VIOLIN, piano, flute, cello, harp -- the stars of the orchestra, sexy and ethereal, are known for their virtuosic solo flights. The timpani? Not so much.

These sizable, low-register kettledrums are usually the support players in the back, heard to be sure, but not much seen.

So why will 14 of the copper-bellied big boys receive top billing at the Pasadena Symphony's concert Saturday in the Pasadena Civic Auditorium?

Because Philip Glass' "Concerto Fantasy for Two Timpanists and Orchestra" is back in town, and so is Jonathan Haas -- the world's foremost solo timpanist and a passionate flag-bearer for the timpani's solo potential -- who commissioned the piece.

Joined by John Evans, principal timpanist for Florida's Naples Philharmonic Orchestra, Haas will play his 41st performance of this unprecedented work for multiple timpani, helping launch the Pasadena ensemble's 80th anniversary season.

Music director Jorge Mester, who gave the concerto its West Coast premiere in 2001 and has conducted many of its outings, isn't surprised at its success.

"First of all, it's by a great composer," he says, and second, the spectacle of two musicians manning seven timpani each "is a blast. And they're not banging away, they're playing part of the melodic fabric of the piece. It's an incredibly exciting thing."

According to Haas, a curiosity factor figures into the mix too. People are actually seeing the instrument that they're accustomed to just hearing play tonic and dominant passages.

"And here it is playing passages along with oboes, flutes, trumpets and strings," Haas says. "It's actually doing what the instrument does best, playing melody."

"I think at first the audience is just taken aback by how much copper is on the front of the stage," Evans cracks.

The visual effect of the repertoire's first double-timpani concerto has struck many critics.

The "two skilled drummers appear both as a powerful force outside of the orchestra (which almost ritualistically carries on the familiar Glassian formulas) yet still part of it," wrote Times music critic Mark Swed in 2001.

The concerto "is spectacular even before a note has been played," critic Robert Maycock observes in his book "Glass: A Portrait." Once it begins, "the spectacle becomes a matter for the ear as much as the eye. . . . As it builds up its momentum it takes on a gleeful quality, a peculiar mix of wit and weight, that turns the finale into a massive, exhilarating fun piece with slightly ghoulish undertones."

Glass used "all of the gifts that he has to make a very tightly constructed piece in its Minimalist fashion and one that has enormous, enormous audience appeal," says Los Angeles Opera music director James Conlon, who conducted Haas, timpanist Svetoslav Stoyanov and the Chicago Symphony Orchestra in the concerto at the Ravinia Festival outside Chicago in 2005.

With the timpani up front, his ears were pounding, Conlon says. "But it's very exciting." ("We spend most of our careers being told to play softer," Haas says with relish.)

Haas -- director of New York University's percussion studies, chair of the Juilliard pre-college percussion department and a longtime faculty artist at the Aspen (Colo.) Music Festival and School -- has made it the mission of his professional life to raise awareness of the melodic range and sonorous subtleties of his instrument of choice.

As a young student, he started out on the piano but preferred rock 'n' roll's pounding bass and the sound of the timpani, the lowest frequency in the orchestra. "I love low frequencies," he says, his energy and buoyant humor evident throughout a phone interview from his NYU studio.

"I like the way they feel, the way they sound, the way they travel through a concert hall. People can feel it in their feet, and they can feel it moving the air -- and it's just my thing. Obviously piccolo would not have been the right choice for me."

His "crazy idea" to move the timpani out in front of the orchestra, bolstered by support from his teacher at Juilliard, renowned New York Philharmonic timpanist Saul Goodman, received a significant boost in 1980 when Haas made his groundbreaking debut at Carnegie Recital Hall as a solo timpanist, "and the darn thing worked out."

A wide-ranging repertoireDUBBED the "Paganini of the timpani" by Ovation Magazine, Haas, 53, plays with major orchestras and has performed and/or recorded with the likes of Emerson, Lake & Palmer; Frank Zappa; Black Sabbath; his own jazz band, Johnny H. and the Prisoners of Swing; and his rock band, Clozshave.

