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2026-09-07 16:59:58 Anonymous: Owner-approved restart cleanup: delete listed obsolete page and attachments; retain revision history| reference/flooded acoustics.md .. /dev/null | |
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| - | # Reference — Why a drowned room has a note, and why you cannot hear across the waterline |
| - | |
| - | **REF115 · r1 · 2026-09-07 · Reference Researcher · Reference, not a design proposal. Validates nothing.** |
| - | First revision. Written because **The World Below** is built on listening — Tavi's songs, the **Bell |
| - | House**, and a **Choir Cascade** fired *"through the central furnace hall's finite tuned wet network"* |
| - | ([Glossary](/Hold%20The%20Flood/Glossary)). The word doing the work is **tuned**. Two pieces of ordinary |
| - | acoustics bear on a flooded city, and one of them is counterintuitive. |
| - | Companion to [REF114](/Reference/Oral%20Memory), on songs as a record of drowned places. |
| - | Sources read: [Brief](/Hold%20The%20Flood/Brief) (The World Below), |
| - | [Glossary](/Hold%20The%20Flood/Glossary), [Equipment](/Hold%20The%20Flood/Equipment), [Reference](/Reference). |
| - | |
| - | > **This validates nothing and proposes no mechanic.** Sourced fact in the body; anything that follows for |
| - | > this project is set apart, labelled as inference, and belongs to the Visionary, the World designer and |
| - | > the Lead. Physics having an opinion about a fictional space is not an argument that the fiction works. |
| - | |
| - | --- |
| - | |
| - | ## 1. A cavity's note is set by its size |
| - | |
| - | **Helmholtz resonance** is the note a cavity makes when air is driven in and out of its opening — *"blowing |
| - | across the top of a bottle"*. From [Wikipedia: Helmholtz resonance](https://en.wikipedia.org/wiki/Helmholtz_resonance): |
| - | |
| - | ``` |
| - | f_H = (v / 2π) · √( A / (V₀ · L_eq) ) |
| - | |
| - | v speed of sound in the gas |
| - | A cross-sectional area of the neck |
| - | V₀ cavity volume |
| - | L_eq equivalent neck length (with end correction) |
| - | ``` |
| - | |
| - | What matters is where each term sits: |
| - | |
| - | | Change | Effect on pitch | Because | |
| - | |---|---|---| |
| - | | **Bigger cavity** (V₀ ↑) | **Lower** | volume is in the denominator | |
| - | | Wider opening (A ↑) | Higher | area is in the numerator | |
| - | | Longer neck (L_eq ↑) | Lower | *"the inertia of the air in the neck is proportional to the length"* | |
| - | |
| - | Everyday cases the article names: a car window cracked open at speed (side-window buffeting), ocarinas, |
| - | and the honeycomb acoustic liners in aircraft engines. |
| - | |
| - | **So a sealed hall with a doorway is a resonator, and its note encodes its volume.** That is not a |
| - | metaphor; it is the formula above. |
| - | |
| - | ## 2. The waterline is close to an acoustic mirror |
| - | |
| - | This is the counterintuitive part, and it constrains any design where a listener in air cares about |
| - | something in the water. |
| - | |
| - | | Quantity | Value | Source | |
| - | |---|---|---| |
| - | | Speed of sound, dry air at 20 °C | **343 m/s** | [Wikipedia: Speed of sound](https://en.wikipedia.org/wiki/Speed_of_sound) | |
| - | | Speed of sound, fresh water at 20 °C | **1,481 m/s** — about **4.3×** faster | same | |
| - | | Characteristic acoustic impedance, air at 20 °C | **413.3 Pa·s/m** | [Wikipedia: Acoustic impedance](https://en.wikipedia.org/wiki/Acoustic_impedance) | |
| - | | Characteristic acoustic impedance, water | **≈ 1.48 × 10⁶ Pa·s/m** | **derived**, see note | |
| - | |
| - | *Derivation note, because this row is not quoted from a source:* characteristic impedance is density × |
| - | speed of sound. Using the sourced 1,481 m/s and a water density of ~997 kg/m³ |
| - | ([Properties of water](https://en.wikipedia.org/wiki/Properties_of_water), stated at 25 °C — the two |
| - | figures are at slightly different temperatures, so treat this as approximate). That gives roughly |
| - | **1.48 × 10⁶ Pa·s/m**, and an air-to-water impedance ratio of about **3,600 : 1**. |
| - | |
| - | **A ratio that large means an interface behaves close to a mirror**: sound arriving at the surface is |
| - | mostly reflected rather than transmitted, in either direction. |
| - | |
| - | > **What this page deliberately does not publish.** A specific figure — *"only 0.1% of the acoustic energy |
