Wave speed and specific modulus compare material trends only within a model with matching geometry, boundaries and mode. They cannot alone predict onset, loudness or dynamic headroom. Elastic modulus measures stiffness, not failure strength. Individual samples, thickness, bracing, strings and excitation must be evaluated together.
Estimated reading time:
Wood selection for acoustic guitars should not stop at experiential judgments like “this wood sounds good.” Nor does the price of a wood show any engineering-level correlation with acoustic performance — it is driven by scarcity and market supply and demand. A more accurate understanding is: different parts of the guitar serve different functions, and therefore require different material parameters.
The soundboard must efficiently convert string energy into airborne sound; the back and sides act as an energy boundary, a reflective structure and a resonating shell; the neck is a structural member under long-term string tension; the fretboard and bridge emphasize hardness, wear resistance, stability and local energy transfer.
The core of wood selection for acoustic guitars is therefore not “expensive wood is always better,” but rather:
Using wood with matching parameters in the right position, and converting the material’s potential into a stable sonic outcome through thickness, bracing, radius, gluing and moisture control.
Contents
I. Core Parameters of Acoustic Guitar Woods
1. Density: ρ
Density is the most fundamental parameter, usually expressed in (kg/m^3).
Image source：Meyers Konversationslexikon, c.1885; artist unknown · Public domain
Density affects three aspects:
- Mass
- Resonant frequency
- Energy response speed
Faster energy transfer to the body may make some bands louder while accelerating string decay. Internal loss, bridge mechanical admittance and radiation loss act together; density, bridge mass or back-and-side species alone cannot predict sustain. Compare attack, spectrum and decay with matched strings, tuning, excitation and recording conditions.
For a soundboard, excessively high density is usually unfavorable, because a top needs to be “light and stiff.”
For back and sides, high density is not necessarily a drawback, since they are not mainly responsible for radiating sound directly, but act more like an energy boundary.
2. Young’s modulus: E
Young’s modulus describes a material’s ability to resist tensile or bending deformation, usually expressed in (GPa).
Image source：Nicoguaro · CC0
Wood is a strongly anisotropic material its stiffness varies greatly between directions:
- Along the grain: (EL)
- Radial direction: (ER)
- Tangential direction: (ET)
(EL) is usually far higher than (ER) and (ET).
For a guitar soundboard, stiffness along the grain is critical, because the strings apply continuous tension and dynamic excitation through the bridge. Insufficient grain-direction stiffness makes the top prone to collapse, sluggish in response and limited in dynamic ceiling.
3. Specific modulus:
The specific modulus is a key indicator for judging soundboard woods:
It expresses “how much stiffness is provided per unit of mass.”
For a soundboard, the ideal material is neither simply high stiffness nor simply low density, but:
This is the core reason why spruces have long been the mainstream soundboard material. Spruce can usually provide high grain-direction stiffness at relatively low density, and therefore offers high acoustic efficiency.
4. Speed of sound: c
In a simplified model, the speed of sound along the grain in wood can be approximated as:
where:
- (CL): speed of sound along the grain
- (EL): Young’s modulus along the grain
- (ρ): density
Wave speed and specific modulus compare material trends only within a model with matching geometry, boundaries and mode. They cannot alone predict onset, loudness or dynamic headroom. Elastic modulus measures stiffness, not failure strength. Individual samples, thickness, bracing, strings and excitation must be evaluated together.
5. Mechanical impedance: Z
For a one-dimensional longitudinal travelling wave, material characteristic impedance is z = ρc = √(Eρ), in Pa·s/m, for a specified direction and model. This differs from frequency-dependent bridge mechanical impedance Z_b(ω) = F(ω)/v(ω), in N·s/m. The former does not directly predict how a plate responds or “reflects tone”; geometry, support, modes, loss and air coupling also matter.
6. Acoustic radiation coefficient: R
The radiation ratio R = c/ρ = √(E/ρ³) is a material-selection index, not dimensionless whole-guitar energy conversion efficiency. Its units are m⁴/(kg·s); specify the direction of E and measurement conditions. A specimen index cannot directly predict a finished guitar's loudness, sustain or quality. Actual plate radiation efficiency also depends on size, thickness, mode shape, wavelength and coupling.
7. Internal damping: η
Internal damping describes a material’s ability to convert vibrational energy into heat.
A common approximation is:
where:
- (Q): quality factor
- (η): loss factor or damping coefficient
High damping makes the sound decay faster and flattens peaks; it may feel softer, warmer and less harsh.
