DS18 ZR800.4D ZR Class D 4-Channel Stereo Full Range Amplifier 4 x 200 @ 4 Ohms Watts RMS DS18’s ZR series of amplifiers are guaranteed to supercharge your sound system to deliver brilliant sound and bulky bass frequencies. The ZR series was designed to pump up the bass and help your speakers reach their maximum potential as a part of your sound system. These amps offer a surplus of tuning options: the ZR800.4D comes with Lowpass, and High Pass filters to help tune any song to your frequency