The velocity or speed of ultrasonic energy in moving webs of material is measured on-line as the webs are manufactured by engaging and preferably scanning a measuring head over the web of material. Improved ultrasonic energy transducers are employed wherein a material contacting member is secured to an interface region between oppositely operated first and second regions which intensify and amplify the movement of the interface region and hence the material contacting member by operating in a push-pull mode relative to the interface region. The transducers are calibrated by means of reference paths having known ultrasonic transmission characteristics which reference paths are separate and apart from the web of material which is being measured. The transducers can be selectively contacted with the web of material or not under the influence of vacuum which is applied to a measuring head into which the transducers are installed. A large plurality of ultrasonic energy signals are received by one or more receiving transducers and digitally integrated or summed and averaged to eliminate substantial noise which is present on the received ultrasonic energy signals due to the relative motion of the transducers and the web of material being measured. The travel time between the transmitting transducer and the receiving transducer or transducers is then combined with the distance or distances therebetween to arrive at the velocity or speed of the ultrasonic energy in a web being measured.