An ultrasonic horn assembly includes a horn with a bore tapering from a throat out to a mouth. An ultrasonic transducer is mounted in the throat of the horn. A beam narrowing insert includes a headpiece which tapers smoothly from a larger diameter base to a smaller diameter top. A stem projects from the base so that the base and stem define an annular shoulder which faces the transducer. A blind bore in the stem terminates at a flat bottom surface which faces the transducer. A ring receives the transducer and webs project inwardly therefrom to support the headpiece in spaced relationship to the transducer.