i thought that logorithmic scale was to the power of 10, so it required unit of 10 times the magnitude to double the volume.... then again its been soooo long since i've done any maths, its probably all wrong
edit: actually its the other way around, you increas the volume from 1 to 10, it doesnt increase it 10x it increases it 100x... however i think its diminishing as you increase the volume, from 90 to 100 isnt a 100x increase... anyhows, rambling, and was initially wrong, still dont think its twice as loud... =P