--- instrument: tuned_slit_drum_bank family: idiophone acoustic_class: tuned_sheet_metal_tongues scale: chromatic_C3_B3 authority: private_review_blueprint --- # Design ## Summary The Tuned Slit Drum Bank is a 12-note chromatic idiophone. Each note is a small welded cold-rolled steel box with a U-shaped tongue cut into its top plate. The boxes mount in a shallow rack in chromatic order, played with soft mallets like a compact marimba. ## Lineage This Round 4 idiophone pulls from the R1 handpan/tongue-field craft and the R2 mute-tuned horn idea: small geometry changes become tuning changes. QMD also surfaced a tongue-drum SolidWorks skeletal-modeling tutorial and rectangular tongue-drum wiki/source stream, so this packet uses a skeletal master-layout approach and keeps tuning authority measurement-gated. ## Acoustic Model Each primary tongue is approximated as a rectangular cantilever beam: `f = beta1^2 / (2 pi L^2) * sqrt(E I / (rho A))` For a rectangular tongue, `I = w t^3 / 12` and `A = w t`, so width mostly affects loudness/stiffness margin and root behavior while length and thickness dominate the first estimate. ## Note Plan | Box | Note | Frequency Hz | Primary Role | Secondary Tongue | | ---: | --- | ---: | --- | --- | | 1 | C3 | 130.81 | validated pitch | G3 color | | 2 | C#3 | 138.59 | validated pitch | G#3 color | | 3 | D3 | 146.83 | validated pitch | A3 color | | 4 | D#3 | 155.56 | validated pitch | A#3 color | | 5 | E3 | 164.81 | validated pitch | B3 color | | 6 | F3 | 174.61 | validated pitch | C4 color | | 7 | F#3 | 185.00 | validated pitch | C#4 color | | 8 | G3 | 196.00 | validated pitch | D4 color | | 9 | G#3 | 207.65 | validated pitch | D#4 color | | 10 | A3 | 220.00 | validated pitch | E4 color | | 11 | A#3 | 233.08 | validated pitch | F4 color | | 12 | B3 | 246.94 | validated pitch | F#4 color | The secondary tongues are lower-amplitude color features. If they cross-talk or destabilize tuning, omit them from the first prototype. ## Geometry - Box outside envelope: 200 x 100 x 80 mm. - Top material: 1.5 mm cold-rolled steel. - Primary tongue width: 18 mm. - Primary tongue estimated length range: about 70-100 mm. - Root radius: 2.5 mm minimum after cutting. - Side seams: TIG welded after brake forming from a single blank. - Rack spacing: 12 mm gap between boxes, 8 degree player tilt. ## Tuning Coarse tune by lengthening/shortening the tongue tip cut. Fine tune by removing small mass near the tongue tip to raise pitch, or adding small removable mass to lower pitch during tests. Do not grind near the root unless resetting the whole box; root stiffness changes are hard to control. ## Readiness This is a private-review blueprint. The first build must start with tongue-root coupons and three prototype boxes (C3, F#3, B3) before cutting all twelve.