I think having an efficient loudspeaker is important. Usually efficiency i measured in db at 1 meter distance from the speaker, receiving 1 watts. But since a speaker has a variabel impedance vs frequency, this has later changed to 2,83 volts input. at the frequncy the speaker is 8 ohm, this vil give 1 watt. If you have 4 ohm, 2.83 volts vil give you 2 watt. So this means that a 99 db/W 8 ohm speaker is as loud as a 4 ohm 102 db/w speaker. Statement 1: After having tried some different speakers the 15" always seems louder, even when they are rated at the same SPL and have the samme lower frequency range than a 2 x 10". This is even more apearent, when i compare an older Peavey 15" with newer 2 x 10" systems. I got the samme impression about 15" vs 18" in PA. the 18" always seems so loud. Even when the 15" had the samme -3 db point. This makes med wonder, when the manufacturer measures his speaker: at what frequency is this done ? Could it be that let's say a 4 x 10" system is measured at let's say 500 hz ? And a 15" at let's say 100 hz ? (A smaller speaker like a 10" , are usualy a lot more efficent at higher frequency's than a 15") Statement 2 : The lagest cabinet always seems to win. And this makes me also wonder if the SPL of the driver is measured in a very efficent cabinet, and then later, this data is used on the smaller cabinet. ? Or is it there something i have missed about the larger cone " Of 15" gives a higer SPL in smaller roms (at lower frequencys) ?