(Updates audience figures in headline, first paragraph; adds The Voice ratings)
LOS ANGELES, May 22 (Reuters) - The finale of Fox's singing competition show "American Idol" drew the lowest viewership in its 13-year history, with 10.6 million viewers, 25 percent below last year's record low, according to ratings figures compiled by Nielsen on Thursday.
"Idol," which crowned North Carolina singer Caleb Johnson the winner in a two-hour finale on Wednesday night, was once an industry powerhouse for Fox, watched by more than 30 million viewers at its peak.
But it has steadily declined in ratings in recent years, averaging around 8 million viewers per episode over the current season, despite featuring celebrity judges Jennifer Lopez, Keith Urban and Harry Connick Jr.
The 18-49 demographic that advertisers covet accounted for 3.3 million of the viewers this year.
Last year, the finale garnered a low of 14.2 million viewers, the first time the show's end failed to draw 20 million people, despite bringing in high-priced celebrity judges Mariah Carey, Nicki Minaj and Urban to boost sagging ratings.
Its biggest competitor in the singing contest space, NBC's "The Voice," drew 11.6 million viewers during its Tuesday finale, down from the 15.3 million during its spring finale last year.
"The Voice," which airs in both the spring and fall each year, continues to be a ratings hit for the Comcast Corp-owned network and has outpaced "Idol," averaging about 13.8 million viewers per episode this season.
"Idol" will be scaled back for its next season from approximately 50 hours to 37 hours, Fox Broadcasting entertainment chairman Kevin Reilly said earlier this month.
Last year, longtime "Idol" producer Nigel Lythgoe was fired from the show because of low ratings and replaced by Swedish producer Per Blankens. (Reporting by Piya Sinha-Roy; Editing by Mary Milliken and Andre Grenon)