Woofer size and power usage.

[STEvil]

I'm not sure what exactly I could point you at to clear it up any further. Maybe you need to think of it in terms of decibels versus distance (or room size, discounting construction materials/strength) from the diaphram/speaker. For example if you had an 8" driver and a 12" driver both rated at 88 decibels efficiency at 1 watt at 1 meter, the 8" driver may only reach 75 decibels at 5 meters, whereas the 12" may still be near to 80-85 decibels.