Abstract: The tandem cable is a crucial component in long-span bridges, characterized by intricate aerodynamic disturbances, particularly prominent in wind-induced vibration issues. This study performed experiments on three differently scaled models, investigating the free vibrations of tandem cables in subcritical, in critical and, in supercritical Reynolds number environments, the study focused on scrutinizing vibration response characteristics and on the efficacy of aerodynamic interventions. Study results indicate that the maximum detrimental center distance of amplitudes primarily concentrates within the range of 2.5~4.5 times the diameter. Free vibrations of tandem cables exhibit notable Reynolds number effects, with minimum structural vibration responses observed in subcritical conditions. Conversely, significant wake galloping and vortex-induced vibrations manifest in critical and in supercritical states. At subcritical Reynolds numbers, helical ridges and rough surfaces aid in suppressing cable wake vibrations, yet under supercritical Reynolds numbers, a helical strake may induce substantial downstream cable oscillations.