This paper presents the effect of input source energy on the results of spectral analysis of surface wave (SASW) evaluation of flexible pavements in terms of maximum and minimum wavelength. A series of surface wave tests, namely the SASW test, were done on asphalt pavement using four steel balls with different masses as sources. These sources were dropped from two different heights, 0.25 and 0.50 m. This test was also conducted with two different configurations, i.e. with the receivers positioned 0.15 and 0.30 m apart. This paper also presents the feasibility of using accelerometers to measure flexible pavement deflection. For this purpose, the process of integrating accelerometer time history is described. It is proved that a change in input source energy has some effect on the value of maximum and minimum wavelength. The result for numerical double integration is satisfactory and is congruent with the displacement obtained through finite element analysis.