Last year, Perry's stage -- one of the festival's eight stages, focusing largely on DJs and electronic music, and named for Lollapalooza founder Perry Farrell -- expanded to an enormous circus tent with a 15,000-person capacity.

As it proved to be one of the most popular attractions at the weekend concert series, the tent roof trapped too much heat from the mass of dancers. By the second day of Lollapalooza 2011, portions of the big top had been stripped away to allow heat and humidity to escape.

This year, Perry's stage will be open-air like the others and will feature a theatrical set design courtesy of one of the acts, Swedish DJ Avicii.

Secondly, promoters are trying a new tactic to battle the perennial horde of fence-jumpers.

The last two years at Lollapalooza have seen a marked increase in the number of young fans assaulting the festival's perimeter fence in order to get in without paying. Sometimes it's one or two individuals -- including several who were critically injured in their attempts last year -- but last year saw flash mobs of up to a hundred at a time overwhelming certain sections of fence, occasionally employing boards as ramps.

Organizers at C3 Presents, producers of Lollapalooza, tell the Sun-Times this year's perimeter will include "The Black Fence," an 8-foot anti-scale barricade used in Washington, D.C., around government buildings and during citizen protests.

"The more pressure you put on it, the sturdier it gets," said Charlie Jones, a partner in C3.

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