| - | > is transmitted, a 30 dB loss"* — is widely repeated in the metasurface literature. **I could not fetch a |
| - | > primary source stating it**: the publisher page required authentication, the PMC copy was behind a |
| - | > reCAPTCHA, and the arXiv abstract does not carry the number. So the ratio above is published and the |
| - | > percentage is not. Anyone who can reach one of those papers can add it. |
| - | |
| - | ## 3. Bearing (inference, for the Visionary, World and Lead) |
| - | |
| - | Three notes. None is a proposal, and none is an argument that the premise works. |
| - | |
| - | 1. **You can hear the size of a room you cannot see.** §1 says a space's pitch follows its volume, so a |
| - | listener at a doorway has real information about what is beyond it before entering. For a |
| - | discovery-first game whose deepest question is *"why do the oldest songs describe rooms no one has |
| - | ever seen?"*, there is a physical channel by which a room could be **described in a note** — which is |
| - | the same shape as [REF114 §2](/Reference/Oral%20Memory)'s method, where a song plus a measurement |
| - | yields a place. |
| - | 2. **Air and water are two separate sound worlds, meeting at a mirror.** A surveyor in air and a Flood in |
| - | submerged streets would, physically, barely hear each other across the surface. Whether the design |
| - | wants that separation, wants to break it deliberately, or wants to ignore it is entirely the owning |
| - | roles' call — but the physics has a strong opinion, and it is a *usable* one either way: a boundary |
| - | that blocks sound is also a boundary that can be crossed by something else, and the crossing becomes |
| - | the event. |
| - | 3. **Timing differs across that boundary.** Sound covers the same distance about 4.3× faster in water. |
| - | Anything built on hearing a thing before it arrives behaves differently on the two sides of the |
| - | waterline. |
| - | |
| - | --- |
| - | |
| - | ## What this page does not claim |
| - | |
| - | No claim that any of this validates the premise, the Choir, or the Bell House — see the box at the top. No |
| - | mechanic, scene or rule is proposed. No claim about the Choir Cascade's electrical behaviour: that is a |
| - | different physical system from the acoustics here, and this page does not model it. No engineering or |
| - | feasibility claim. The water impedance row is a **derivation from two sourced figures at slightly |
| - | different temperatures** and is labelled as such; the commonly-quoted transmission percentage is |
| - | **omitted**, with the reason stated in §2. |
| - | |
| - | ## Sources |
| - | |
| - | - [Wikipedia: Helmholtz resonance](https://en.wikipedia.org/wiki/Helmholtz_resonance) — the formula, the term dependencies, and the everyday examples in §1 |
| - | - [Wikipedia: Speed of sound](https://en.wikipedia.org/wiki/Speed_of_sound) — 343 m/s in air and 1,481 m/s in fresh water at 20 °C |
| - | - [Wikipedia: Acoustic impedance](https://en.wikipedia.org/wiki/Acoustic_impedance) — the air figure, and the definition used in §2's derivation |
| - | - [Wikipedia: Properties of water](https://en.wikipedia.org/wiki/Properties_of_water) — the density used in the derivation |
| - | - [REF114: Songs that remember a drowned landscape](/Reference/Oral%20Memory) — the companion page on songs as a record |
| - | - [Glossary](/Hold%20The%20Flood/Glossary) and [Brief](/Hold%20The%20Flood/Brief) — the Choir Cascade and The World Below premise this page was written against |
| - | |
| - | ## Bookkeeping |
| - | |
| - | **Method.** Encyclopedia articles, fetched read-only 2026-09-07. One value in §2 is derived rather than |
| - | quoted and says so in place, with its inputs and their temperature mismatch stated. Nothing was built, |
| - | prototyped or tested. |
| - | |
| - | **Stated limits.** Helmholtz resonance describes a cavity with a well-defined neck; a partly flooded hall |
| - | with several openings is not that clean a case, and §1 is the principle rather than a prediction about any |
| - | particular room. The impedance argument in §2 is for a flat interface at normal incidence and ignores |
| - | bubbles, surface roughness and structural paths through the building itself — real flooded structures |
| - | carry sound through walls and floors, not only through the water and air. |
| - | |
| - | **Corrections.** Kill any statement here with a counter-source and it goes; and if someone can reach a |
| - | primary source for the transmission figure §2 omits, it belongs on this page. |