In my field we use prescribed modal damping, thus alpha and beta are chosen so that the modal damping for the relevant modes of vibration are close to the prescribed values (alpha and beta are not material properties). I you want the modes between 1 and 5 Hz to have more or less 1% damping, you can set alpha to 6.1e-1 and beta to 0.12, because that will give you a damping between 0.9% and 1.1% in the area of interest