Abstract: Methods and apparatus are disclosed for applying acoustic energy to the skin. Acoustic waveguides with elements of varying thickness or shape are disclosed which deliver energy to more than one depth below a surface of the skin substantially simultaneously. The invention is especially useful with devices that focus ultrasound energy by condensing a propagating wavefront. The invention compensates for the mismatch in acoustic properties of the device's waveguide and the biological tissue that typically cause portions of the collapsing wavefront to lag behind other portions and, thereby, limit the focusing capabilities of acoustic treatment devices.