If (when) the FCC auctions off a portion of the 600 MHz broadcasting band, theaters will be forced to replace their wireless mic systems, making battery packs like this one obsolete.

If (when) the FCC auctions off a portion of the 600 MHz broadcasting band, theaters will be forced to replace their wireless mic systems, making battery packs like this one obsolete. MARK KITAOKA

For theaters around the country, the airwaves are already crowded. Finding open frequencies for their wireless microphones and other devices can be tricky. That requires hopping around in the unused “white space” of America’s broadcasting spectrum and hoping a more powerful transmission—from a passing emergency vehicle or big convention—doesn’t stomp on their signals, causing loud popping and squelching sounds.

But the airwaves are about to get even more packed.

Sound engineers and technical directors are warily watching for a new ruling from the Federal Communications Commission about when it will begin to auction off slivers of the 600 MHz band of the broadcasting spectrum…

Brend an Kiley has worked as a child actor in New Orleans, as a member of the junior press corps at the 1988 Republican National Convention, and, for one happy April, as a bootlegger’s assistant in Nicaragua....