Buoyed by the success of its expanded slate of pop acts, the Mann Center for the Performing Arts is adding a second stage.

The Skyline Stage and Lawn, opening at the end of July with two concerts by ethereal Icelandic band Sigur Rós, perches on a newly annexed three or four acres of Fairmount Park leased to the Mann by the city. The patch of green, where listeners will stand, is larger than the current lawn; the stage is smaller and portable.

The changes are in response to an evolving relationship between musicians and fans, says Mann president and CEO Catherine M. Cahill.

"What we've discovered is that a number of artists and audiences don't want a 4,500-seat undercover venue. They want to stand, audiences want to be up close to the artists, and that's becoming more common in a lot of indie rock groups," she said.

The high, expansive new area, which increases the arts campus' size by almost a third and will undergo more refinements for next summer, brings visitors an impressive vista of downtown towers three miles to the southeast.

"The view is to die for," says Cahill.

Mann leaders are finalizing other changes expected to be complete for the summer of 2013. The current lawn will be enlarged by eliminating some terrace seating and bringing the grassy semicircle closer to the edge of the theater. The current, often lonely sea of 4,800 green plastic seats will be removed, replaced with 2,000 new seats.

This change has been talked about for well over a decade, since audiences tend to divide themselves between the covered (more expensive) seating, and the more casual (cheaper) lawn, popular with gourmand picnickers and young families introducing children to orchestral music.

Ultimately, those choosing the lawn will be rewarded with better sound and visuals than is currently the case. Three new video screens will be mounted on the angular shed, and an enhanced audio system is being designed.

Mann fund-raisers are well along in the campaign to pay for renovations. A $16 million drive already has brought in $12.5 million in cash and pledges. Primary sources are $3 million from the city, $2.5 million from the Commonwealth, $1.75 million from the William Penn Foundation, and, in the Mann's single largest gift from an individual, $2 million from H.F. "Gerry" Lenfest.

The new money will pay for physical changes and also give the Mann - which lives, financially speaking, hand-to-mouth - much-needed resources. Of the $16 million, $8.5 is for the building projects; $1 million will seed the beginning of an endowment; $1.2 million will go toward a cash reserve; and $1 million for a facilities reserve.

With artistic risk an endangered species in today's economy, the Mann will use $4 million to underwrite special initiatives - visiting and home orchestras, classical festivals, commissioning, co-productions with other summer festivals, and other projects - over six or seven years.

"Many people mistakenly believe we have a large endowment from the Mann family," said Cahill. Despite the center's maturity, it has no endowment. "Freddy Mann did amazing things when he was alive, however, endowment was not one of them." Of the Mann's $10 million a year operating budget, about 70 percent is earned, and 30 percent brought in through philanthropy.

Endowment, ticket sales, and donations are all ripe for growth. But how does the Mann measure success in attendance? Capacity for Verizon Hall downtown is 2,500. The Mann facility holds 13,500 - 3,900 in floor-level under-cover seating - which effectively means that even a classical event drawing double Verizon's fill seems to the eye like a so-so night. Cahill says if the lawn is covered, and floor level seating 75 percent sold, that's success.

The visual element of the Mann experience has become more urgent to meet a more visual generation on its own terms. Cameras will capture close-ups of instrumentalists. "We want to bring to life what's going on on stage," says Cahill.

The Mann opened in 1976 as the local summer home of the Philadelphia Orchestra, which, until a few decades ago, presented 18 concerts there. But audiences have dwindled. It's not clear whether some of the damage is self-inflicted. Some say eliminating the tradition of free lawn tickets has hurt, as has the lack of an artistic leader for orchestra concerts. Charles Dutoit, who made his Philadelphia Orchestra debut in 1980 at what was then called the Mann Music Center, took the helm in 1990, and resigned after nearly a decade.

Since then, the regular roll call of big-name soloists and conductors has all but disappeared. The orchestra now travels to Vail, Colo., in summer, does free neighborhood concerts, and has reduced its Mann concerts to six.

"There's been less classical, that's for sure, because the orchestra has cut its weeks back," said Cahill. "We've had a resurgence of pop music, and there's appetite for it." Asked whether the Mann would want to restore a heavier Philadelphia Orchestra presence to the center, Cahill said: "If we could have had an economic relationship with them that's feasible, absolutely yes." Regardless of the orchestra's commitment, Cahill says Mann seasons will include nine orchestral programs. This summer, the Pittsburgh Symphony Orchestra will do two concerts, the Chamber Orchestra of Philadelphia one.

The summer opened with the orchestra of the Curtis Institute of Music, whose student pianists and conductors have become important sources of talent for the Mann. But most orchestral concerts now are orchestral only in the broadest sense. One Pittsburgh appearance marks the important Mann debut of music director Manfred Honeck. But the other is built around a virtual (video game) personality: The Legend of Zelda. Fireworks, Broadway singers, a jazz trumpeter, movie music and a talent-show personality weave through the rest of the orchestral season. It's a far cry from the Dutoit's multiyear Mahler cycle.

The shift to popular personalities goes hand-in-hand with video screens and better audio. "It's considered standard in our industry," says Cahill. "We believe the lawn is the entryway for people new to classical experiences."

Another entryway is a strong podium personality - a personification to put on ticket brochures and billboards. But until the Mann and Philadelphia Orchestra have a long-term agreement, no one can be hired. Now there's the additional question of what kind of musical leader it would be. A classical conductor? An instrumentalist? One personality? Two?

Whoever it might be, the mandate would be to grow audiences, which is what the new second stage - meant for crowds of between 500 and 4,000 - is all about.

"We don't have an audience to do a Mahler cycle at the Mann," says Cahill. "Many of the people who come to the Mann don't cross the threshold of another venue during the year. We have to continue to draw new audiences."