Speed of ultrasound in liquids measured at a constant acoustic pathlength. Comparison and discussion of errors

Abstract
The phase speed of an ultrasound wave is a significant source of information, however, a significant problem are discrepancies in the speed of ultrasound values quoted by various authors, which often exceed considerably the declared accuracy, i.e. the values available in the literature are not consistent. This is due mainly to the application of different measuring methods and their "inherent" systematic errors. In this report a comparison of two, dominated almost entirely laboratory practice, pulse measurement methods with a constant acoustic pathlength, i.e. the sing-around method and the pulse-echo-overlap method is given basing on literature data and our own experience (sets designed and constructed in our lab). Among other things, the role of a standard (in practice, only water is widespread and unique standard) in relative speed of ultrasound measurements is analyzed and a way to rationalize the measurement errors is suggested.