Clara Vance felt the frequency drop through the heavy Bakelite earcups of her Grand Halcyon PBX Switchboard Headphones. It hit her eardrums before it finished crossing the room air.
It didn’t begin as sound. It began as a cold barometric pressure against her eardrums. It had the unmistakable feel of an inductive magnetic loop trying to phase-lock with her inner ear.
At Station 6 (Intercom & Acoustic Relay), bolted to the rear junction of the checkout counter beside the cigarette rack, the sixty-hertz pilot lamp on the Bogen PA Amplifier flickered. On the circular green cathode-ray screen of her 89.9 FM crystal oscilloscope, the smooth sinusoidal wave buckled. It plunged twelve full cycles per second into a heavy, serrated 48.0 Hz sub-harmonic.
Clara pressed both palms against the black rubber cushions of her headset to seal out the room echo.
Directly above Aisle 2, the four eight-foot Phillips T8 fluorescent tubes flickered in violent, watery violet pulses. The aluminum T-bar grid supporting the drop-ceiling groaned under a sudden downward load. From the rectangular perimeter seams of Ceiling Tile #2B, a silent snowfall of yellow fiberglass dust and shredded black 10-mil laminate sifted downward.
Yet not a single speck of dust touched the beige linoleum below.