He also runs Gemini Music Productions, a musician contracting company, and Kettles & Co., a rather handy percussion rental outfit.

Haas has also added to the orchestral timpani repertoire by commissioning more than 25 works. When he decided that a blowout showpiece was needed, on his short list of preferred composers were Zappa and the Minimalist Glass. After Zappa's death in 1993, Haas approached Glass, got the nod and scraped together the funding over several years while the prolific composer finished other commitments.

"I put off the timpani concerto for about 10 years because I just couldn't imagine how I would do it," Glass says in Maycock's book. But Haas' persistence finally won out, he recalls.

With the collaborative efforts of Haas and percussionist Ian Finkel, Glass' piece, in a three-movement-and-cadenza concerto format, received its world premiere in 2000, with Stoyanov and New York's American Symphony under Leon Botstein.

Its physically demanding nature hasn't discouraged other timpanists from tackling what Haas calls his Mt. Everest.

The timpani, with a range of about two octaves' worth of notes, requires the use of a variety of hard and soft mallets and must be tuned throughout a piece with a foot pedal mechanism. As the Glass piece "builds to a tremendous race to the finish at the end," Mester says, it's an aerobic tour de force.

"The biggest challenge was in figuring out where to place all the notes that are on the page," Evans says, "since it is written for so many drums." Then comes the task of choreographing arms, hands and feet to accommodate the fast and furious action -- sticks flying, feet pedaling -- spread over seven timpani.

"It's like taking a cha-cha dance class," Haas says, laughing. "We are continually tuning and retuning throughout the whole piece using the pedals. It's very balletic, very athletic, and it's really fun to play."

The secret is to not take it too seriously, Mester says. "Not every piece is German introspective, deep. This is a fun piece."

Evans agrees, but the initial rehearsals were punishing, he notes. "It took me a couple of months just to get where I could stretch my body to where it needed to be to play it without being sore."

Haas' foray into jazz led to a timpani-centric album of standards that includes a rediscovery of Duke Ellington's "Tympaturbably Blue." An orchestral arrangement of another track from the album, "Big Noise From Winnetka," is becoming one of Haas' encore concert pieces.

"I've tried to explore some of the most extreme boundaries," he says of his fascination with the big drums. To that end, he built the world's largest timpani, more than 6 feet in diameter -- out of a bowl used at the turn of the last century for cheese-making.

Ranch owners in Aspen had found three of the giant bowls buried on their land and tried to sell them as hot tubs, Haas says. He bought all three. His first monster drum made its official debut in 2003 at the Percussive Arts Society's annual convention. Its sound isn't loud, "it's just very, very low," he says.

Haas will finish the other two -- eventually. He dreams of one day having composer Tan Dun ("Crouching Tiger, Hidden Dragon") write a concerto for them. "But transportation is going to be very difficult, so I'm going slow on this particular project."

Other big ideasMEANWHILE, Haas has other projects on various burners. What he hopes will be a Broadway show of Zappa's music is in preliminary development. He has his next timpani concerto concept worked out and a composer in mind, although he's not ready to announce who that is, and his NYU Percussion Ensemble is collaborating with New York's Blessed Unrest theater company on an "off-off-Broadway percussion show" called "CoMotion," scheduled to run Feb. 29 to March 2.

Seemingly tireless, Haas doesn't confine his ideas to music. A father of three high school and college-age daughters, he has seen his share of teen "gross-out" movies. He decided he could do better. So, he says, swearing that he's not pulling anyone's leg, he's just finishing a screenplay, "Barf Bag," with every intention of seeing it become a feature film.

His inspiration: a concert at Carnegie Hall that he did when James Galway was on the bill. Before the renowned flutist went on in the second half, Haas says, "a pizza delivery guy delivered a huge pizza to Galway in his dressing room. I turned to the trumpet player and said, 'Wouldn't it be funny if, let's say, it was a bad pizza, and he was playing the flute. . . .?' "

Haas, ever optimistic, hopes they can afford Galway for the film.