Unlike electric guitars, which rely heavily on the guitar’s pickups and amplification, the acoustic guitar’s body shape plays a pivotal role in its sound production. In the following article, we’re going to take a closer look at just how the shape of the body influences aspects of sound production. We’ll also list the most common body shapes and explain how their shape and dimensions influence the sound they produce.
Before we got too far into this article, I should point out while body shape, being the focal point of this article, plays a pivotal role in terms of the sound of an acoustic guitar it's important to understand there are many factors at play working holistically to influence the sound of an acoustic guitar. This includes the tonewoods the guitar is constructed from, the acoustic qualities of the room the guitar is being played in, the quality of the guitar's construction and perhaps most importantly the way a player holds and interacts with the guitar. For example, larger-bodied guitars tend to encourage forceful strumming, which naturally emphasizes lower frequencies, while the more intimate embrace of smaller guitars can lend itself to gentle fingerpicking, which can bring out higher tonal characteristics.
Harmonic Architecture
In the following section, we’ll take a closer look at the architecture of an acoustic guitar including body size, body shape, the soundboard, and bracing, and discuss how each of these components influences aspects such as volume, tone, articulation, responsiveness, resonance, and sustain.
Body Size
I’ve written fairly extensively on acoustic guitars over the years and in that time I’ve found the simplest way to explain the influence of body size is in terms of a room, in your house for example.
Think of it this way.
The size of the room is key to the guitar’s voice. Larger rooms, much like the internal dimensions of a large acoustic guitar body e.g. dreadnought or jumbo have more internal space, which allows for longer wavelength vibrations, correlating with lower frequencies. This expansive space creates a pressure differential with greater volume, enabling the sound to be more pronounced in the bass registers, contributing to a richer, deeper tone.
Alternatively, smaller-bodied guitars accentuate higher frequencies. Their more compact ‘rooms’ don’t allow lower frequencies to dominate, so what you hear is a sound that’s brighter and more articulate, all things being equal. It’s much like the difference between a bass-heavy home theater system and the clear, crisp articulation of studio headphones.
Smaller bodies often have a quicker response, making them ideally suited to fingerstyle playing, while larger bodies may have a more gradual response, ideal for strumming.
Body Shape
The shape of an acoustic guitar, characterized by the curves of the bouts and the waist, also plays a pivotal role in defining the sound produced. The bouts (the curved sections above and below the waist) are not only for visual symmetry; they also influence the guitar’s tonal character.
The lower bout, in particular, is integral to the shaping of the lower frequencies. Its size and shape determine how these frequencies resonate and project. The upper bout, while less influential, interacts with the sound emanating from the neck and fretboard, affecting the higher-end frequencies.
Meanwhile, the waist acts like a conduit.
A tighter more pronounced waist helps to articulate the separation between the lower and higher frequencies, providing clarity and definition to the guitar’s voice. A tighter waist also allows for a more focused projection of sound, often resulting in a tone that has a pronounced presence in the mid-range. This can be particularly beneficial for fingerpicking for example, as it provides great note separation.
In contrast, a more gentle curvature at the waist, such as that seen on the blockier dreadnought allows for a more even distribution of sound waves throughout the body, promoting a blend of bass and treble. This can create a fuller, more balanced sound, which is particularly desirable for rhythm guitar.
The Soundboard
The soundboard – the front of the guitar’s body – has the largest overall influence on tone, as the vibrations from the soundboard are largely responsible for the sound produced. You can think of a larger soundboard as more sluggish, in terms of resonance, due to its larger surface area. Because of this it naturally amplifies lower frequencies. Smaller soundboards are more agile, vibrating with the strings faster and accentuating higher frequencies as a result.
The Bracing
The bracing system of an acoustic guitar also plays a role in its sound quality, similar to the framework within a building that defines its structural integrity and acoustic properties. The bracing not only supports the soundboard but also intricately influences the tonal output. In larger guitars, the spacious interior allows luthiers to employ more elaborate bracing patterns. These patterns can be meticulously calibrated to enhance the resonance of lower frequencies, enriching the depth and warmth of the guitar’s tone.
