RX-DP20VBK/RX-DP15 -- Copper-Plated "High-Rigidity Z-Chassis" The rear panel, brackets and bottom plate are copper-plated to prevent interference between mounted circuits, reduce chassis impedance, and stabilize the potentials of voltages of low to high frequencies. Moreover, a reinforced design called 'High-Rigidity Z-Chassis' is used for zero vibration, zero resonance and zero interference to ensure highest fidelity.