Xaver, there are two different topics.

1. When you are talking about noise: in the sound/acoustic engineer field we talk about and reference the NC - NR curves, and it depends of the level of noise in dB in any space and the purpose of that place.

2. When you are talking about "the comfort of listening" here are others values to take on account, the %ALCONS, the intelligibility, critical distance, definition, clarity, intimacy, Knudsen method and others basics like reverberation time.

Thanks David,

Interesting point from the engineering field! I would be interesting to relate these objective measures to the subjective measures I was talking about.

Best X.

To expand upon David's answer, the clarity and speech intelligibility measurements (particularly those defined in ISO3382) used in some branches of environmental acoustics are regarded by some (such as Riesinger) as unfit for purpose as they are based on perception of simple signals such as sine waves, rather than complex signals such as actual speech. 

To the best of my knowledge, no one has yet tested whether ANLs are related to listening effort.  I only know of two papers—both very recent--that have investigated the cue underlying ANLs (below). For most people, it is still unclear what criterion they are using to determine their ANLs.  I think testing whether there is a relationship between ANLs and listening effort is the next step in this field. 

Gordon-Hickey, S., Morlas, H. (2015). Speech recognition at the Acceptable Noise Level. J Am Acad Audiol, 26, 433-450.

Recker, K., McKinney, M. F., Edwards, B. (2014). Loudness as a cue for acceptable noise levels. J Am Acad Audiol, 25, 605-623.

Thanks Karrie,

Of course I know the publications you're citing. Both are very interesting. Thanks for your answer - it makes me even more self-confident that our (Koch & Janse) current study  will contribute insights to the literature. 

X.