Why magic at 80 db?

I live next door to Bob and I really wish he'd turn his damn speakers off. They've been on 24/7 for almost a year!

Doesn't the listening level depend on your mood, the type of music, the time of day, the ambient sound level in the room (cat snoring, young starlets calling my name from the hot tub outside), and humidity? (I tossed that one in). I have one of those Studio Six iPhone SPL meters (they claim it's WAY better than the Shack meter...but then why wouldn't they?) and it's almost interesting to see what playback level I need. I discovered I'm all over the map, my speakers sound great at low levels (surprisingly), and I still practice electric guitar a bit too loudly (albeit with a 5/15 watt tube amp...so sue me...my "Bob" revenge).

Wow, you guys are pretty low... must have significant others or neighbors that keep you in line!

My systems have always been very dynamic meaning there's a large variation in volume from the softest to the loudest sounds... This does require that you play at a fairly healthy average level in order to not lose the softest sounds. The effect is that the greater the dynamic range the lower the relative average level seems. Those who claim otherwise simply have a lot of compression going on in their systems whether they know/admit it or not. Another factor that can determine how loud you need to play your music is the ambient noise level in the room. The higher the ambient noise, the higher you're likely to turn the volume. It's simple science. Whether that's good or bad is all in how you view it.

But I like my big/good system to duplicate the kind of dynamics I hear live whether amplified or non-amplified (sometimes a little less)... and both these levels are far lower than what you are subjected to when you visit your typical movie theater, which surely play at a level sure to cause hearing loss. I always need to bring ear plugs to enjoy a movie in a theater. Why more people don't complain about these ridiculous levels (or bring along some type of ear protection) is beyond me. Could be some really big class-action law suits out there waiting to happen.

Many good posts. The better the system with less noise and distortion the better it will sound at both low and high levels. And everything in between.
I'd say, yeah, my system too sounds best at probably 70db-80db. Go louder - significantly more distortion, go lower - lose something. But my amp is not so good; with better amp it would be somewhat different. Still, the figure of 80db sounds about right to me.
Software matters, that's for sure.

Rodman99999-Thank you very much for the website digido. A wonderful lesson in mastering and re-mastering regarding loudness levels. A bookmark for sure.

To follow up, here's some extended discussion from a mixing/mastering forum concerning how to set an 83db "reference level", how fatigue plays out at that level, different opinions regarding the potential for hearing damage based on time of exposure, etc. You guessed it, there's a forum for everything. If you're interested, you can also find extended discussions of mastering styles and theories, the benefits and evils of "compression glue", and all manner of other stuff that goes into the decision tree behind any given track. Personally, spent a bit of time digging into this stuff recently, but ultimately decided that ignorance is bliss on this one. (Figure I enjoy sausages a whole lot more for not knowing how they're made, either. But that's just me.)