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Your data is stored securely and used solely for educational purposes. Unauthorized use, reproduction, or disclosure of this application, its curriculum, or its content is strictly prohibited.
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Your data is stored securely and used solely for educational purposes. Unauthorized use, reproduction, or disclosure of this application, its curriculum, or its content is strictly prohibited.
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Acoustic analysis lab — record precision measurements during each build phase.
01Material grading — soundboard
Measure on the thicknessed plate before bracing
Cost:
g
××mm
How to obtain this — mass, dimensions & density
| 1. | Thickness the soundboard plate to final dimension first — density and stiffness both depend on it, and bracing changes the numbers. |
| 2. | Weigh the bare plate on a gram scale (0.1 g resolution). Record as Mass. |
| 3. | Measure length and width with calipers at the widest points; measure thickness at the center of the lower bout. Record as Dimensions — density auto-calculates. |
Density should land roughly 340–460 kg/m³ for spruce, 380–600 kg/m³ for cedar. Well outside that range usually means a measurement error rather than an unusual plate.
kg/m³
mm Load:kg
GPa
How to obtain this — deflection & stiffness (for Young's modulus)
| 1. | Support the plate as a simple beam: rest both ends on supports spaced a fixed distance apart (note the span in your bench notes — it matters for the calculation). |
| 2. | Hang a known weight at the center and measure the center-point sag with a dial indicator or calipers against a straightedge. Record as Longitudinal deflection and Load. |
| 3. | Calculate E from beam deflection theory (E = (span³ × load) / (4 × width × thickness³ × deflection), adjusted for your units) and enter it as Young's modulus — radiation ratio auto-calculates from E and density. |
Taps the bare plate to measure how it resists bending along the grain, across the grain, and twisting. Together the three readings capture the wood's real stiffness and shear properties — enough to calculate Young's modulus, shear modulus, and a recommended thickness for this plate.
Black = hold • Red = tap
Hz
Hz
Hz
GPa
GPa
02Component mass tracking
Precision to 0.1 g for accurate mass profiling
| Component | Target (g) | Actual (g) |
|---|
How to obtain this — component masses
| 1. | Weigh each component on a gram scale (0.1 g resolution) right before it gets glued into the assembly — once joined you can't separate it again. |
| 2. | Set Target from your plan or a reference build before you start cutting; fill in Actual as each piece is weighed. |
| 3. | Internal bracing auto-fills a reference Target once a bracing pattern is picked in §03. Bridge plate and Finished bridge each get a material dropdown that auto-fills a reference Target from that wood's density — pick one to see the number, then adjust it by hand if your build differs. |
| 4. | M_e (total effective mass) is the sum of the components that move with the top when it vibrates — typically the top plate, braces, and bridge. Add these as you go rather than waiting until the end. |
Large swings between Target and Actual are useful diagnostic signals — they tell you where the build is running heavy or light before you're committed.
03Structural stiffness (K_e)
Measure after bracing is glued and final-carved
mm underkg
N/mm
How to obtain this — center-point stiffness (K_e)
| 1. | Support the braced top at the edges the way it will sit in the finished body — free at the center, supported around the perimeter (a simple jig or the rim itself works). |
| 2. | Apply a known weight at the center of the lower bout (directly over where the bridge will sit) and measure how far the center deflects with a dial indicator or calipers against a straightedge. |
| 3. | Record the deflection as Center point deflection and the weight as the load — K_e (stiffness) auto-calculates as load ÷ deflection. |
Measure this before final voicing and again after, if you thin or re-brace — K_e is one of the clearest before/after indicators of how much a voicing pass actually changed the plate.
04Resonance mapping — 4-DOF scan
Tap-test on the closed box
| Mode | Description | Hz | Note | Target |
|---|
Reference targets — Gore & Gilet (standard body)
| Mode | Target Hz | Note | Guidance |
|---|---|---|---|
| T(1,1)1 — Air | 95–105 Hz | G2–Ab2 | Controlled by body volume & sound hole size |
| T(1,1)2 — Top | 185–210 Hz | F#3–Ab3 | Lower by thinning or voicing braces |
| T(1,1)3 — Back | 220–250 Hz | A3–B3 | Influenced by back thickness & bracing |
| Mode gap | 500–900 cents | 3rd–6th | Closer = more even response across register |
Using the Target field: Enter your voicing goal or a build stage note — e.g. "aim for 100 Hz, check after closing box" or "voice X-brace to lower by ~10 Hz". Absolute numbers matter less than the relationship between modes. A well-matched pair close together in a musically useful interval produces balanced projection and even response.
