Pioneer GM-D8701 (D class) power amplifier (mono).

Pioneer GM-D8701 (D class) power amplifier (mono). 

Pioneer’s extra-efficient Class-D amplifiers mark a dramatic improvement in power output capability, yet are 50% smaller than the current GM-Series Class-AB amplifiers.
That makes them more versatile in terms of installation as well as performance.
To prevent circuit shutdown, Pioneer's digital amplifier circuit "Protection Control System" senses its internal temperature and automatically moderates input level accordingly. 

Stable, durable circuitry lessens the risk of high input power for the unit to achieve 1 Ω connection. 
This design enhances the flexibility to connect multiple subwoofers to a system.
For extra flexibility, a variable LPF makes audio frequency more adjustable according to subwoofer characteristics and personal listening preferences.