It is ridiculous to say that one needs a particular amount of power, without reference to the particular circumstances. Take a look at this:
- Typical home loudspeakers have sensitivities of about 85 to 95 dB for 1 W @ 1 m—an efficiency of 0.5–4%.
- Sound reinforcement and public address loudspeakers have sensitivities of perhaps 95 to 102 dB for 1 W @ 1 m—an efficiency of 4–10%.
- Rock concert, stadium PA, marine hailing, etc. speakers generally have higher sensitivities of 103 to 110 dB for 1 W @ 1 m—an efficiency of 10–20%.
https://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sensitivity
Keep in mind, those are
typical, not giving us the extreme limits. But I will confine my examples to what is mentioned there. And I will use the calculator you provided in your link.
If you have a pair of speakers that will produce 85dB @ 1 W @ 1 M, at 10 feet with 100 watts, you will have 98.3dB (again, using the calculator to which you provided a link, selecting "away from the walls"). But if you have a pair of speakers that will produce 110dB @ 1 W @ 1 M, at 10 feet with 100 watts, you will have 123.3dB. With that second speaker, no sane person is going to need more than 100 watts at such a distance, especially if we are considering continuous power.
The long and the short of the matter is this: The amount of power needed is a function of several things, not least of which are the particular speakers used.
In the real word, with my home theater, I have a receiver rated for 140 W RMS per channel (into the rated impedance for my speakers) and speakers with a rated sensitivity of 88dB @ 1 W @ 1 M. I sit about 8 feet from the nearest one. It plays more than loud enough for me. And I used to drive the same speakers with a receiver rated at 75 W RMS per channel (into the rated impedance for my speakers), and it played more than loud enough. (If you do the math, you will see that it will be less than a 3dB difference per channel between the old receiver and the new one.) Of course, I have no idea what peak power I have used, as I do not have power meters that would tell me such a thing (most such meters in amplifiers, by the way, are not accurate enough to know this sort of thing anyway).
Of course, some people wish to listen to music at levels that cause permanent damage to their hearing, and so their requirements will be different from someone who wishes to continue to be able to fully enjoy music throughout a long life.
