As the smallest amplifiers in their class in the world, the XR-400-4, KAC-X1D mono amplifier and KAC-X5D five channel amplifier - overcome thermal radiation issues inherent to compact amplifiers and pack powerful Kenwood technology into a small form that enables installation in tight locations previously restricted to lower performance amps. This is ideal for users who do not wish to sacrifice boot space or prefer stealth installation. Excelon Performance & Quality - eXcelon products incorporate the latest technologies and deliver the highest sonic performance. From advanced audio tuning capabilities, crossover and equalizer systems, high voltage preouts and two-year warranty, eXcelon represents the very best product available.Small Footprint Design - Reference-Fit amplifiers are Kenwood"s best sounding amps and have one of the smallest footprints in their class, making them the perfect solution for vehicle installation where space is at a premium. This compact size was made possible by the development of a high-density mount circuit board in conjunction with an enhanced air cooling and heat control systems. Kenwood"s created a compact amplifier that enables installation in tight locations previously restricted to lower performance amps. This is ideal for users who do not wish to sacrifice space or prefer a stealth installation.Air Cooling - By positioning the fan in close proximity to heat producing circuitry, heat is dissipated efficiently. This allows the amplifier to