We report the design of quasi-two-dimensional artificial structures that acoustically behave as positive, single negative, double negative or density-near-zero metamaterials. The scattering units consist of a cavity drilled in one surface of a 2D waveguide and they have an inner structure whose geometrical parameters can be selected in order to obtain the desired dynamical behavior. Finally, we report the practical realization of two samples as well as their experimental characterization showing metamaterial features.