Not only that, but the neodymium magnets from today are a major improvement over the AlNiCo ones from yesterday. This helps enormously with the cone damping.

Also, the quality of the speaker's winding and the cone's material and adhesives used in its manufacture.

 

This is kind of a self-test for me, so I'm not googling the answer ... what I remember is that the low-frequency waveform tends to get clipped at its top and bottom if the speaker's diameter is too small.

Correct, because the smaller it is the larger the excursion to produce the same amount of noise (and it's square law)

 

But if you wanted it loud, then you would build a horn, not a direct radiator. Most of the input power will be used moving the cone and suspension, rather than the air in front of it. At a guess, the cone will have to be thicker than the cone of a smaller device, so the mass will increase by the cube of the diameter, but the weight of air it move will only increase by the square.