In summary, the size and body shape of an acoustic guitar is a fundamental factor in defining its acoustic properties. The interplay between the physical dimensions of the guitar and the resultant sound is a testament to the intricate relationship between form and function in acoustic instruments. The luthier's craft involves balancing these elements to create instruments that not only appeal to the aesthetic sensibilities but also fulfill the tonal and ergonomic requirements of the guitarist.
The Most Common Acoustic Guitar Body Shapes
Now that we’ve discussed how the size, and shape of an acoustic guitar body influence the sound emanating from the guitar let’s take a closer look at the most common acoustic guitar body shapes. Many guitarists are unaware of what a dreadnought or concert-style guitar actually is, so if that’s you, the information below should be useful as it is an important consideration that goes well beyond mere aesthetics when choosing a new acoustic. I’ll also be producing articles for each of these body shapes in the near future.
| Body Shape | Design Notes |
|---|---|
Parlor | The sound of a parlor guitar is direct and focused, due largely to its body shape and size. The smaller soundboard and tighter waist of the parlor guitar mean that the strings’ vibrations are concentrated, producing a clear, precise tonal quality that emphasizes the mid and upper frequencies. Moreover, the reduced internal air volume limits the bass resonance, thereby preventing the sound from becoming too boomy. |
Concert (0) | The body shape and size of a concert guitar are designed to produce a well-rounded sound that emphasizes the midrange while still capturing sufficient bass and clear highs. Its dimensions allow for a larger soundboard compared to a parlor guitar, which translates into a greater resonance within the mid frequencies, making the concert guitar a more versatile instrument. The increased air volume inside the body provides a warmer tone than the parlor, with a more pronounced lower end, yet it maintains a balanced sound that does not become too boomy. |
Grand Concert (00) | The Grand Concert guitar offers a full, rich sound that retains balance and articulation. Its size, slightly larger than the concert, provides a comfortable middle ground for players looking for more volume and resonance without the bulk of a dreadnought. The body shape of the Grand Concert guitar, with its wider waist and slightly larger bouts, allows for an extended lower frequency response and increased volume, while still maintaining the clarity and focus for which smaller-bodied guitars are known. This size amplifies the guitar’s presence in the lower mids, creating a warm and enveloping sound. |
Auditorium (000) | The Auditorium guitar’s body shape is crafted to enhance projection and volume without the boominess that larger guitars often exhibit. The waist is pronounced enough to give clear definition, and the larger bouts boost the lower-mid frequencies. This results in a sound that has depth and complexity, allowing the lower notes to resonate fully without overshadowing the crisp, articulate highs. |
Orchestra Model (OM) | The Orchestra Model (OM) guitar, while sharing similarities with the Auditorium shape, stands out with its own distinct characteristics. The body size, similar to the Auditorium but with a slightly different bout and waist configuration, facilitates a sound that’s both clear and resonant. The longer scale length (compared to the 000) characteristic of the OM enhances string tension, which yields a more responsive feel and brighter treble tones. This tension, combined with the body’s shape, results in a balanced output that has a focused low end and pronounced mids, allowing each note to be articulated clearly. |
Dreadnought | The Dreadnought acoustic guitar is the go-to choice for guitarists seeking a bold, powerful sound that can fill a room or cut through a mix. With its large body and broad shoulders, the Dreadnought is particularly suited to bluegrass and country musicians who require volume and a strong bass response. The Dreadnought’s larger sound chamber, afforded by its wide waist and deep body, allows for significant air displacement, resulting in a voluminous tone with a pronounced low-end and rich overtones. The scale and scope of its body shape naturally emphasize bass frequencies, making the strumming of chords resonate with fullness and depth that smaller bodies cannot match. Additionally, the dreadnought’s size contributes to a sustain that is both long-lasting and warm. |
Square Shoulder Dreadnought | Sonically, the Square Shoulder Dreadnought retains much of the power and projection of its round-shoulder counterpart but with some distinct differences. The altered shoulder shape impacts the way sound waves interact within the guitar’s body, resulting in a tighter, more focused bass response and a pronounced midrange. The square shoulders also add a bit of extra punch to the treble frequencies, offering a brighter top-end that complements the strong bass and mid tones. |
Jumbo | The Jumbo acoustic guitar, with its grand and curvaceous body, is the largest of the common acoustic guitar shapes. The Jumbo’s substantial lower bout and deep sides create a significant internal air cavity, allowing for extensive vibration and a considerable enhancement of the lower frequencies. This results in a sonorous bass and a rich, full-bodied tonal spectrum. The size of the Jumbo guitar not only contributes to its volume but also to the sustain of each note, giving a lingering, enveloping quality to the sound. Despite the emphasis on the lower end, the design of the Jumbo does not forsake the highs, offering a balanced and clear treble response that complements the bass. |
Cutaways
The impact of a cutaway on an acoustic guitar’s sound is a topic of some debate. A cutaway refers to the section of the guitar’s body near the neck that is “cutaway” to allow easier access to the higher frets. While primarily a functional feature for playability, it does have some influence on the instrument’s acoustic properties.
