# Tuning Notes — Modular Pedestal Drum Stack ## Acoustic targets | Drum | OD (mm) | Target note | Target Hz | Predicted T (N/m) | Predicted first overtone (Hz) | |------|---------|-------------|-----------|-------------------|-------------------------------| | 1 | 300 | A2 | 110.00 | 425 | 175.3 | | 2 | 250 | C3 | 130.81 | 419 | 208.5 | | 3 | 200 | E3 | 164.81 | 426 | 262.7 | | 4 | 150 | G3 | 196.00 | 343 | 312.4 | | 5 | 100 | A3 | 220.00 | 215 | 350.6 | Predictions from `modular-pedestal-drum-stack-starter.wl` for an ideal circular membrane under uniform tension. Real drums diverge in three predictable ways: 1. **Air-load drop** — a head with open shell below it drops ~2–3% in fundamental relative to the ideal-membrane prediction. Account for this by tensioning ~3% above target before final adjustment. 2. **Stiffness rise** — mylar has finite bending stiffness, which raises the fundamental by 1–2% over the ideal prediction. Partially cancels (1). 3. **Per-rod tuning variance** — even with a drum dial, rod-to-rod tension varies ±5 cents around the rim. The audible pitch sits at the mean; sharp spots ring slightly out. Net: tune to within ±15 cents of target and accept the result. Anything tighter chases noise. ## Tuning procedure (per drum) 1. Seat the head: hand-tighten all 6 rods until snug, then add 1/4 turn each in star pattern (1-4-2-5-3-6). 2. Cross-tap each rod position with a stick handle while listening for the tap-pitch around the rim. Equalize tap pitches across all 6 positions to within 3 cents — this is the "even seat" step. 3. Bring the head to ~3% above target Hz (use a drum dial or tuner with center-strike). 4. Let the head rest 10 minutes (mylar relaxes); re-check pitch. 5. Fine-tune down to target ±5 cents. ## Bearing edge - 45° inward chamfer on the top edge of each shell, machined on a lathe with a V-tool or filed by hand. - Width of contact patch with head: 1.5–2.0 mm. Wider = warmer / more sustain; narrower = brighter / shorter sustain. Default 1.5 mm. - Polish the chamfer to remove burrs; a burr that snags the head will detune the drum non-uniformly. ## Pentatonic scale rationale A2-C3-E3-G3-A3 is a minor pentatonic (A-C-D-E-G) with the D omitted, giving: - A → C: minor third (3 semitones) - C → E: major third (4 semitones) - E → G: minor third (3 semitones) - G → A: major second (2 semitones) The non-uniform interval set means **no two adjacent drums are the same interval apart** — useful for the player's spatial memory. The bottom three drums form an A-minor triad (A-C-E), the top three form a C-major triad (C-E-G... wait, the top is G-A so the top triad is actually E-G-A, which is a sus4 with no fifth — treat it as an ambient cluster). Alternative tunings to consider for v0.2: - **Whole-tone:** A2-B2-C#3-D#3-F3 — equal 2-semitone steps, dreamy non-tonal. - **Drone-and-melody:** A2-A3 octave on drums 1 and 5, with C3-D3-E3 melody in the middle three. - **Custom:** swap the predicted tensions in `modular-pedestal-drum-stack-starter.wl` to derive a fabricator-specified scale. ## Strike-zone notes - **Center strike** excites primarily f01 (the fundamental). Use for melodic pentatonic phrases. - **Off-center strike** (1/3 radius from center) excites f11 (first overtone) more strongly — gives a "splash" tone with no clear pitch. - **Rim strike** excites the shell ring mode (1600–4900 Hz depending on drum). Treat as a percussive accent, not a pitched note. ## Sustain Single-headed open-shell drums have shorter sustain than double-headed; expect ~0.6 s for drum-1 down to ~0.2 s for drum-5. Sheet-metal shells with chamfered edges shorten this further (~30%) vs wood shells of the same dimensions. This is intentional — the stack is a **melodic** instrument, not an ambient one. Long sustain would smear pentatonic phrases into mud.