For the enhancement of toner release from an imaging surface on a flexible belt member (10) in an electrophotographic device a resonator suitable for generating vibratory energy is arranged in line contact with the back side of the belt member, to uniformly apply vibratory energy to the member. The resonator includes a horn (152) divided into a linear array of segments (158b), and an array of vibration producing elements (150a), each coupled to at least one horn segment, and driven with a voltage to produce a high frequency vibratory response. To avoid the problem of roll-off in response that occurs at the outer segments of the array of horn segments, the vibration producing elements coupled to the outer horn segments are driven with a higher voltage than those coupled to horn segments in the central portion of the array.