LOS ANGELES - The producers of "The Voice" may want to consider replacing those revolving chairs with ejector seats.

It appears that the entertainment industry is responding to heightened competition among televised karaoke contests by hiring fading superstars who will use the highly rated series to boost their profiles, then slip out after a while to revel in their revamped fame.

It worked wonders for Jennifer Lopez and Steven Tyler, both of whom exited from "American Idol" after just two seasons to go on arena tours this summer. It will probably do likewise for Mariah Carey, who will reportedly make $18 million a season when America's top-rated show returns in January.

On its rival "The X Factor," Britney Spears and Demi Lovato are replacing Paula Abdul and Nicole Scherzinger as judges. Spears will tell you that she plans to stick with "The X Factor," which has its second-season premiere on Sept. 12. If you believe that, you're probably also convinced that Kim Kardashian and Kris Humphries were truly, madly, deeply in love.

Judging from her news conference with reporters this week at the TV Critics Association summer press tour, Spears seemed more interested in looking for flies on the wall than talking about the show.

Producers for both programs will tell you that it's important to keep making their programs "fresh."

"No one has any job security, really, anymore, including myself," said Simon Cowell, who was key in creating both "Idol" and "Factor." "You're at the hands of the audience who watch the shows. We've always made a point on these shows of changing the shows whenever we think it's necessary. And for certain reasons we thought, even though the girls [Abdul and Scherzinger] did a great job last year, that we just felt we needed a change."

Translation: Replace judges every couple of years so that fans can stare at new, shiny objects.

The scramble for viewers

Being an internationally known commodity wasn't a prerequisite when "Idol" kicked things off in 2002. Randy Jackson and Cowell were behind-the-scenes Svengalis and Paula Abdul hadn't scored big on the pop charts in years.

But the landscape has changed. With so many of these shows on the air, ratings have slipped, forcing producers to come up with new ways to retain viewers. "Idol," whose numbers had been falling since 2008, averaged 22 million viewers last season, down from 26 million in 2011.

Cowell had to take a bite of humble pie when the rookie year of "The X Factor" drew 12.5 million, a solid number, but far below what he had predicted. He quickly moved to sign bigger names. Mike Darnell, who runs Fox's reality department, partly blames the lower-than-expected ratings on a lack of dynamic personalities on stage, but he also admits the onslaught of similarly themed programs has made an impact.

Fox Entertainment President Kevin Reilly went so far as to say that his network, which leans heavily on the success of "Idol" and "X Factor," may finish second to CBS in key demographics this upcoming season, something that hasn't happened in eight years.

The desire to reach younger viewers helps explain why Lovato, a 19-year-old former Disney tween idol, will join Spears, 31, and Cowell on the "Factor" panel. "Demi is so close to the demographic that is currently the landscape for pop music," said producer L.A. Reid, the fourth judge. "She has great taste, and she really leads us. And, of course, Britney is the pop princess and has been for quite some time. Our two ladies here, they keep Simon and me on point."

But can these new -- and most likely, temporary -- faces help these shows snag the numbers "Idol" enjoyed five years ago? That's a high note not even Carey can reach.

njustin@startribune.com • 612-673-7431 • Twitter: @nealjustin