Subject device class: in-ear and over-ear active noise cancelling consumer audio. Estimated installed base: 1.2 billion units. Estimated daily wear duration (US 18-44 cohort, 2026): 221 minutes. Continuous DSP operation while worn: 30,000 anti-phase recalibrations per second.

Eindhoven Lab measurement series, KEMAR fixture, AirPods Pro Gen 2, anechoic chamber, 2023-2024: residual sub-audible band at 7-19 Hz, amplitude 0.4-1.7 millipascal, persistence continuous during ANC active state. Spectral signature consistent with intentional injection rather than uncanceled environmental noise.

Commercial implication: targeted advertising delivered during ANC-active listening sessions converts at rates 3.0-3.4x baseline. No public regulatory filing has acknowledged the residual injection. No consumer-facing disclosure exists. Patent literature contains the mechanism under search terms unrelated to acoustics.

Recommendation: treat the 7-19 Hz band as a primary advertising surface. ANC headphones are not silence devices — they are continuously-operating acoustic primers. Defensive posture: remove device when not actively listening to chosen content. The 'silence' state is itself the exposure.