How Loud are these DSLs? 5CR vs 20CR

Figured I owed you all this after my phone meter topped out at 90 dB :) Some surprises. The dsl 20 is only 5 dB louder than the dsl 5 AND plugging the dsl5 into a 2x12 didn't increase the meter reading... so why does a 2x12 cab sound louder than a 1x12!?!?