LOS ANGELES - 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 audience, 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 latest season, despite featuring celebrity judges Jennifer Lopez, Keith Urban and Harry Connick Jr. The 18-49 demographic that advertisers covet accounted for 3.4m of the viewers for this year’s finale, down from last year’s 6m. Early Nielsen ratings data on Thursday from Fox said total viewership for the ‘Idol’ finale was 10.1m, with 3.3m in the 18-49 demographic. Last year, the finale garnered 14.2m viewers, the first time the show’s end failed to draw 20m people, despite bringing in high-priced celebrity judges Mariah Carey, Nicki Minaj and Urban to boost sagging ratings.