Acoustic guitar aficionados often find themselves in a similar position to the judge at a chili cook-off. With so many variations available on a simple theme, exercising discerning taste means paying attention to subtle differences.
The dreadnought, the gold standard design for the steel–string flat top, is built so similarly by so many manufacturers that players tend to look for minor differences that can account for substantive differences in quality.
And much like how the judge at the chili cook off may pay attention to the cut of beef used in the stew, dreadnought lovers will debate the merits of shoulder shape.
Some dreadnoughts feature squared shoulders, meaning the top of the body is flat, while others feature rounded or "sloped" shoulders, with a more gradual curve from the body to the neck.
This distinction in design is a subtle one, but a debate continues over whether shoulder shape is purely an aesthetic concern or a significant influence on a guitar’s performance.
A Mighty Guitar
Difference in dreadnought shoulder shapes actually stands as a good proxy for the rivalry between Martin and Gibson in the acoustic guitar arena.
Emerging around 1916, the dreadnought would become the most common steel string design. The guitar was named for its power, taking its moniker from a revolutionary battleship that first took to the seas in 1906, the HMS Dreadnought.
Martin owned the style, producing dreadnoughts that were larger and louder than any competitor’s designs at the time.
Martin made the first dreadnought for the Oliver Ditson Company. In 1931 Martin began offering dreads under its own name. The mahogany D–1 and the rosewood D–2 featured elongated, square–shouldered bodies and slotted pegheads.
Martin would set the dreadnought template three years later, releasing the D–18 and the D–28 in 1934. These were similar to the D–1 and the D–2, but elongated the neck to join the body at the 14th fret, as opposed to the 12th fret in the previous designs.
1934 was also the year that Gibson released its first dreadnought, the Jumbo. This dreadnought design was indebted to Martin’s but continued Gibson’s tradition of featuring rounded shoulders on steel string acoustics, like with its first flat top, the L–1.
In 1936 the Jumbo was replaced by two other round–shouldered dreadnoughts, the mahogany J–35 and the rosewood Advanced Jumbo.
For the most part, Martin’s dreadnoughts featured squared shoulders while Gibson’s featured rounded ones until the early 1960s. In 1960 and 1962, respectively, Gibson released their Hummingbird and Dove models, both of which featured dramatically squared shoulders.
Settling the Score
Some players prefer the look of a certain style of shoulder, but others believe that shape influences a guitar’s sound. The argument does that rounded shoulders lend clarity and balance by diffusing the overwhelming bass response associated with some dreadnoughts.
While this may be true of some guitars designed with rounded shoulders, there’s no scientific way to test this argument. After all, manufacturers don’t make two models of the same guitar that are identical on every count except for shoulder shape. There is no way, for instance, to hear what a mahogany D-18 with rounded shoulders sounds like in comparison to a conventional one with squared shoulders.
Perceived difference in performance likely has little to do with shoulder shape and a lot more to do with the the sum of construction differences. Martin’s and Gibson’s designs vary in many more ways than just shoulder design.
"Small differences in design add up to a noticeable difference in tone between a Gibson and a Martin, but not so much between a round-shoulder and a square-shoulder guitar."
Dana Bourgeois, the luthier behind Bourgeois Guitars, attributes much of the sonic distinctions to different bracing styles and scale lengths.
“Gibson bracing is tall, thin, light, and lightly mortised into lining. Martin bracing is more substantial all over and mortised more securely. Additionally, Martin dreads all have long scales while Gibson round shoulders, except for the Advanced Jumbo, have short scales.”
The guitar shop owner and historian Walter Carter agrees with this perspective. “Other small differences in design add up to a noticeable difference in tone between a Gibson and a Martin, but not so much between a round-shoulder and a square-shoulder guitar.”
Carter points out that a square-shouldered Hummingbird will sound more like the round-shouldered J-45 (of the same period) than a Martin D-18. He also notes that bridge design plays an important role.
“The bridge design and placement probably makes more difference than the body shape. On a Gibson with a reverse belly bridge, the bridge is about 2 3/4" from the soundhole. A Martin belly bridge is 3 1/8" away from the soundhole.”
Choosing Sides
Choosing between a square-shouldered or round-shouldered dreadnought is often conflated with choosing between a Martin– or Gibson–style guitar. And if you’re in the market for a dreadnought, there are some general tonal characteristics that can help guide your purpose.
“Martin dreads have a more powerful attack and higher headroom. Gibson round shoulders can have a sweet, rich, airy tone, though lack a certain punch.” Bourgeois says that the Martin style dreadnought’s powerful sound makes it the “traditional choice for bluegrass,” while the Gibson style is a better fit for a small ensemble or accompanying a singer (see Joey Ryan of The Milk Carton Kids).
Wood choice is obviously a top consideration as well. Carter points out that bluegrass pioneer Charlie Monroe played the mahogany-bodied, round-shouldered J-35 before adopting a Martin D-28, likely owing to the booming sound of its rosewood back and sides.
Carter adds, “Beyond bluegrass, it’s best to pay more attention to the tone than to the shoulders.” That’s a good rule of thumb for finding the dreadnought that’s right for you.