Quorum · Probe 01

Can cheap Android phones hear 19 kHz across a classroom? One day to find out.

Microphone unavailable. Listening needs a secure context. Serve this file over https:// (Cloudflare Pages, or npx serve + a tunnel) and open that URL on the phone. Emitting still works from file://.

Sweep

— Hz
idle

Hold one tone

Use this while walking the room, so the listener can watch live SNR against distance, walls, and bodies.

Hearing floor: plenty of 18-year-olds hear 17–18 kHz clearly. Anything a student can hear is unusable in a lecture hall, so treat 19 kHz and up as the real product band — the sweep goes lower only to map the hardware.

Capture

Open the mic, hold still for the 2-second noise-floor reading, then start the sweep on the other phone.

Spectrum · 14–24 kHz · peak hold

— dB

Response by frequency

control tone not heard yet
HzPeakSNR 
no data yet

≥15 dB solid · 6–15 dB marginal, needs coding gain · <6 dB unusable on this hardware.

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