We have calculated synthetic opacity sampling spectra for carbon-rich Asymptotic Giant Branch (AGB) stars based on dynamic model atmospheres which couple time-dependent dynamics and frequency-dependent radiative transfer, as pre- sented in the third paper of this series. We include the molecules CO, CH, CN, C2, CS, HCN, C2H2 and C3 in our calculations, both when computing the atmospheric structures, and the synthetic spectra. A comparison of the synthetic spectra with various observed colours and spectra in the wavelength range between 0.5 and 25 µm of TX Psc, WZ Cas, V460 Cyg, T Lyr and S Cep is presented. We obtain good agreement between observations gathered at different phases and synthetic spectra of one single hydrodynamical model for each star in the wavelength region between 0.5 and 5 µm. At longer wavelengths our models show- ing mass loss offer a first self-consistent qualitative explanation of why a strong feature around 14 µm, which is predicted by all hydrostatic models as well as dynamical models showing no mass loss, is missing in observed AGB carbon star spectra.