface didn’t provide as much grip as the harder edges of the hexagonal shape.

But, while debatable, many claim round core wires offer advantages over hexagonal cores (more flexible, longer-lasting, better clarity, more sustain, and a warmer tone) for the guitarist.

Because of this, and as a result of manufacturing technologies becoming more sophisticated over time, more round-core guitar strings are being developed again.

Does core shape contribute to a warm tone?

It’s not so much that round core wires have a natural tendency to sound warmer, it’s more the case that hexagonal cores are said to increase brightness. This is due to the lower density of the string.

For example, the entire surface of a round core wire is in direct contact with the winding material. However, a hexagonal core is only in contact with the windings on the edges of the hexagon shape. This creates small pockets between the windings and the core along the surfaces of the core wire, reducing the density of the string and accentuating brightness.

Winding materials

The majority of acoustic guitar strings consist of a core of steel, the same as electric guitar strings. The main difference between the two with regard to materials is the materials used for the windings on the G, D, A, and E strings.

Due to relying on electromagnetism to generate sound, electric guitars require strings to have windings with magnetic properties, e.g. steel, nickel, or chromium.

Alternatively, acoustic guitars can use different materials, and different combinations of materials, chosen mostly for their resonant or tonal properties. The two most common options are 80/20 Bronze and Phosphor Bronze, along with the addition of less common materials including silk.

80/20 bronze

80/20 Bronze strings are a combination of 80% copper and 20% zinc, which results in brass and not bronze.

However, much like a tremolo bar is used on the electric guitar to impart vibrato, rather than tremolo specifically, these names tend to stick when it comes to guitars and therefore 80/20 bronze strings, despite being brass, are thus named 80/20 bronze.

They are credited for their crisp, bright tone. However, on average they tend to have a shorter lifespan than phosphor bronze strings and therefore do not retain that brightness for long, depending on how often the guitar is played. And, while some guitarists prefer the sound of slightly worn 80/20 bronze strings, they tend to require replacing more often if you want to retain that new string sound.

Phosphor bronze

Phosphor Bronze strings are bronze wound strings with phosphor added to make them more resistant to corrosion. Because of this, they tend to retain their tonal qualities and elasticity for longer than 80/20 bronze string. They are also typically credited with a more balanced, warmer tone.

Silk and steel

While silk and steel strings still go by this name, they mostly no longer use silk and instead consist of nylon. The nylon filament serves as a sleeve, sitting between the steel core and the metal windings on the wound strings. Due to this ‘protective layer’ serving as a barrier between the two materials the strings themselves project less volume but alternatively are softer on the fingers making them a good option for fingerstyle guitarists. They can also be tuned to pitch with less tension. While not usually described as a ‘warm’ sounding string, they are often described as mellower sounding and tend to feel more like classical guitar strings.

Monel

Monel is an alloy made up of approx. ⅔ Nickel, ⅓ Copper with small amounts of Iron also present. It was chosen as a material for steel guitar strings as it offers resistance to corrosion, along with great clarity, especially in the lower frequency ranges. This material was one of the first materials used for steel-string manufacturing but due to high production costs were phased out for many years, however Pyramid, Rotosound, and others now include string sets that utilize Monel.

Winding type?

Winding type refers to the profile of the wires used on the wound strings. They come in three options:

Roundwound

Roundwound strings have, as the name implies, a round profile as shown in the example above.

They are less expensive to manufacture and as a result, are also more affordable than flatwound strings. Because of this, they tend to be more common i.e. most strings are round wound. But, they also tend to wear out faster than flatwound strings.

Due to the round profile (which separates more easily when bending a string for example), they are also more flexible. And, due to the round profile offering a gap between the individual wires offers a more textured feel against the fingers, which also results in more string noise when compared to flat-wound strings.

They are also credited with a brighter sound than flat-wound strings and offer greater volume and sustain.

Flatwound

Flat wound strings offer a flatter, smoother surface due to the square profile of the surrounding wires. They cost a little more to make and as a result, cost more to buy, however, they are known to last significantly longer than round wound strings.

