Your source is ok, I guess, its just said things in a kinda stupid way. This topic has been covered before. Every 10db increase is a doubling in SPL (sound pressure level, and I would call this loudness, colloqually (I know its spelled wrong)) and perceived loudness. 80db is twice as loud as 70db. 90db is 4x as loud as 70db (2x2=4). It takes ten times (10x) the power to double the SPL. So if you can play 90db with 1 watt, then 100db will take 10 watts,110db will need 100 watts, and 120db will need 1,000 watts. Got it. OK. So the first 4 sentences of your source are OK; its just said really weird.
He gets confused on the 5th sentence, or at least I am. If we need 60-70db dynamic range, well, to my knowledge, a bit limited, a 90db efficient speaker already has that dynamic range. It can play 90db with 1 watt so it can do 70db with even less power. What he's done is added the 60-70db onto the 90db to give a dynamic range of 150 to 160db. And from there it appears to be ok mathematically, yes you'll need 1,000,000 watts into a 90db efficient speaker if you expect it to play 150db loud. Thankfully, there are speakers w/ 100db efficiencies and higher, so we can make up for power with sensitivity/efficiency. And there's little reason to go beyond 120db because you'll start getting hearing damage. The 6th sentence is a no-brainer and his first five sentences are a little dumb, it he's just trying to support #6. Just disregard the last sentence (#7). As far as I know, loudness, i.e. how loud the system can play, is dynamic realism, the system can go from really really loud to quite. And the amount of power is in direct relation to how loud it plays once the system efficiency is taken into account. Hopefully, I'm not wrong on anything or I'll have confused you more trying to unlearn, relearn, unlearn, etc.
He gets confused on the 5th sentence, or at least I am. If we need 60-70db dynamic range, well, to my knowledge, a bit limited, a 90db efficient speaker already has that dynamic range. It can play 90db with 1 watt so it can do 70db with even less power. What he's done is added the 60-70db onto the 90db to give a dynamic range of 150 to 160db. And from there it appears to be ok mathematically, yes you'll need 1,000,000 watts into a 90db efficient speaker if you expect it to play 150db loud. Thankfully, there are speakers w/ 100db efficiencies and higher, so we can make up for power with sensitivity/efficiency. And there's little reason to go beyond 120db because you'll start getting hearing damage. The 6th sentence is a no-brainer and his first five sentences are a little dumb, it he's just trying to support #6. Just disregard the last sentence (#7). As far as I know, loudness, i.e. how loud the system can play, is dynamic realism, the system can go from really really loud to quite. And the amount of power is in direct relation to how loud it plays once the system efficiency is taken into account. Hopefully, I'm not wrong on anything or I'll have confused you more trying to unlearn, relearn, unlearn, etc.