DS18 ZR600.4D ZR Class D 4-Channel Full Range Car Amplifier 150 x 4 @4 ohm 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. The ZR600.4D offers a surplus of tuning options: Low pass, High pass, and Full Frequency Selector Switches, as well as Gain Knob to help tune any song to your frequency