Gravity Equalizer 1/2 Din 9 Band 9V Car Audio DSP EQ Front, Rear + Sub Output

The function of a car equalizer is to adjust the audio input signals to achieve optimal sound quality. There are varying types of equalizers depending on the number of audio bands each change. If you’re a person fed up with a low-quality audio player, then a car equalizer may be just what you need.

eBay