Polk’s super-efficient PA D4000.4 four-channel amplifier is a very cool solution.

Super-efficient Class D design—Runs much cooler than conventional amps.

High-speed MOSFET—Switching power supply.

Toroidal transformers—Help keep the amplifier’s sleek design under 2-inch tall while ensuring plenty of clean, efficient power.

Protection—Thermal, DC offset, reverse DC voltage and short circuit protection.

Nickel-plated wire terminals & RCA connectors—Ensure maximum signal transfer.

Front & rear level controls—Adjust the gain of the front and rear channels to match the output voltage from your head unit.

Low-pass & high-pass frequency controls—Enables you to adjust crossover overlap for better blending of speakers.

Front & rear BPF, FULL, HPF switches—Selects full range, high pass filter, or bandpass filter to dial in your speaker blending.

Channel mode switch (ST/4Ch)—In the stereo position, the amplifier will send the same signal to front and rear channels.

Stainless steel hardware—Used throughout won’t corrode in humid environments.