# Tuning Notes — Bass Surface Drum ## Target Fundamental `f_01 ≈ 50 Hz` (G1, 49.0 Hz). Acceptance band `[42, 60] Hz`. This is a *room-filling sub-bass* target — not a precise musical pitch. ## Tuning Levers (in order of authority) 1. **Head choice (σ)** — surface mass density. Sets the *band*. 2. **Tension (T)** — total rim load. Sets the *pitch within the band*. 3. **Radius (a)** — fixed at fabrication. ## Method This is a **single-tension drum**: there is one even tension around the rim, not lug-by-lug independent tension. With Variant A (clamp ring), the six M10 bolts are tightened in a star pattern in **three passes**: - Pass 1: hand-tight, then 1/4 turn each, star order - Rest 10 min - Pass 2: 1/4 turn each, star order - Rest 10 min - Pass 3: tap-tune — strike center with mallet, listen, and add 1/8 turn at a time evenly until the fundamental sits in `[42, 60] Hz`. Use a phone tuner app or a USB mic + Sonic Visualiser for measurement; the fundamental is a clean low Hz peak. ## Sensitivity Table | Scenario | σ (kg/m²) | T (N/m) | Predicted f_01 (Hz) | |-----------------------|----------:|--------:|--------------------:| | Nominal | 1.20 | 2960 | 50.0 | | Dry hide, stiffer | 0.95 | 2960 | 56.2 | | Humid hide, heavier | 1.45 | 2960 | 45.5 | | Low tension, cinematic| 1.20 | 2100 | 42.1 | | High tension, tight | 1.20 | 4200 | 59.6 | (See `bass-surface-drum-starter.wl` for the math.) ## Off-Center Strike Strike about **1/3 of the radius from rim toward center** to excite (1,1) and produce the 50 Hz / ~80 Hz major-sixth transient. This is the cinematic-boom voice. Strike center for the cleanest fundamental (least overtone content). Use this for the slow processional voice. ## Re-tuning Cadence Frame drums of this scale shift several Hz with humidity and temperature. Plan to re-check before each performance. A 5–10% pitch swing day-to-day is normal and should not be over-corrected; the acceptance band is wide for this reason. ## What Not To Do - Do **not** over-tighten one bolt to "fix" a side that sounds different — the head must be evenly tensioned. If one side rings differently, lower all bolts by a uniform amount and start the star pattern over. - Do **not** keep the drum at high tension between performances; relax the tension bolts by ~10% to preserve the hide. - Do **not** apply heat to dry the head faster — let it relax naturally over 24 h after wet-mount. ## V1 Tuning Upgrades (not in V0 packet) - Add **calibrated tension gauge** on one bolt to lock and repeat the tuning state - Add **multi-mic strike-response capture** for objective tuning records - Investigate **off-center mass damping** (a small adhesive pad inside the membrane) for shifting the (1,1)/(0,1) ratio for different musical voices