The flat surface allows the fingers to glide over the strings with less friction, reducing string noise between the strings and the fingers. However, they also require more effort to perform bends as the profile of the surrounding wires does not separate in the same way as round wound strings.

They tend to offer a warmer sound, with more of a focus on the fundamental tone and less on harmonics.

Halfwound

Halfwound is a compromise between both methods, with the individual wires made partially square. They are far less common, however.

Which contributes most to a warm tone?

There is no question that flat-wound strings offer a warmer tone than roundwound strings, all things being equal. This is why they are associated with the jazz guitar community as jazz guitarists tend to favour warmth over brightness, generally don’t perform a lot of bends, and favour clarity over sustain.

The real question is how much they contribute. And are the tonal benefits a fair compromise between the lack of string flexibility and additional cost?

Coated strings?

Lastly, we’ll take a quick look at coated strings. Coated strings come with a polymer coating of plastic and resin. Elixir strings are a brand well-known for their coated strings, however, most major string manufacturers now offer a coated string.

The coating serves as a barrier between the strings that are normally subject to corrosion from sweat, and added mass from dead skin cells and grime. The coating prevents the strings from being clogged up and enables them to last longer and retain their tonal qualities.

However, some claim that coated strings are less articulate, to begin with. I think it depends on the application. I prefer coated strings on a ‘strummer’ e.g. a dreadnought or larger-bodied guitar, but prefer uncoated if playing with just the fingers.

Generally, coated strings are more expensive, with some being twice the cost of uncoated strings. However, thanks to the coating, the strings tend to last considerably longer.

Are they worth it? It depends, are you fastidious about washing your hands before playing? Do your hands sweat a lot when you’re playing? If so, coated strings are probably worth a shot. While costing more upfront, if you run through strings fairly quickly you will probably save money over the long term.

Do Coated Strings Affect Warmth?

Much like string core shape, it’s not so much that the coating contributes warmth to your overall sound. It is more the case that coated strings reduce brightness which is the most common complaint in terms of coated strings, they lack brightness.

As we discussed in the first section on tone, warmth is not the polar opposite of bright, so an absence of brightness doesn’t necessarily mean the strings offer a warm tone, but Elixir Polywebs (a coated string from Elixir credited with a warm tone) have a thicker coating than the other two coated string offerings from Elixir (Nanoweb and Optiweb).

Strings and tone

Changing your strings?

Nick Drake is renowned for his acoustic guitar tone. The video here is a great breakdown of his tone and includes ideas on how to replicate it. One of the ideas mentioned is using older strings.

Do old strings help create a warm tone? If you consider new strings are known for their brightness, then it makes sense to assume older strings sound warmer. This is why some jazz players don’t change strings as regularly as guitarists in other genres.

Guitar strings wear out over time mostly due to a loss of elasticity and additional mass added to the strings over time.

One way to keep that old string feeling but reduce the accrued grime and salt from deposited sweat that would otherwise cause corrosion is to boil your strings. Although this is more common among bass players, due to the cost of bass strings compared to guitar strings it’s worth trying if you prefer the sound, and feel of old strings.

What about nylon strings?
Being a fan of both steel string and nylon string guitars, I’d normally cover both here. But in the words of the great late, great Andrés Segovia, the guitar (he was referring to classical guitar) is like a mini-orchestra, meaning a lot of different tones are extracted from a nylon string guitar, and much of this comes down to playing with the nails, and the shape of the nails.  However, I will be writing another article on classical guitar strings shortly so stay tuned.

Final thoughts

Now that we have established what a warm tone is and how the different aspects of string manufacturing (string gauge, winding materials, winding type, core shape, and coated strings) affect tone, what recommendations are we left with?

While many different aspects of the guitar itself can affect tone e.g. body shape, tonewoods, and the age of your strings, a good starting point would be to try a flatwound, medium to heavy gauge, or bronze phosphor string. But also experiment with coated strings and round core wires, along with numerous other combinations of materials before settling on the right strings for your guitar, your style of playing, and most importantly your musical tastes.

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