Real world limitations don't mean the theory is false. I think the problem that you're having is that you're discussing almost inverse functions which is confusing. Your power is gaining at a rate of 2^x, while the dB scale gains at a rate of log10(x). So yes, you can apply the rule anywhere and it still sticks. The problem is that in the real world, most speakers who have RMS ratings of 1000W and are producing 140dB of output won't produce 143dB of output with 2000W because that exceeds their thermal power handling. You're including real world specifics with mathematical theory which you cannot do.Regardless; you can apply the +3dB upon doubled power at absolutely any starting point. So even if your woofer is seated in an efficient SPL enclosure that rates 100dB-50db @ 1W--as seen in the second example--this principle still falls on it's face once that curve begins to bend to the right.
