On the other hand, a parametric equalizer is much harder to adjust than a graphic EQ, requiring an experienced person and measuring equipment. The main difference between mono and stereo EQs is that a mono EQ has only one input and one output, and a stereo has two inputs and two outputs. Just turn the knob or slider and both left and right channels are taken care of. A mono EQ controls only one channel, so you need two of them for the whole system. Since you have now two EQs it takes a lot more time to setup the system.
Many people use mono EQs for the greater control they give over the system.
Since left and right speakers are not exactly at the same distance to our ears, two mono EQs can help compensate for time delays and problems caused by speaker placement. The output goes directly to the speakers and can not be hooked up to another amplifier. These equalizers are cheap and cause more damage than good to the sound system. A low level input EQ takes RCA signals from the radio and has RCA outputs that get hooked up to amplifiers. Since these equalizers work at low signal levels, they introduce very little distortion, if any to the system.