My, how Sleigh Bells have grown!

The Brooklyn outfit delivered an assured, muscular performance to a sold-out 9:30 Club on Wednesday that bore little resemblance to the shaky, smoke-and-strobe buzz band of two years ago.

Supporting “Reign of Terror,” their recently released second album, singer Alexis Krauss and guitarist Derek E. Miller were joined by guitarist Jason Boyer (and 12 Marshall cabinets) onstage.

But beyond widening their sound, the Bells have learned to balance Krauss’s high-pitched warble (and rock-and-roll aerobics) with brawny guitar crescendos and precisely triggered spasms of strobe lights.

The smartly paced 45-minute set included just six of the new record’s 11 tracks and placed its best one-two punch — “End of the Line” and “Comeback Kid” — at the core. Everything around those songs played like a summary of the past two years: The spasmodic hooks of “Infinity Guitars” and “Kids” felt bolder, Krauss’s stage presence smarter and sassier — her vocals clawing but never quite grating.