What is the proper loudness for listening?

When instrument volume sounds like what your hear it to be like in a live environment?  Except for rock concerts which may be detrimental to your hearing at the supposed actual volume.

Some approximations are below.

Generally, an acoustic guitar will put out between 70 and 90 decibels.

Piano (normal practice): 60 to 70 db. Piano (fortissimo): 84 to 103 db. Oboe: 90 to 94 db.

Cello ranges from 82-92 dB.

Violin ranges from 84-103 dB.

Chamber music in a small auditorium range from 75-85 dB.

The trumpet can range between 80 and 110 decibels, while the trombone can peak at around 115 decibels.

A drum set and cymbals is 119 dB loud on average but can range between 90 and 130dB (decibels) depending on what instruments are being played.

Generally, 75db is more than enough for me in my room, which is still on the way to being better treated.  Once it is treated properly, I may change my mind.

At what ever volume makes you happy, but as others have said, louder volumes can produce hearing damage, so if you do play at loud to very loud volumes take frequent breaks and keep your listening sessions short.

For me, between 60 and 70 db typically. 75 db is the most I ever want or need.

I have always asked the question if one can measure dynamics by a decibel number. There is a certain point in volume that makes the music come alive. You can hear the instrument separation, you can feel the kick drum punch you in the chest, and you can listen for hours with no fatigue. Yes the room, the room treatment, and the components will all play their part but I still think there is a low and high range you can measure that will always work and achieve that sweet dynamic sound stage or nirvana. 

Yes. Another way to say it is the optimal level is the loudest you can go for extended periods without risk of damaging hearing. Dynamic peaks in the mid to upper 80s db level starts to breach into that territory. A sound meter app like decibel on iPhone is your friend! When you start peaking in the yellow zone you are where you want to be in most cases ….. beyond the green and short of red.