Survivors Roger Daltrey and John Entwistle.

While “Tommy” is more popular, especially since its Broadway revival earlier this decade, “Quadrophenia” “has a bit more depth than “Tommy” musically,” Simon Townshend says. “It has more real-life meaning, too.

I think the fantasy idea of ‘Tommy’ was appealing to people, but it has more of a commercial edge to it,” he says. “And things that are commercial suffer in some ways. They age quicker for a start.”

“Quadrophenia,” while it’s in part named after an audio format that long since died out (quadrophonic sound), seems to age well because it deals with men looking back at their youth — a theme that works as well now, as the Who grow into their 50s, as it did 24 years ago.

“‘Quadrophenia’ has got that gang thing as part of it,” Townshend adds, citing the old Brighton riots between the mods and the rockers. “And all kids want to be part of something when they’re growing up; they all want to feel involved with something.”

Plus, he says, “it has good music. And that won’t ever date. It will stand the test of time.”

Still, “Quadrophenia” is virtually unknown as a rock opera compared to “Tommy.”

“Songs like ‘5:15’ were popular,” Townshend says. “People know the singles. But I’m sure there must be some who come [to the concert] and are not familiar with it as an album. Maybe I’m wrong. It’s a difficult one to gauge with 15,000 to 20,000 people in an audience. You just wonder.

“But what I do know,” he goes on, “is that by the end of the set, when we’re playing ‘Love, Reign O’er Me,’ you get this incredible sense that all the audience knows the words to the song. You feel it, going from the people immediately in front of the stage right to the very back.”

How difficult is the piece to play?

“It has its moments,” Townshend says. “There are a few areas that are a bit complex — especially the links between pieces, the synthesized sections.”

Some of the songs have more than a couple of key changes as well, he says, and "Dr. Jimmy,” “switches key at least four or five times.”

It took a month of rehearsals before the band played excerpts from “Quadrophenia” in public, at a benefit for the Prince’s Trust concert in England last summer that featured sets by Eric Clapton, Bob Dylan and Alanis Morissette.

And rehearsals were marred when Gary Glitter nearly poked out Daltrey’s eye in a bit of stage business. By the time the show played six sold-out nights at Madison Square Garden, Daltrey had to wear an eyepatch.

Earlier, Townshend had accompanied Daltrey on his own solo tour, as did some of the other featured members of the current tour, including drummer Zak Starkey, the son of Beatles drummer Ringo, who has really blossomed in his role sitting in for the late Keith Moon.

Reports of brother Pete’s hearing problems are greatly exaggerated, his little brother says.

“I think there’s a misunderstanding there,” he says. “Pete plays about half the show on electric.”

But the Who leader also spends a lot of time on the acoustic guitar, playing rhythms as his little brother takes the guitar leads. “I think he enjoys playing acoustic guitar,” Simon Townshend says.

He also says the elder Townshend takes too many liberties with the music line. “He tends to improvise very much,” Simon says. “The main hooks of the music are done on guitar, and he has a tendency to improvise them whereas the audience would rather hear the raw material.

“When I was doing them, he enjoyed hearing me play them in basic form.”

The Townshend brothers share lead parts.

“He takes a few solos, and I take a few,” Simon says. But at the end of the show, when it’s time to run through a few Who oldies, it’s Pete Townshend who takes over on such nuggets as “Substitute” and “Can’t Explain.”

Simon Townshend always looked up to his big brother.

“I was two years old when Pete left home,” he says. “I’m 36 now, 16 years younger than Pete. He left home, and almost immediately started to become very successful when I was young.”

That inspired the younger brother to play guitar. He’s turned out such solo albums as “Moving Target” and “Sweet Sound” and has contributed to solo works by Daltrey and Townshend, as well as albums by the Pretenders, Mick Ronson and Duran Duran, among others.

But being a brother to a rock legend brings a persistent shadow as well.

“It’s just one of those things. You’re in the position you’re in from birth,” he says.

By the same token, having the same musical genes, Simon Townshend says, “I feel like royalty.”

It’s a talent he passed on to his 19-year-old son, who is drummer for his Simon Townshend Band, whose album “Among Us” is due out on Sept. 2.

It shouldn’t be too surprising,

Townshend says of the line of musicians in the family. “I really think that if you’re born into a family of golfers, you’ll probably hit the ball better than those who are not.”