The frequency of a sound indicates the rate at which the sound making device is moving. A fast moving device makes a high frequency sound; a slow-moving device makes a low frequency sound. The human ear cannot hear the sounds with the lowest and the highest frequencies. The car audio equalizer has the ability to pick-up the signals from those sounds.
The owner of a car audio system wants an equalizer that can sense, that can pick-up or detect the signals from the high and low frequency sounds. Within the car audio system, the electrical signals leave the preamplifier and travel to the equalizer. In the car audio equalizer the signals loop around the processing unit and the frequencies of the signals are adjusted. The adjusted signals then travel back to the preamplifier. The preamplifier sends the adjusted signals to the amplifier.
In the amplifier, the power of the adjusted signals is increased. The high-power signals then cause the speaker to vibrate. The vibrating cone of the speaker causes it to emit sound. Because the signals have been adjusted by the car audio equalizer, all of the sounds coming from the speakers will be heard by the humans riding in the car with that car audio system. (No doubt, dogs in the car would hear those same sounds.)
