Our Project Car, the Corvette C5, is equipped with GM's premiere sound system. Its performance is well above your average car. However, it doesn't begin to compare to the quality aftermarket systems that are available.
Things to Remember
Here are a few things to keep in mind when comparing car audio and home audio:
The C5 Corvette
The head-unit in the C5 is a Delco CD player with changer control. It has large buttons and plain styling. The Bose Speaker System here is very odd, as there is a proprietary connection from the head-unit to each speaker. At each speaker there is a small amplifier. This makes upgrades of the rest of the system almost impossible without replacing the head-unit, which for our cause is just fine.
The head-unit supports CD, CD-R, and has changer control for the factory changer. Note that the changer doesn't fully support CD-R. One feature that is nice is the SCV (Speed Compensated Volume). SCV raises the volume as you drive faster, so that the music appears to have a constant level. Very handy for convertibles.
Due to the proprietary connection, there is really no way to bench test the small Bose amps. There is a single amp in each door powering the 8" mid-bass. The 3" driver is powered from the deck. The Bose amp appears to be a class D design. We were able to get about 18 watts out of one of the amps, measured by voltmeter. However, 18 watts probably isn't the max, as the measurement was taken during the "best THD at 500hz" test.
Each door houses an 8" mid-bass and 3" full range (!) driver. The 8" driver uses an inverted magnet structure to reduce depth. The lack of a tweeter is very apparent in the system, as the 5 kHz range is very undefined. The 8" driver goes into heavy distortion on any signal lower than 40 Hz at any meaningful volume. Overall, the system severely lacks punch. With no tweeter, and running at 15-18 watts per channel, the sound isn't crisp, and it lacks detail. The mid-bass is muddy, and vocals are harsh.
There is a low SPL limit to the factory system. The frequency response was taken at 100 dB. Trying to push past that SPL generated large amounts of ringing in the THD tests. When you subtract the road noise level from 100 dB you get a good idea of your system's dynamic range. Now, you can increase that by going louder, or by making the car quieter. Since I value my hearing, we are taking the second approach.