A transducer comprises a longitudinal tubular member symmetrically disposed about a central longitudinal axis, the tubular member having a slot extending from the front end of said member to the rear end of the member, the slot extending parallel to the central longitudinal axis; a stack comprising a single element or plurality of vibratory elements arranged from a first to a second end and; a mounting arrangement for mounting the said stack across the inner wall of said tubular member on a line relatively transverse to said longitudinal central axis. The mounting arrangement includes a layer of solid lubricant engaging opposite ends of the stack, enabling the stack to move in a direction of the central axis when the stack exhibits vibratory motion.