Don't bother learning what "watts" or the 1/1000th sized unit called "milliwatt" really means. Why? Because once you come to fully understand it, you'll then come to realize that not a single manufacturer states all the specific test conditions necessary to make the number meaningful. If I remember correctly, you need to know 6 test conditions to make the "watts" number meaningful. Say a manufacturer claims their amp (could be home, pro, car, MP3 player, doesn't matter) has "100 watts" (or milliwatts, again it doesn't matter).
A) Do they mean its peak capability for a momentary transient like a hand clap in the music or its continuous output over a sustained period of time (without overheating and shutting down), often labeled "RMS" ?
B) Is this 100 watts per channel
or all the channels (2 for stereo, 5/7 for surround sound) summed together?
C) If per channel, were the other non-tested channels also pumping out 100 watts simultaneously or were they at idle so the power supply could devote all its energy to the only driven channel?
D) Into what impedance load (with either speakers or headphones)? 100 watts into an 8 ohm speaker is easy, 100 watts into a 2 ohm speaker is much more difficult.
E) At what test frequency? Outputting a 1KHz sine wave (sounding like a "beep") is much easier than a deep bass note at, say, 20 Hz which sounds more like an earthquake is shaking the house.
F) With how much permissible distortion, usually stated as a percentage in THD (total harmonic distortion)? Car amps were notorious for cheating on this one. 100 watts with 13% THD is junk compared to a clean 95 watt amp at .1% THD, yet guess which amps sell more: "100 watt" or "95 watt"?
You get the picture?
So unless all six of these test conditions are clearly stated, "watts" are meaningless. Even if you were to discover that a particular amp had 100 watts per channel, RMS, all channels driven, from 20Hz-20KHz, into an 8 ohm load, with less than .01 % THD, you still don't know where exactly that level occurs on its volume dial [no it's not at "11"
]. It's usually in the middle "4-6" area so if you encounter an unusually low volume recording, or a very quiet passage, you have some room left to turn up the gain to hear it.
As for you not going deaf from listening too loudly, it's impossible to describe over the internet what's a safe level. The time of the exposure is also critical. OSHA gives safety guidelines which may at least help:Noise exposure limits for daily activity
But how can we know what level we're getting from headphone use of a given device? That's almost impossible to answer without placing a small probe microphone in your ear canal while you're listening to headphones and see how loud you tend to turn it up. Even cheap MP3 devices are easily capable of deafening levels with efficient headphones. As I said in my previous post, if you have any after effects like muffled perception, ringing, having to say "what?" when talking to others, it's too loud.
P.S. I don't think you need to buy an amp at all. I don't have one. The other guy, StarHalo, wasn't suggesting you get one for more volume
, he was suggesting it for sound quality
. I can see where they'd be useful for some devices with "bypassable" volume controls or direct digital outs, but none of my portable gear has either so I don't think I'd benefit from one.