dman77
For every 3 db SPL increase in output volume requires a doubling of the amplifier watts being used. So if your speaker sensitivity is 88 db, which means that it takes 1 watt of amplifier power to drive that speaker output to 88 db at 1K Hz measured 3 feet away. It will take 2 watts to drive it to 91 db, 4 watts to get to 94 db, 128 watts to get to 109 db and 256 watts to get to 111 db and that is before we consider the effects of the inverse square law which states that you will loose 6 db of SPL for every doubling of distance from the source.
To answer your question more directly, it’s a combination of amplifier power, speaker sensitivity, source level, room size, music type (low frequencies will eat more power than high) and I’m sure there are other factors I don’t know about. A 200 watt amp is a 200 watt amp and will drive a speaker close to the same volume regardless of price, but a better amp may do it a little cleaner, with better low end or better peak output, etc. etc.