Martin MA540FX Flexible Core Phosphor Bronze (.012–.054): Tommy Emmanuel's bend-easy set
Reviewed by the Change Your Strings editorial team ·
Martin MA540FX Authentic Acoustic Flexible Core is a 92/8 phosphor bronze acoustic string, .012 to .054 Light, built with a thinner core wire under a heavier wrap for easier bending and less finger fatigue. Martin originally engineered it for beginners, then fingerstyle virtuoso Tommy Emmanuel adopted it as his touring set, branded 'Tommy's Choice.' Same alloy and gauge as Martin's standard MA540, just softer under the fingers.
What this set is
Martin MA540FX is the company's Flexible Core phosphor bronze acoustic string in Light .012 to .054, the same gauge and 92/8 phosphor bronze family as Martin's standard MA540, built around a thinner Superior Performance (SP) core wire under a heavier wrap. Martin's own product page describes the construction plainly: designed to reduce finger fatigue and allow huge bends.
On Martin's own site, this exact Light gauge variant is labeled "Light, Tommy's Choice" in the product's gauge selector. That's not a marketing nickname CYS invented. Fingerstyle guitarist Tommy Emmanuel is the namesake, and the story behind the name is more interesting than a typical signature-string deal: Martin built Flexible Core for beginners first, and Emmanuel adopted it for the opposite kind of player years later.
Anatomy
- Model
- Martin MA540FX Authentic Acoustic Flexible Core (Tommy's Choice)
- Gauge
- .012 – .054 (Light)
- Gauge set
- .012, .016, .025, .032, .042, .054
- String count
- 6 strings
- Core wire
- SP (Superior Performance) high-tensile steel, thinner 'Flexible Core' gauge under a heavier wrap
- Wrap wire
- 92/8 phosphor bronze (92% copper, 8% zinc)
- Coating
- None, uncoated
- Winding
- Standard roundwound
- String tension
- 168.7 lbs total, per Martin's own gauge and tension chart
- Intended scale
- Fits Martin dreadnoughts and most production dreadnought, OM, and parlor acoustic guitars
- Intended tunings
- E standard primary; handles Drop D without re-gauging
- Made in
- United States, Martin's own factory (Martin has manufactured its own strings since 1970)
- Pack sizes
- Single (Light, Tommy's Choice) or 3-pack, per Martin's own product page
MA540FX Authentic Acoustic Flexible Core (.012–.054)
Why Flexible Core bends easier
Every acoustic string has two parts on the wound strings: a core wire and a wrap wire coiled around it. Martin's regular SP core wire is built at one thickness across its standard Authentic Acoustic line. For Flexible Core, Martin slims that core wire down and thickens the wrap wire to match, so the finished string still measures the same gauge Martin prints on the pack. What changes is how the string feels under your fingers: a thinner core flexes more easily than a thicker one, so bending a note or fretting hard takes less effort, per Martin's own description of the construction.
Emmanuel on why he sticks with Martin's Flexible Core construction night after night on tour.
I can put on a brand new pair of strings and not check my tuning for five songs, and it'll still be perfect.
Fingerstyle guitarist, Grammy winner, Certified Guitar Player
Martin didn't build this construction for virtuosos. Per Martin's own account, Flexible Core was originally aimed at beginners, whose fingertips haven't callused yet and whose technique benefits from a string that gives a little. Emmanuel came to it from the opposite direction: Martin gave him early Flexible Core prototypes to test on a Canadian tour around 2009 or 2010, the third string kept breaking, Martin reworked the construction, and the result became his regular touring string, the one Martin's own blog says he puts on fresh before every show. The two audiences want the same thing for different reasons: a beginner wants a string that doesn't fight sore fingers, and a touring fingerstylist who bends and taps a guitar for two hours a night wants the same forgiveness at a much higher workload.
Compared to the alternatives
| MA540FX (this set) | Martin MA540 (standard) | Martin MA540T (coated) | D'Addario EJ16 | |
|---|---|---|---|---|
| Core construction | Thinner 'Flexible Core' SP wire under a heavier wrap | Standard tin-plated high-tensile steel core | Standard tin-plated high-tensile steel core | Standard hex steel core |
| Wrap alloy | 92/8 phosphor bronze | 92/8 phosphor bronze | 92/8 phosphor bronze + Lifespan 2.0 coating | 92/8 phosphor bronze |
| Gauge | .012–.054 Light | .012–.054 Light | .012–.054 Light | .012–.053 Light |
| Feel | Softer, easier to bend | Standard acoustic feel | Standard acoustic feel, slightly stiffer fresh | Standard acoustic feel |
| Best known for | Beginners and fingerstyle players who bend a lot; Tommy Emmanuel's touring set | Martin's factory-string default | Longer life for a small treble tradeoff | Taylor and spruce mid-body default |
Best for
- Fingerstyle players who bend notes constantly and want less finger fatigue across a long set or a full show
- Beginners still building calluses and hand strength, the exact player Martin engineered this construction for
- Martin dreadnought and OM owners who already like the standard MA540's tone and want an easier feel without changing gauge
- Touring or gigging players who restring often, since a fresh Flexible Core set feels broken-in faster than a stiffer standard core
Worst for
- Players chasing maximum stiffness and attack: the standard MA540 or a heavier Medium gauge gives more pushback under a hard flatpicking strum
- Anyone prioritizing string life over feel: step up to Martin's MA540T (Lifespan 2.0 coated) for meaningfully longer time between changes
- 12-string acoustic: Martin's Flexible Core 12-string variant is a separate SKU (MA500FX Extra Light), not this set
Verdict
MA540FX is Martin's standard phosphor bronze default with the edges softened. Same .012 to .054 Light gauge, same 92/8 phosphor bronze wrap, same in-house Martin manufacturing. The only real change is a thinner core wire that makes fretting and bending noticeably easier, which is exactly why Martin built it for beginners in the first place and exactly why a Grammy-winning fingerstyle virtuoso reaches for it before nearly every show, per Martin's own account of his routine. If you already like the standard MA540's tone but find fresh strings tough on your hands, or you're still building calluses, this is the same string with less resistance.
MA540FX Authentic Acoustic Flexible Core (.012–.054)
Why this one: Tommy Emmanuel's own touring set, per Martin's artist page and blog feature. Same gauge and alloy as the standard MA540, built to bend easier.
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