Radial variation of the azimuthally averaged travel-time shifts measured for the simulations with B_u = 1500 G and z_WD = 250 km (black), z_WD = 350 km (blue), z_WD = 450 km (green), or z_WD = 550 km (red). The columns correspond to different phase-speed filters, from lower phase speed (left panels) to higher phase speed (right panels). The rows correspond to frequency filters centered at 3.25 mHz (top panels), 4.25 mHz (middle panels), and 5.25 mHz (bottom panels). The errors bars shown represent an assessment of measurement errors of the travel-time shift differences between two models (see text).