Low damping gives longer sustain, clearer highs and a more open dynamic range, but can also make the sound sharper or harder to control.
For a soundboard, low damping is generally desirable — but lower is not always better. Too little damping may overemphasize local peaks and make the sound uneven.
II. Wood Selection Logic for Different Parts
1. Soundboard: the goal is “light, stiff, low damping, high efficiency”
The soundboard is the main sound-producing component of an acoustic guitar. String vibration enters the top through the bridge, and the top then drives the air to create sound.
Image source：Achim Raschka · CC BY-SA 3.0
The core goals for a soundboard are:
| Parameter | Requirement |
|---|---|
| Density | Lower |
| Grain-direction modulus | Higher |
| Specific modulus | High |
| Speed of sound | High |
| Damping | Lower |
| Cross-grain stiffness | Sufficient |
| Stability | High |
| Crack risk | Low |
The basic judgment formula for a soundboard can be simplified as:
This is also why spruces have long dominated the mainstream soundboard position.
Common soundboard woods
Spruce, cedar, rosewood, mahogany, maple and walnut are common candidates. Names and traditional uses guide a shortlist, but do not specify a sample’s acoustic parameters or guarantee a tone. Measure individual pieces and compare them within the structural design.
Why can’t you judge a soundboard by its grain lines alone?
Even, straight, quarter-sawn grain is an important indicator, but not the whole picture, because the sonic outcome is determined by several parameters together:
where:
- (f): modal frequency of the plate
- (h): thickness
- (E): elastic modulus
- (ρ): density
Note that thickness (h) has a large effect on frequency. More completely, the bending stiffness of a plate can be approximated as:
where:
- (D): bending stiffness
- (E): Young’s modulus
- (h): thickness
- (ν): Poisson’s ratio
Thickness has a cubic effect:
This means:
for the same piece of wood, differences in thickness may change the sound more directly than differences between species.
So soundboard selection must not rely only on “species” and “grain”; it must combine density, stiffness, thickness, bracing and the target tone.
2. Back and sides: the goal is “stability, reflection, tonal coloring, boundary conditions”
The back and sides are not the main sound source, but they influence the boundary conditions of the sound, energy reflection, resonance behavior and sustain characteristics.
The tasks of the back and sides include:
- Forming the structural shell of the body
- Constraining the movement of the top
- Reflecting part of the sound energy
- Participating in low-frequency coupling
- Providing a degree of tonal coloring
The priorities for back and sides therefore differ from those of the top.
| Parameter | Requirement |
|---|---|
| Density | Medium-high density is common |
| Impedance | Can be relatively high |
| Damping | Chosen according to the target sound |
| Stability | High |
| Bending workability | Good |
| Cracking risk | Low |
| Appearance | Important |
Common back and side woods
Spruce, cedar, rosewood, mahogany, maple and walnut are common candidates. Names and traditional uses guide a shortlist, but do not specify a sample’s acoustic parameters or guarantee a tone. Measure individual pieces and compare them within the structural design.
Image source：Philipp Zinger · CC BY-SA 3.0
Image source：Philipp Zinger · CC BY-SA 3.0
The relationship between back/sides and top
An acoustic guitar can be simplified into a coupled system:
The top handles the main energy conversion; the back and sides influence how energy is retained, reflected and dissipated.
If the back and sides have low damping and high density, the sound may have more sustain and complex overtones.
If their damping is higher, the sound may be more direct, clean and recording-friendly.
This is why rosewood is often described as “complex, rich in overtones, deep in the lows,” while mahogany is often described as “direct, mid-forward, clean.”
3. Neck: the goal is “bend-resistant, torsion-resistant, long-term stable”
The neck is not a main sounding plate, but a structural member that bears string tension over the long term.
The total string tension of a steel-string acoustic guitar typically reaches tens of kilograms. The neck must resist over the long term:
- Tension along the strings
- Bending deformation
- Torsional deformation
- Humidity changes
- Creep
- Glue-joint stress between fretboard and neck
Key indicators for neck materials:
| Parameter | Requirement |
|---|---|
| Grain-direction stiffness (EL) | High |
| Shear modulus (G) | High |
| Density | Should not be too high |
| Stability | Very high |
| Shrinkage rate | Low |
| Torsional resistance | High |
| Workability | Good |
Bending resistance correlates strongly with material stiffness and section depth. In a simplified beam model, the bending stiffness is:
where:
- (E): Young’s modulus of the material
- (I): second moment of area of the section
For a rectangular cross-section:
where:
- (b): width
- (h): thickness or height
This shows that a neck’s bending resistance depends not only on the wood, but strongly on the neck’s cross-section design.
