It's a 10 to 1 ratio with wattage anyway. It takes 1000w to effectively double the output of 100w amplifier in spl. So even with 50w you need 500w just to double the perceived spl. At least that's how it's been explained to me. Please correct me if I am wrong.
Power to volume is logarithmic, but not quite that much. Doubling the power is only 3dB louder. Double three times- 3, 6, 9dB- you're talking 8 times the power to go 9dB louder. The ten to one you're thinking of is probably 10dB takes ten times the power. That one is true.
Another factor is "double the perceived spl" that one is pretty subjective. 3dB is only a little louder, but a lot of people would probably agree 10dB is twice as loud. So that may also be where your 10 to 1 comes from.
Either way, based on what I am hearing from my Moabs its a slam dunk that Encores are super easy to drive and sound amazing.