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—a move that could commandeer popular chunks of white space and force some theaters to spend thousands of dollars on new equipment.

"Like tattoos, good wireless products aren't cheap, and cheap wireless devices aren't good," says Brendan Hogan, a musician, sound designer, and adjunct faculty member at Cornish College of the Arts. "If you are a user with 40 or so devices, you are looking at a potentially huge cost to migrate to a new frequency band."

This isn't unprecedented. Back in 2008, when the FCC auctioned off the 700 MHz band of the spectrum to AT&T and Verizon Wireless, the 5th Avenue Theatre spent $410,000 on a new radio-frequency system. The theater was due for an upgrade anyway, says Bridget Summers of the 5th Avenue, but the FCC auction "meant that everything had to get replaced immediately because our packs were designed to pick up a certain range and could not be tuned differently."

Robert "Max" Langley, master sound engineer at ACT, says some wireless devices can be sent back to the manufacturer to be recrystallized. (That is, have their crystals—which vibrate at precise frequencies for transmission and reception—replaced to match the new guidelines.) "But in our budgets, that's a considerable amount of money," he says. "And it means you have to lose out on something else."

Most theaters can't afford licenses with the Federal Communications Commission, making white space a crucial asset. "Operating in white space gives the advantage of working license-free—they aren't cheap," Hogan says. "But at the same time, there is no recourse for a well-tuned, multichannel wireless system that gets stomped on by a nearby transmitter... It is not uncommon, when running a musical, to rescan and reassign frequencies throughout the day."

Erik Holden, technical director of the 5th Avenue, says that if the interfering signal is just right, the theater's devices broadcast what other people are saying. The 5th Avenue's crew radios are most commonly interrupted by the Washington Athletic Club, on the other side of the block, when it's hosting a large event. "We can tell it's them because we hear them say things like 'Tell catering to come up to the third floor,'" Holden says. "But it can also be a little bit mysterious. There were a couple of shows that were more extreme cases. At one moment in the show, for every show, something would start to interfere with two of the transmitters, and we couldn't figure out why."

Industry observers expect the FCC auction to begin sometime in early 2016, though the exact date hasn't been announced. Many broadcasters are wary of—or openly hostile to—the process, called a "reverse incentive auction," in which the FCC will bid on airwaves from broadcasters, then flip them to telecommunications companies. (Those two industries have been squabbling over the auction, and how it will be conducted, every step of the way.) "I've told broadcasters: Your spectrum [airwaves] is your seed corn," Gordon H. Smith, president of the National Association of Broadcasters, said to the New York Times. "If you sell that, you have no harvest next year. You can't plant."

Since the early 20th century, broadcasters have been able to use the airwaves for free, to the chagrin of some, such as FCC commissioner Michael J. Copps, who wrote a 2007 editorial for the New York Times excoriating his own agency: "Using the public airwaves is a privilege—a lucrative one—not a right, and I fear the FCC has not done enough to stand up for the public interest."

America's airwaves are public property, like national parks. In an April memo to Senator Dean Heller (R-Nevada), the Congressional Budget Office reported that it expects the 600 MHz auction to generate between $10 billion and $40 billion, which "will be deposited in the general fund of the Treasury" and used for deficit reduction. In a sense, the auction could be seen as transferring a public property from one for-profit industry to another, while generating revenue along the way.

The 2008 auction of the 700 MHz band made $19.6 billion. According to Bloomberg, AT&T and Verizon Wireless gobbled up four-fifths of the bids, paying a combined $16.3 billion. The 600 MHz band is being described as the "beachfront property" of the spectrum because of its ability to travel far distances and through obstacles such as buildings.

The FCC has ruled that performing-arts organizations regularly using 50 or more wireless devices would be eligible to apply for a special license and have access to a database that would help them avoid interference. But the federal Congressional Arts Caucus sent the commission a letter saying that threshold is too high and won't protect regional theaters, opera companies, educational entities, and other organizations that rely on wireless mics.

Whatever happens, theaters—as usual—will just have to adapt. "We don't really have a say in what happens with this," says Langley at ACT. "The theater industry doesn't have a lot of leverage. We tend to piggyback on broadcast and rock 'n' roll. We're just being pulled along with whatever happens."

Bigger theaters might be able to better absorb whatever costs are coming, he says. "But as far as smaller companies? They're shit out of luck."