Common neck woods
Spruce, cedar, rosewood, mahogany, maple and walnut are common candidates. Names and traditional uses guide a shortlist, but do not specify a sample’s acoustic parameters or guarantee a tone. Measure individual pieces and compare them within the structural design.
Neck selection should not chase lightness alone. A neck that is too light but insufficiently stiff leads to long-term action changes, fret buzz, twisting and drifting feel.
Image source：Stephen Ondich · CC BY-SA 3.0
A more reasonable goal is:
that is, sufficient bending and torsional resistance per unit of weight.
4. Fretboard: the goal is “hard, wear-resistant, stable”
The fretboard directly endures long-term friction and local pressure from fingers, frets and strings. Its acoustic influence exists, but durability and stability take priority.
Key considerations for fretboard materials:
| Parameter | Requirement |
|---|---|
| Janka hardness | High |
| Density | High |
| Wear resistance | High |
| Dimensional stability | High |
| Shear stiffness (G) | High |
| Gluing reliability | Good |
| Surface feel | Good |
Common fretboard materials:
The fretboard’s influence on sound is more like “boundary refinement” than a core sound source. It may alter the attack, clarity and local damping, but it does not define the instrument’s main acoustic character the way the top does.
5. Bridge: a small part with a big influence
Although small, the bridge sits at the energy input point — the key component through which string vibration enters the top.
Image source：Elmschrat · CC BY-SA 4.0
The bridge’s core functions:
- Transferring string energy
- Providing local mass
- Changing the top’s stiffness around the bridge
- Affecting high-frequency response
- Affecting onset speed
A too-heavy bridge reduces the top’s sensitivity:
where:
- (f): system resonant frequency
- (k): equivalent stiffness
- (m): equivalent mass
When the bridge mass (m) increases, the resonant frequency drops, the response may slow down and the highs may decrease.
Bridge materials therefore usually need:
| Parameter | Requirement |
|---|---|
| Hardness | High |
| Density | Medium-high, but not too heavy |
| Gluing performance | Good |
| Stability | High |
| Crack resistance | Good |
Common materials include rosewood, ebony and African blackwood. Ebony is harder and heavier; rosewood is relatively lighter with different damping characteristics. The final choice must combine top thickness, bracing and target response.
III. How Wood Parameters Affect Sound
Wood parameters mostly shape the tone through modal behavior. For more detail, see the related articles here and here (or click the card links below).
This article does not go deep into modal theory; it keeps more natural language so that more readers can follow and understand.
1. Response speed
Response speed mainly relates to the top’s mass, stiffness and damping.
Image source：MikeRun · CC BY-SA 4.0
Roughly speaking:
Soundboards with low density, high specific modulus and low damping are usually easier to excite with a light touch.
This is why Engelmann spruce and Western red cedar are often considered responsive to a light touch, while Adirondack spruce needs stronger excitation to fully open up, in exchange for a higher dynamic ceiling.
2. Dynamic ceiling
The dynamic ceiling can be understood as: as playing force increases, can the sound stay clear, stable and uncompressed?
A high dynamic ceiling usually requires:
Adirondack spruce is often used for high-dynamics playing because its stiffness and strength perform well, and it does not compress too early under heavy strumming.
Cedar tops respond quickly to a light touch, but under strong force they compress more easily and lose definition.
3. Sustain
Sustain relates to the system’s energy loss.
Image source：Jahobr · Public domain
In simplified terms:
Low damping means slow energy decay and longer sustain.
High damping consumes energy faster; the sound is shorter and cleaner.
Species differ in distributions of density, stiffness and loss, with substantial variation within a species. Words such as “warm” or “rich in overtones” are listening descriptions, not guaranteed material outcomes. The back and sides also participate through structural and air coupling; high-density “reflection” versus low-density “absorption” is not a sufficient model. Evaluate the instrument with thickness, bracing, boundaries, strings and measured response.
4. High-frequency brightness
High-frequency behavior relates to multiple factors:
Image source：Geek3 · CC BY 3.0
- Soundboard stiffness
- Bridge mass
- Soundboard damping
- Finish-film damping
- Back-and-sides reflection
- Local boundary conditions of neck and fretboard
Low-damping materials preserve high-frequency detail more easily:
But too many highs do not equal a good sound. If certain modal peaks are too strong, the result can be harsh, thin and piercing. Good design is not simply chasing “brightness,” but controlling spectral balance.
