LITITZ, Pa.—This town of 9,400 people in Amish country tells the story of the modern concert industry.

In 1968, when Frankie Valli and his group rolled in for a show, two young brothers who did sound for local dances turned the Four Seasons into one of the first music acts to tour with its own speaker system. The brothers built a reputation on the road, but they never moved out of Lititz. Their company became an anchor for a cluster of businesses that now supply the sound and spectacle for many of the world's biggest acts.

The effect that lets pop-star Katy Perry soar over her audience while clutching a bunch of balloons. The battalion of speakers blasting Paul McCartney's voice in stadiums designed for sports, not music. The sliding catwalk that takes a singing, dancing Justin Timberlake from the stage to the rear of an arena. All this gear, currently crisscrossing America in tractor-trailers, was engineered and built in Lititz, along with the apparatus for blockbuster tours of the past by U2, the Rolling Stones, Madonna and Michael Jackson. The place has an air of secrecy: Because entertainers want a surprise when the curtain goes up, much of the work here is done in secret by companies that don't put their names on their buildings.

Once wired with tinny speakers and harsh lights, the world of live entertainment is now powered by computer systems that control sophisticated video displays on sets worth tens of millions of dollars.

The technology has been accelerated by the Darwinian forces of the music business. Concert tours, once used primarily as a way to get fans to buy records, have become the backbone of the industry after those record sales collapsed. As performers rely more heavily on their road earnings, they are now forced to tour more frequently and amp up the fireworks. Purists may see this as garish smoke and mirrors, but when you're performing in venues with 50,000 seats and no roof, you've got to do something.