While Calvin Harris had a pretty good career going already as a dance-pop singer and producer with two albums and a fair number of hits under his belt, his 2011 collaboration with Rihanna on “We Found Love” gave his profile a stratospheric boost. On 18 Months, so titled because that’s how long it took to be made, Harris steps away from the microphone for the most part in favor of a cast of famous friends and acquaintances to create an album that plays like 50 minutes of mainstream radio pop. The basic template of the album’s sound can be found in “We Found Love,” with its melancholy and romantic lyrics, impassioned vocal build-ups, and pounding techno beats all coated with layers of shiny synths. The success of each effort rests on the vocalist and how well they can fit their style into the Harris sound. For example Ellie Goulding’s icy innocence on “I Need Your Love” works far better than Florence Welch’s desperate wail that pushes “Sweet Nothing” over the top. Elsewhere, Kelis’ sassy and assured work on “Bounce” is fresh and fun, and Ne-Yo’s smooth croon complements “Let’s Go” perfectly. 18 Months shows Harris to be a solid producer with an easily identifiable sound.