A car interior is probably the absolute worst acoustic environment for an audio system.
Consider the issues-
Road noise and vibration and bass cancellations.
Road noise, wind noise, powertrain noise vs. amplifier head room / power requirements.
Charging circuit and voltage vs. amplification requirements.
Door cavities make poor speaker enclosures.
Greenhouse glass is a highly acoustic reflective surface and will alter the polar response from upper speakers requiring extensive EQ to tame.
Every OEM mobile audio system has embedded EQ curves to compensate for the above. Some do a good job, some do not.
Consider the issues-
Road noise and vibration and bass cancellations.
Road noise, wind noise, powertrain noise vs. amplifier head room / power requirements.
Charging circuit and voltage vs. amplification requirements.
Door cavities make poor speaker enclosures.
Greenhouse glass is a highly acoustic reflective surface and will alter the polar response from upper speakers requiring extensive EQ to tame.
Every OEM mobile audio system has embedded EQ curves to compensate for the above. Some do a good job, some do not.