That graph makes it seem like you should never need 120db's worth of power because your hearing should not ever be subjected to anything as loud as 120db.It depends if the SP2000 has a good Current (mA) delivery at low impedances. Power isn’t just about total Watts. The lower the impedance the more difficult a headphone is to drive for a given sensitivity. It’s easier to push Voltage to a transducer than have enough Current. This is why some gear is Current limited and can’t perform well driving low impedance transducers. You may see an amp spec that shows lower power output in to lower impedances. This most likely is a Current limited amp.
A good guide to power requirements was posted earlier in this thread. If you can get the mA and V output specs of the SP2000 then it would be easy to correlate with the graph in the post below.
But i dont think thats right..
Some dynamic transients can be even 50db higher than your average listening level, reaching up to even 130db.
The thing is, these transients last only a very short amount of time.. just a few milliseconds.
At that point, it does not damage your hearing. And your ears do not percieve it to be as loud as you might think.
But it fills out the dynamics and makes them more realistic. Clipping them by not providing enough power can negatively impact the quality of the sound.
Now, you aren't going to be seeing dynamic transient peaks that high in most songs, but for high quality well recorded songs especially in certain genre's, you can reach much higher then 120db.
Have a read of this article from Audeze it explains this in depth: https://www.audeze.com/blogs/technology-and-innovation/sensitivity-impedance-and-amplifier-power