This paper presents a comparative study based on a thorough beam bending test.The intention is to obtain the relationship between the nominal elastic wave velocity obtained from Acoustic Emission tomography analysis and the physical damage of the RC beam in terms of crack opening. The crack width of the specimen was determined by both Digital Image Correlation and the conventional LVDT measurements. The study shows that globally the nominal wave speed derived from AE tomography is related to the crack development of the specimen when the crack width is limited. It is also shown that the scatter of the AE tomography results can be improved by averaging the nominal wave velocity of the cells along the cracked section.