I still remember from back in the days when I was seriously into car stereo, if I took the smallest box that would hold two 10" speakers, I could get frequency response on the low-end equivalent to a 15" speaker (well, 14.5", actually) yet keep the tightness and response of the 10" at the upper end.
I was crossed over at an insanely high frequency for a subwoofer, (I forget now, maybe around 150Hz?) and won the Sound Quality section of every competition I entered, got totally beaten in Sound Pressure Level. Quality counted for more than noise, so I always won my power class overall.
The lowest frequency a speaker cabinet will produce is proportional to the sum of the cone areas of all the speakers in the box.The system was totally stealth, other than the funny-looking "radio" in the dash.
It was an amazing car stereo.
tanstaafl.