05Final voicing audit
Hz
Hz
How to obtain this — monopole mobility & dipole frequencies
| 1. | Tap-test the closed box near the bridge (monopole excitation point) and listen/feel for how freely the top moves — "High" responsiveness feels lively and loud at low tap force; "Low" mobility feels stiffer but holds together better at high playing volume. This is a judgment call backed by the tap, not a numeric reading. |
| 2. | Find the cross- and long-dipole modes by tapping near the edges of the lower bout (cross-dipole) and near the waist (long-dipole) while watching a tuner or spectrum analyzer app — record the frequency where each peak shows up. |
How to obtain this — wolf note check
| 1. | Play a chromatic scale up the neck on the fundamental string(s) near the body's main air/top resonance range, listening for any note that suddenly chokes, beats, or jumps in volume — that's a wolf note. |
| 2. | If one shows up, identify it (e.g., "A3") — a wolf usually means a structural resonance is sitting right on top of a played note rather than safely between notes. |
06Chladni pattern logger
Sketch and describe nodal patterns at each resonance mode
For each mode, select the mode label, log the Hz, sketch the nodal pattern on the grid, and add a written description.
How to obtain this — Chladni patterns
| 1. | Sprinkle a thin, even layer of fine glitter or semolina across the plate or assembled top. |
| 2. | Drive the plate with a speaker/exciter (or careful sine-sweep tap) at the Hz value found in §04 for the mode you're logging — sweep slowly through it to find the exact frequency where the pattern locks in sharpest. |
| 3. | At resonance, the loose material collects along the node lines (where the surface stays still) and clears from the antinodes (where it moves most). Photograph or sketch the pattern, then enter the mode label, Hz, and a short description below. |
Patterns are most legible once the box is fully assembled and closed — earlier in the build (bare plate) they'll look different and aren't directly comparable to the §04 closed-box targets.
07Before / after voicing comparison
Log K_e and resonance at rough brace, post-carve, and post-assembly
Track how stiffness and key resonances shift through each voicing stage. Deltas are calculated automatically from rough brace to post-assembly.
| Measurement | Rough brace | Post-carve | Post-assembly | Δ Total |
|---|---|---|---|---|
| K_e (N/mm) | — | |||
| T(1,1) Hz | — | |||
| T(2,1) Hz | — | |||
| Mass (g) | — |
08Radiation ratio benchmarking
Compare your R against reference species ranges
Your radiation ratio (R = √(E ⁄ ρ³)) from Section 01 is plotted against typical ranges for common soundboard species. Higher R generally means more efficient sound radiation relative to mass.
Your R value (auto from §01):
—
or override manually:
Reference ranges
| Species | R min | R max | Character |
|---|---|---|---|
| Engelmann Spruce | 11.5 | 13.5 | Warm, responsive, low headroom |
| Sitka Spruce | 10.5 | 12.5 | Balanced, strong, wide dynamic range |
| Western Red Cedar | 10.0 | 12.0 | Dark, immediate, fingerstyle-friendly |
| European Spruce | 11.0 | 13.0 | Classic, focused, complex overtones |
| Redwood | 10.5 | 12.0 | Rich, complex, cedar-like response |
09Setup & playability
Final setup measurements on the strung instrument
mm @ 7th fret
How to obtain this — neck relief
| 1. | Capo the 1st fret and fret the string at the body joint fret. |
| 2. | Measure the gap between string bottom and fret top at the 7th fret with a feeler gauge — that is the relief. |
| 3. | Typical starting range: 0.1–0.2mm for light fingerstyle, up to ~0.3mm for heavy strumming. |
| Treble side | Bass side | |
|---|---|---|
| Nut action (1st fret) | ||
| 12th-fret action |
mm above bridge
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