EchoFilm — An Integrated Evidence Chain: Sound × Dust × Human (Urban Rooms & Space Habitats)

Natural soundscapes span infrasound to ultrasound and co‑organize living systems. A cross‑disciplinary evidence chain now supports two complementary pathways by which organized sound modulates indoor human–microbiome outcomes. Host pathway: slow 2–8 Hz rhythmic scaffolds entrain respiration and the autonomic nervous system, yielding higher nightly HRV (RMSSD) and more stable sleep; via the cholinergic anti‑inflammatory reflex, improved vagal tone shifts gut barrier, motility, and immune tone, biasing gut‑microbiome niches (alpha‑diversity and SCFAs). Exposure pathway: audible acoustics—especially 1–3 kHz—drive acoustic agglomeration and near‑wall acoustic streaming; particle statistics (d50/CMD) increase, PM2.5 falls, and settling/filtration rise. Together with material‑layer chemistry/roughness (asphalt, concrete, glass, metals; VOC backgrounds), this rewires what reaches the breathing zone and alters the biological composition of inhaled air (pollen, fungal spores, bacteria vs mineral dust). Urban “spectrum disruptors” (broadband noise, heat‑island refraction, RF clutter) mask natural bands and dilute biophony; wildlife routing (e.g., bats, 20–110+ kHz) and façade materials further shape indoor exposure profiles. EchoFilm restores a safety‑capped, full‑spectrum window‑to‑nature indoors (audible bands plus an optional ecological ultrasound cue, never as a microbe‑level actuator) while logging air (APS/OPC size spectra, VOCs, 16S/ITS bioaerosols, polarization/depolarization typing) and human physiology (nightly HRV). We specify one proof‑of‑closure trial (Full vs ANC‑only vs Eco‑placebo; equal‑loudness) that demonstrates both pathways in the same homes. Primary endpoints couple HRV/sleep with airborne biological diversity (not just mass); a materials panel links boundary‑layer acoustics to near‑wall exposure. The framework unifies physics (agglomeration, boundary layers), biology (microbiome, biophony), and indoor environmental engineering (IAQ, optics) into one actionable, testable synthesis.