From a construction standpoint, a cutaway slightly reduces the internal volume of the guitar’s body. In theory, this reduction could lead to a decrease in the lower frequency response and potentially affect the overall volume and projection of the guitar. The extent of this impact can vary depending on the size and shape of the guitar: on a larger-bodied instrument like a jumbo or a dreadnought, the effect of a cutaway might be negligible, while on a smaller-bodied guitar, the impact could be more pronounced.
However, the practical effect of a cutaway on sound would be minimal. The body shape and size are significantly more influential factors in determining the tonal qualities of an acoustic guitar. Additionally, many high-end acoustic guitars with cutaways are designed to compensate for any potential loss in sound quality, ensuring that the cutaway’s impact is virtually undetectable to the ear.
12 String Guitar Bodies
The body shape and size of a 12-string acoustic guitar are pivotal in shaping its characteristic choral sound, with the larger bodies of dreadnought or jumbo shapes typically being chosen to accommodate the added resonance and sustain from the instrument’s paired strings. These larger bodies provide the ample internal airspace needed for the complex harmonics and richer tones that are synonymous with 12-string guitars, while also offering a more substantial soundboard to bolster the lower frequencies against the shimmering highs.
12-string guitars also must contend with significantly greater string tension than their 6-string counterparts, necessitating a robust construction to maintain the guitar’s structural integrity. This tension can affect both the guitar’s tonality and its playability, with the increased pressure exerting more influence on the guitar’s top and overall sound projection. Smaller-bodied 12-strings, while less common, can deliver a more defined and articulate sound, but may not support the same full resonance as larger bodies.
Future Trends and Innovations in Acoustic Design
The acoustic guitar, steeped in tradition, is experiencing a renaissance in body design that marries time-honored craftsmanship with innovative technologies. As the industry leans into the future, sustainability becomes of increasing importance. Pioneers like Taylor Guitars are leading the charge, championing the use of responsibly sourced woods and alternative materials that promise longevity and environmental stewardship.
At the same time, the quest for enhanced sound quality drives luthiers to reimagine body shapes and internal structures, all in pursuit of that perfect harmony between the instrument and its artisanal heritage. This convergence of sustainability and acoustic excellence is sculpting a new era for the acoustic guitar body design, one that honors its past while boldly strumming into the future.
Innovations in acoustic guitar body design are increasingly focused on enhancing sound quality and playing comfort while integrating sustainable practices. Luthiers and manufacturers are experimenting with alternative materials such as bamboo, flax, and carbon fiber composites to create more eco-friendly guitars with unique acoustic properties. These materials not only offer environmental benefits but can also provide greater resistance to fluctuations in humidity and temperature, leading to more durable instruments. Furthermore, the exploration of non-traditional body shapes and bracing patterns aims to project a broader range of frequencies and increase resonance, offering players a wider palette of tonal possibilities.
Another burgeoning trend is the incorporation of smart technology directly into the guitar body. Some concepts even include built-in effects and looping controls, providing artists with new tools for creative expression without the need for external devices such as looping or effects pedals. As digital integration progresses, the acoustic guitar is poised to become a more versatile tool, catering to the modern musician’s demand for both traditional sound quality and cutting-edge technological convenience.
Final Thoughts
Keep in mind, that the acoustic guitar’s body shape is not just a matter of visual appeal; it’s the very essence of its voice and character. From the compact size and elongated body shape of a parlor guitar producing a clear, focused sound to the expansive resonance of a dreadnought enhancing bass frequencies for a rich, full-bodied tone, each shape carves out its unique sonic space. I hope the information above helps you make a more informed choice next time you are in the market for a new acoustic guitar.