5. Tonal complexity
Tonal complexity usually comes from the coupling between multiple modes:
Rosewood back and sides often bring richer overtones; mahogany and maple can make the sound more focused and direct.
Complexity is not an absolute advantage. In recording, sing-along and ensemble contexts, too many overtones may occupy spectral space; in solo and fingerstyle contexts, rich overtones may enhance expressiveness.
IV. Common Wood Combinations and Use Cases
Spruce, cedar, rosewood, mahogany, maple and walnut are common candidates. Names and traditional uses guide a shortlist, but do not specify a sample’s acoustic parameters or guarantee a tone. Measure individual pieces and compare them within the structural design.
Image source：Lilla Frerichs · CC0
V. Wood Selection Process in Guitar Making
1. Soundboard screening
Grading tops by visual inspection alone is not recommended. A more reliable process is:
Image source：suvajack · CC BY 2.0
- Measure weight
- Measure dimensions
- Calculate density
- Tap or excite to measure frequency
- Measure deflection
- Judge grain-direction and cross-grain stiffness
- Check grain, knots, cracks and runout
- Decide thickness and bracing strategy according to the target model
Top grading should serve concrete product goals.
Heavy-strumming guitars and light-touch fingerstyle guitars should not use exactly the same grading logic.
2. Back and sides screening
For back and sides, focus on:
- Stability
- Crack risk
- Bending workability
- Density
- Damping tendency
- Visual grade
- Sustainability and compliance
For back and sides, harder is not necessarily better, and heavier is not necessarily better. For mass production, stability and processing yield matter a lot.
3. Neck screening
Neck grading should lean more structural:
Image source：Mr. Littlehand · CC BY 2.0
Key checks:
- Whether the grain is straight
- Whether there is obvious sloping grain
- Whether there is warping risk
- Whether there is internal stress
- Whether it is fully dried
- Whether it suits lamination or carbon-fiber reinforcement
- Whether it stays stable after humidity cycling
For the neck, sonic gains must yield to structural reliability. After-sales problems from neck deformation far outweigh gains from tiny tonal differences.
VI. Moisture Content and Stability
Wood parameters must be discussed at a specific moisture content. At different moisture levels, density, stiffness, damping and dimensions all change.
Image source：Hrco · CC BY-SA 4.0
The equilibrium moisture content (EMC) of wood is determined by ambient temperature and humidity. A common goal in guitar making is to let the wood stabilize under conditions close to its usage environment.
If workshop humidity control is unstable, the result can be:
- Soundboard cracking
- Back and sides shrinking
- Neck deformation
- Fretboard shrinkage causing fret sprout
- Increased bridge gluing risk
- Seasonal action changes
Wood selection must therefore be considered together with humidity management.
Empirically, acoustic guitar production environments should usually be kept within a relatively stable temperature and humidity range. For example:
| Item | Recommendation |
|---|---|
| Relative humidity RH | Around 40%–50% |
| Temperature | Stability first |
| Wood intake | Record batch, weight, moisture content |
| Before machining | Fully condition (acclimatize) |
| Before gluing | Avoid short-term humidity swings |
| Before shipment | Re-inspect stability |
Dimensional changes in wood are directional:
This is why tops and backs usually emphasize quarter-sawing. Quarter-sawn material is more stable across the width, straighter in grain, with lower deformation risk.
Kepma Wood Equilibrium Moisture Content (EMC) Visualization Tool
Enter temperature and relative humidity
Temperature is entered in degrees Celsius °C, relative humidity in percentages %. The horizontal axis is relative humidity RH; the vertical axis is EMC, i.e. the equilibrium moisture content based on oven-dry mass.EMC curve
The curve shows how the equilibrium moisture content of wood changes with relative humidity at a given temperature.Mathematical model: Hailwood–Horrobin equation
1. EMC main equation
Let h = RH / 100 be the decimal form of relative humidity. Then:
EMC(T, h) = (1800 / W) × [ (k × h) / (1 - k × h)
+ (k1 × k × h + 2 × k1 × k2 × k² × h²)
/ (1 + k1 × k × h + k1 × k2 × k² × h²) ]
2. Coefficients W, k, k1, k2, with T in degrees Celsius
W = 349 + 1.29 × T + 0.0135 × T²
k = 0.805 + 7.36e-4 × T - 2.73e-6 × T²
k1 = 6.27 - 9.38e-3 × T - 3.03e-4 × T²
k2 = 1.91 + 4.07e-2 × T - 2.93e-4 × T²
3. Meaning of the symbols
- EMC: Equilibrium Moisture Content, expressed in %.
