Some basics of car audio

Don't overdo things

Don't trust your local installer

Insist on good wiring and installations

Stick to your requirements

For a small hatch back, unless you are a professional, a good quality set up would be a high voltage output head unit (preferable Alpine), with a DSP function for time alignment, a 4-channel amp with reasonable good rms (@least 75 watts), a pair of components at front driven from the two channels and one 10-inch (for a tighter bass) or 12-inch sub woofer, driven by bridging the other two channels (ensure that the amp is bridgeable)

DSP (digital signal processing): is an electronic circuitry or software used to alter the character of sound waves when they are in digital format.

Time alignment: Since we do not sit exactly at the centre of a car or equidistant between the left and right speakers, we hear one speaker more loudly and since the sound waves from that speaker reaches us first , we here the same sound from the second speaker after a split second.

Time alignment is a DSP function used to correct this oddness. Here the audio signal is spilt so that one speaker fires first and the second one fires after a millisecond giving us a perception of beting at the centre of the show