It's not so crazy just a bit a science. A car speaker might be in the 90-92 dB per watt range. While a "guitar" speaker is around 100dB per watt range. The ~10 dB makes a HUGE difference. Hence the need for 10 times the power.
um... in case anyone cares I think my question has been answered
one thing though.... can anyone tell me if a 50 watt 1x12 combo amp with a 1x12 extension cab is as good as a 50 watt head with a 2x12 cab?
I cant think of any reason it wouldnt be, it's just that everyone seems to talk about 2x12's and 4x12's here which is not really what I'm thinking of. The question probably sounds stupid but I just want to be sure I am understanding this issue right.
I talked about this with my amp tech a while ago. He explained to me that 2x12 will always sound louder than 2 1x12s due to the two speakers resonating on the same baffle together. Apparently getting the speakers onto the same baffle is worth 2-3 db. With 4x12s, the results are even better. That's the whole reason multiple speaker cabs came into being. Hope that helps.
A 4x12 cab will sound louder and bigger sure but just remember....when Jim Marshall made those first 100 watt amps the most any one speaker could handle was about 30 watts. Thus the need for at least 4 speakers to handle all that power if it was cranked up.