Car speakers and home speakers might have similar output ratings but the results can be very different. This is why any random speaker designed for home use might not give the best performance when used inside a car. There could also be differences in the overall design.
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The first look
The appearance itself can be very different for two similarly rated speakers used in cars and those used at home. Car audio speakers might often come with in-build subwoofers or even when there are separate subwoofers there are elegant casings provided for them. Instead of generic designs, these are done to complement the car interior design.
Audio system at the core
The car audio system might have similar connectivity features as the home audio system. But the output can be different. This, in turn, can impact the performance of the speakers. The speakers and the audio systems for the car are built with the difference in the power outlet available inside the car.
Given the higher current ratings and the lower voltage ratings in the car speakers, they are very much different from home speakers. The ideal values of impedance in most car speakers would be around 4 ohms. The impedance values of home speakers tend to be on the high side. When this value is high then the effects on the connected equipment like amplifiers and speakers can all be different. This is why you might not be able to use most of the home speakers in a car setup.
Given the smaller space where the car speakers work the space optimization of the output might also be very different in them.