It might reflect different attitudes between cultures as to what volume makes one an "asshole".
(Sure, I just called someone random on the web an asshole. I don’t mean it with any force. In London we get people riding busses playing their im-personal stereos loudly, sometimes. I often don’t like it either. I often use headphones for my own sounds but not the blocking kind, and will have to stop my music because of thwirs. One time someone got into the Tube/metro carriage I was in playing loud Brazilian music from a speaker on a trolley. At first it annoyed me, but after a few bars it got me grooving. Then I realised it was a funk-infused cover of a traditional capoeira song, so I steuck up a conversation with the other rider about Brazil and capoeira. Made my day.)
For me, I don't want to live in a cacophony of noises 24/7. That goes for music, non-stop ambulances, loud speakers, etc.
I tried and decided that those places are not for me, so I moved back to smaller and much quieter places (I very much prefer the sound of rivers, insects and wild birds to other people's sounds.)
It might make me an asshole but it's also quite natural to be drawn to peace, so there that.
However, if you are hard of hearing to the point where you are actually disturbing others, I would recommend headphones.
If we cared more for the hard of hearing we would reduce music volumes and make restaurants quieter. Our society doesn't care even though it pretends to.
https://www.youtube.com/watch?v=HMUDVMiITOU
https://www.youtube.com/watch?v=X_IWlPHMziU
Other cultures seem to feel more entitled, thinking that THEIR music could not possibly bother anyone. I've certainly heard people blast Wagner or Orff at high volumes.
But in my experience, party intensity and music volume are generally correlated, so you would probably turn down the former by turning down the latter.
As described at Wiktionary [0] - it's an idiomatic way of saying that you're going to lower the volume through use of a control to do that. The context that was used has nothing to do with party.
[0] https://en.wiktionary.org/wiki/turn_down
EDIT: My bad, thought it was in response to...
> I guess it will mostly reflect the musical taste of assholes who turn their music up loud. Hmm, but maybe all culture works like that.
> At its core, turn down for what is a phrase used to promote having a good time. The phrase itself implies that there is no reason to turn down and stop partying.
Mine is firing directly upwards. I'm not trying to knock birds out of the sky.
A collogue:
Someone who sees their role on the team as to annoys others.
My subs, while currently pointing backwards, would have been better firing upwards for no other reason than the manufacturer (Audiofrog) doesn't recommend grills. As it is, I have to be careful what I place in my trunk to avoid punching a hole in the cone.