The dynamic mobility spectra of several colloidal systems having a ratio of particle radius to double-layer thickness between 1 and 20 have been measured using the technique of electroacoustics, Good agreement is found between the experimental mobility spectra and the theoretical spectra generated by the computer program of Manglesdorf and White for spherical monodisperse suspensions with sizes in the neighborhood of 0.1 mu m. Smaller and larger particles show some minor discrepancies which are more likely to be due to limitations of the model systems being used for the test than to any basic limitation of the theoretical analysis.