- T: ambient temperature, in °C.
- RH: ambient relative humidity, in %.
- h: the decimal form of relative humidity; for example, at RH = 50%, h = 0.50.
- W, k, k1, k2: temperature-dependent empirical fitting coefficients.
- First term: dissolved water in the model.
- Second term: hydrated water in the model.
VII. The Principle of Heat Treatment
Heat-treated wood, often called torrefied or roasted wood, is produced by thermally treating wood in a low-oxygen environment, altering some of its volatile components and hemicellulose.
Image source：Stephen Ondich · CC BY-SA 4.0
Heat treatment may bring:
- Reduced moisture sensitivity
- Improved dimensional stability
- Slightly lower density
- Possible improvement in sound speed and specific modulus
- Possibly lower damping
- Darker color
- Possibly increased brittleness
It can be simplified as:
This can be favorable for a top, as it may bring faster response and the dry character associated with an “aged” instrument.
But heat treatment is not an unconditional upgrade. Excessive heat treatment may cause:
- Increased brittleness
- Changed gluing risk
- Reduced crack resistance
- Thinner sound
- Reduced structural safety margin under high dynamics
VIII. Material Priorities for Different Parts
More specifically:
Image source：Larry Jacobsen · CC BY 2.0
- Soundboard: prioritize (E/ρ), damping, sound speed, grain stability
- Back and sides: prioritize stability, density, damping, bending workability
- Neck: prioritize bending resistance, torsional resistance, low deformation, low creep
- Fretboard: prioritize hardness, wear resistance, stability
- Bridge: prioritize hardness, mass, gluing performance, energy-transfer efficiency
IX. Common Misconceptions in Wood Selection
Misconception 1: Expensive wood always sounds better
Not true.
Expensive wood may be scarce, beautiful and steeped in tradition, but that does not mean it is necessarily better suited to a particular guitar. The sonic outcome comes from the joint action of material and structure.
Wood is only one of the input variables.
Misconception 2: Judging by species only, ignoring individual plate variation
Variation within a single species can be large. Two Sitka spruce plates may differ significantly in density, stiffness and damping.
Image source：G-Lignum · CC0
A more reliable approach is to measure each plate individually, rather than judging by the species label.
Misconception 3: The thinner the top, the better
A thinner top increases sensitivity, but also reduces the structural safety margin.
Since bending stiffness follows:
A slight reduction in thickness noticeably reduces stiffness. An overly thin top may sound open in the short term, but over time is prone to collapse, deformation and insufficient dynamics.
Misconception 4: Back and sides must be as hard and heavy as possible
Not necessarily.
Species differ in distributions of density, stiffness and loss, with substantial variation within a species. Words such as “warm” or “rich in overtones” are listening descriptions, not guaranteed material outcomes. The back and sides also participate through structural and air coupling; high-density “reflection” versus low-density “absorption” is not a sufficient model. Evaluate the instrument with thickness, bracing, boundaries, strings and measured response.
Misconception 5: The neck wood mainly determines the tone
The neck wood does affect sound, but structural stability matters more. For mass production and after-sales, the neck's bending resistance, torsional resistance, drying and dimensional stability outweigh subtle tonal differences.
X. Practical Wood Selection Advice
1. If the goal is an all-round steel-string guitar
Recommended direction:
- Soundboard: Sitka spruce
- Back and sides: East Indian rosewood / mahogany / walnut
- Neck: mahogany or a stable alternative
- Fretboard: ebony, rosewood, pau ferro
The logic:
Sitka spruce is forgiving, with a wide dynamic range, suiting strumming, sing-along and fingerstyle. Paired with rosewood the sound is richer, with mahogany more direct, with walnut more balanced.
2. If the goal is heavy strumming, bluegrass and big dynamics
Recommended direction:
- Soundboard: Adirondack spruce
- Back and sides: rosewood or mahogany
- Body: Dreadnought or large body
- Bracing: ensure structural support and dynamic headroom
The logic:
Adirondack spruce has a high dynamic ceiling and does not compress easily under strong excitation.
3. If the goal is light-touch fingerstyle
Recommended direction:
- Soundboard: Engelmann spruce, European spruce, Western red cedar, redwood
- Back and sides: rosewood, walnut, koa
- Body: OM, GA, small jumbo, etc.
