Martin SP Phosphor Bronze Light (.012–.054): the reference acoustic set
Reviewed by the Change Your Strings editorial team ·
Martin SP Phosphor Bronze Light (.012–.054) is the reference warm-and-woody acoustic set. Phosphor bronze wrap gives a rounder midrange than 80/20 bronze, better for folk, singer-songwriter, and fingerstyle where you want the guitar to breathe rather than sparkle. Light gauge is the safe default for a dreadnought or OM body; step down to custom light (.011) only if you're hybrid-strumming hard or have a smaller-bodied guitar.
Anatomy
- Model
- Martin SP Phosphor Bronze Light (MSP4100 series)
- Gauge
- .012 – .054 (Light)
- Gauge set
- .012, .016, .025, .032, .042, .054
- Core wire
- Tin-plated hex steel
- Wrap wire
- Phosphor bronze (copper alloyed with tin and trace phosphorus)
- Plain strings
- Tin-plated steel (.012, .016, sometimes .017 plain)
- Coating
- None, uncoated. For coated phosphor bronze, see Martin Lifespan
- Winding
- Standard roundwound
- Intended body shapes
- Dreadnought, OM, 000, Jumbo (light gauge fit). Custom Light (.011) for parlor / 00
- Intended tunings
- E standard primary; handles Drop D, DADGAD, Open G/D
- Tension behavior
- Light gauge is the factory-default setup tension for most production acoustics
- Launched
- Martin Studio Performance (SP) line introduced in the 1990s
- Package
- Single pack and multi-pack
Construction
- Core wire
- Tin-plated steel, hexagonal, consistent diameter.
- Wrap wire
- Phosphor bronze, copper alloyed with tin and a trace of phosphorus, which slows oxidation and adds midrange warmth vs. 80/20 bronze.
- Plain strings
- .012, .016 (sometimes .017), tin-plated steel, uncoated.
- Coating
- None in this set. For coated phosphor bronze, see Martin Lifespan.
Tone
Phosphor bronze lands in the middle of the acoustic tone spectrum: warmer than 80/20, brighter than silk-and-steel, more articulate than monel. It's the default answer for "what should I put on my acoustic?" because it flatters almost every playing style and body shape.
Best for
- Folk, singer-songwriter, fingerstyle acoustic. The warm midrange sits well under vocals.
- Drop D, DADGAD, Open G/D. Light gauge handles whole-step-down tunings without flapping.
- Dreadnought, OM, 000, jumbo bodies. These expect light-to-medium tension.
SP Phosphor Bronze Light
Why this one: The default acoustic set: warm phosphor-bronze midrange that flatters vocals, with light tension that handles Drop D and DADGAD.
Worst for
- Heavy-handed flatpicking on a dreadnought that wants to get loud. Go medium (.013–.056).
- Baritone acoustics. Need heavier specialized sets.
- Players chasing the brightest possible top end. 80/20 bronze or silk-and-bronze will do that better.
Who uses them
Martin SP Phosphor Bronze sets are used widely across singer-songwriter and folk. Specific artist attribution takes a primary-source citation; the line ships factory on most Martin acoustics from the D-28 down through the dreadnought lineup, so a working acoustic player who hasn't deliberately changed strings is likely already on this set.
Install notes
- Acoustic bridge pins can sit different depths, pull, straighten the ball end against the pin, then seat.
- Tune-stretch cycle 3–4 times; acoustics take longer to stabilize than electrics because the top is flexing too.
- Wipe down after play. Phosphor bronze browns fast with skin oils.
Related
- Match your tuning to a ranked pick: Folk in E Standard, Country in E Standard, Fingerstyle in DADGAD.
- Browse every string we've reviewed in by genre.