Power spectrograms (from top to bottom) of the m = 2,4,1 and 3 Fourier components for the gSa (Cols. 1, 2) and gS0 (Cols. 3, 4) models. Spectrograms are computed in a time window Δt = 1 Gyr centered on t = 0.5 and t = 0.8 Gyr. For m = 2 and m = 4, the resonance loci are plotted for the CR (solid), 4:1 LR (dashed) and 2:1 LR (dot-dashed) orange lines, computed as Ω, Ω ± κ/4, and Ω ± κ/2, respectively. For the m = 1 and m = 3 cases, we plot Ω, Ω ± κ, and Ω ± κ/3. Both bars and spirals are seen to slow down at later times. The dotter-red and solid-blue vertical lines show the radial location of the bar’s CR and OLR.