# Celesta Design Study ## Design Thesis The celesta is a keyboard instrument, but the sound source is a set of struck steel bars over resonators. The design problem sits between piano action, glockenspiel-like bar behavior, resonator coupling, and damping. A serious packet must treat those interfaces as setup variables instead of pretending the keyboard alone defines the instrument. ## Mechanism Overview A key moves an action that throws a felt hammer toward a steel bar. The hammer must strike and rebound cleanly so it excites the bar without muting it. The bar is suspended at support points that preserve vibration while keeping the bar stable under repeated impact. Below the bar, a resonator box reinforces the sound. A damper controls sustain and release when the key is lifted. This L2 packet names the review surfaces and test gates, but it does not choose final bar geometry, pitch range, resonator volume, hammer mass, felt hardness, key count, or action ratio. Those values need measured or reviewed authority before any build-ready packet can advance. ## Subsystems ### Keyboard And Action - The keyboard should provide repeatable hammer motion without excessive noise or lost motion. - Candidate actions can borrow from piano-style principles, but the final linkage must be scaled to the bar, hammer, and damper behavior. - Key return, escapement or rebound behavior, hammer checking, and regulation are unresolved. - Action geometry is pending measurement and should not be copied from a drawing without review. - L2 evidence target: a small key-action mule that records key feel, hammer travel, rebound, checking, damper timing, regulation access, and noise. - Authority boundary: no key count, spacing, lever ratio, pivot position, or spring force is released. ### Felt Hammers - Hammer felt hardness, contact shape, rebound behavior, and wear are primary tone variables. - The hammer should excite the bar without staying in contact long enough to choke the sound. - Strike position is a future setup parameter, not a released location in this L2 packet. - A first prototype should compare hammer coverings and rebound behavior before scaling to a full keyboard. - L2 evidence target: hammer material and rebound comparison notes against a single trial bar. - Authority boundary: no hammer mass, felt hardness, strike point, or voicing target is released. ### Steel Bars - The steel bars are the primary sound generators. - Bar material, graduation, undercutting or profiling, suspension points, and tuning workflow require measurement. - Bar tuning is intentionally not specified here. - Future design work should separate raw bar blank preparation from final tuning and voicing. - L2 evidence target: a bar coupon log for sustain, decay, tuning response, support sensitivity, surface condition, and repeatable strike behavior. - Authority boundary: no bar length, width, thickness, profile, material grade, pitch, or undercutting geometry is released. ### Resonator Boxes - Each resonator must be matched to the bar behavior through measurement or reviewed acoustic modeling. - Box material, volume, opening, placement, and coupling are unresolved. - Resonators must be accessible enough for inspection and adjustment during prototype work. - No resonator dimensions or tuning values are claimed here. - L2 evidence target: a resonator comparison using the same bar coupon so loudness, color, sustain, and coupling can be observed before dimensions are chosen. - Authority boundary: no resonator volume, opening, wall thickness, or placement is released. ### Dampers - Dampers need enough control to stop notes cleanly without dulling attack. - Damper material, placement, lift timing, and key-release behavior are open. - The damper system must work with hammer rebound and bar sustain, not fight them. - Release noise should be treated as a validation item. - L2 evidence target: damper material and lift-timing notes from the action mule and bar coupon. - Authority boundary: no damper material, lift distance, timing, or geometry is released. ### Frame And Service Access - The frame must hold the keyboard, bars, resonators, dampers, and action in alignment while allowing regulation and tuning access. - Service access matters because bars, hammers, dampers, and resonators all need adjustment during prototype work. - Transport stability, dust protection, and cover design are future questions. - L2 evidence target: an interface map that separates bar support, hammer access, resonator clearance, damper regulation, and service cover removal. - Authority boundary: no case dimensions, frame stock, joinery, or fabrication release is provided. ## Parametric Intent Future work should name parameters before assigning values: - `estimate_key_count_pending_measurement` - `estimate_bar_count_pending_measurement` - `estimate_bar_material_pending_measurement` - `estimate_bar_support_point_pending_measurement` - `estimate_hammer_mass_pending_measurement` - `estimate_hammer_felt_hardness_pending_measurement` - `estimate_resonator_volume_pending_measurement` - `estimate_damper_lift_pending_measurement` - `estimate_action_ratio_pending_measurement` These names are placeholders only. They are not dimensions, tuning values, or performance targets. ## First Measurement Gates - Hammer test: verify clean strike and rebound against a single trial bar. - Bar test: measure sustain, decay, and tuning response before designing a full graduated set. - Suspension test: confirm that supports hold the bar without choking it. - Resonator test: compare bar sound with and without a trial resonator. - Damper test: verify clean stop without excessive release noise. - Action test: confirm repeatable key feel and hammer travel on a small mechanism before scaling. - Service test: confirm bars, hammers, dampers, and resonators are reachable for regulation. ## L2 Packet Gates | Gate | Current authority | Promotion evidence | | --- | --- | --- | | Bar coupon | pending_measurement | Measured sustain, decay, support sensitivity, tuning response, and strike repeatability. | | Hammer comparison | pending_measurement | Rebound and tone notes from alternate felt/contact materials against one trial bar. | | Action mule | pending_measurement | Key feel, hammer travel, checking, damper timing, and regulation access observations. | | Resonator comparison | pending_measurement | Side-by-side notes with no claimed tuned volumes or final dimensions. | | Damper release | pending_measurement | Clean stop and release-noise observations under repeatable key action. | | CAD/drawings | pending_measurement | Reviewed CAD, DXF, or drawing authority after measured parameters exist. | ## L2 Boundary This design study is a build-packet candidate. It names subsystems, coupon classes, and measurement gates, but it does not define a scale, tuning system, bar geometry, resonator geometry, action drawing, CAD model, DXF, or fabrication release.