The logic:
Light-touch fingerstyle needs a low onset threshold, rich detail and good sustain. The top should not be too thick, and the bridge mass must be controlled.
4. If the goal is recording-friendliness
Recommended direction:
- Soundboard: Sitka spruce, European spruce, redwood
- Back and sides: mahogany, walnut, maple
- Control overtone complexity
The logic:
In a recording environment, too much low end and too many overtones can be hard to mix. A more direct, focused sound is easier to place into a track.
5. If the goal is stable mass production
Recommended direction:
Image source：B137 · CC BY-SA 4.0
- Soundboard: reliably supplied Sitka or European spruce, or proven alternatives
- Back and sides: mahogany-type woods, sapele, walnut, stable rosewood
- Neck: stable mahogany, sapele, maple, laminated construction
- Fretboard: sustainably supplied ebony substitutes, rosewood substitutes, engineered materials
XI. The Essence of Wood Selection Is System Matching
The essence of wood selection for acoustic guitars is not the search for some “magical wood,” but the establishment of a parameterized judgment system.
Image source：Richard · CC BY-SA 2.0
The top should be light, stiff, low-damping and efficient; the back and sides stable, reflective and tonally coloring; the neck bend-resistant, torsion-resistant and deformation-free over time; the fretboard hard, wear-resistant and stable; the bridge balanced between mass, hardness and energy transfer.
In one sentence:
The top determines how energy is excited, the back and sides determine how it is retained and shaped, the neck determines whether the system stays stable over time, and the fretboard and bridge determine the local boundary conditions and playing-feel details.
The most reliable method of wood selection in guitar making is not relying on species names and experiential adjectives, but building a data closed loop:
Only when material parameters, structural design and real testing form a closed loop does wood selection turn from empiricism into a replicable engineering capability.
Text version of this page
Two further readings embedded in this article
The full content of two site articles is embedded in the body of this article as further reading on this topic.
The first is “Fundamentals of Guitar Modal Concepts,” which introduces the basic concepts of modes, Chladni patterns of circular plate vibration, the meaning of nodal lines and antinodes, and the relation between natural frequency, Young's modulus and density, with an interactive circular-plate mode-shape simulator.
The second is “Acoustic Modeling of the Guitar as a Coupled Vibrating System,” which discusses how the guitar is not a simple superposition of single oscillators but a coupled vibrating system of top, back and body air cavity, and covers how coupling affects frequency and response and how to handle it in modeling.
Together with this article, the two pieces form one thread: from wood selection and parameters, to the modal behavior of the top, to the acoustic response of the coupled whole instrument. Suggested order: this article, modal fundamentals, coupled modeling.
The Hailwood–Horrobin equation estimates equilibrium moisture content as a percentage of oven-dry mass. It is not a measurement of the wood's present moisture or a prediction of equilibration time. The first term represents dissolved water and the second hydrated water in this model; their descriptions must not be reversed. Species, adsorption/desorption history, heat treatment and moisture gradients can cause differences. The curve alone does not certify a particular board ready for machining.
Faster energy transfer to the body may make some bands louder while accelerating string decay. Internal loss, bridge mechanical admittance and radiation loss act together; density, bridge mass or back-and-side species alone cannot predict sustain. Compare attack, spectrum and decay with matched strings, tuning, excitation and recording conditions.
Checks and conditions
| Item | Correct interpretation | Practical check |
|---|---|---|
| Soundboard | Density, directional stiffness and damping | Evaluate thickness and bracing; species does not guarantee tone |
| Back and sides | Structural vibration and air coupling | Density or reflection alone cannot predict sustain |
| Neck, fingerboard and bridge | Stiffness, dimensional stability, mass and bonding | Select for each component and its structural loads |
| Humidity and moisture content | Ambient relative humidity is not wood moisture content | An equilibrium model is not a moisture-meter reading |
Sources and further reading
Species differ in distributions of density, stiffness and loss, with substantial variation within a species. Words such as “warm” or “rich in overtones” are listening descriptions, not guaranteed material outcomes. The back and sides also participate through structural and air coupling; high-density “reflection” versus low-density “absorption” is not a sufficient model. Evaluate the instrument with thickness, bracing, boundaries, strings and measured response.
The ideal-string formula assumes uniform linear density, constant tension, small amplitude and fixed ends, neglecting bending stiffness. Wound-string density cannot simply be calculated as ρA for a homogeneous cylinder. Fretting stretch, end compliance, compensation and inharmonicity also affect frequency. This model explains trends rather than completely predicting intonation or playing feel.
