Polk Audio Dxi400 The DXi400 is an easy install in a door or in a dash. Its compactness makes it an easy fit, but it's big on all the Polk technology that makes it uniquely DXi: Legendary Polk sound at a terrific price. Dynamic Balance driver technology for pure, distortion free sound. Composite cones feature tremendous stiffness-to mass ratio. Lower mass means faster transients and finer detail. Klippel optimized components for consistent, distortion-free sound. Marine Certified means the DXi460 is built tough to withstand the harshest environments on the water.