Headphones: AKG K240s vs. K240DF vs. Beyer DT990pro

I don't know the Beyers, but the K240S is a little too bright to be realistic.. at least to my ears. The DF is a bit more natural, but the bass in both isn't quite realistic as it seems to be lacking compared to speaker playback. They are both excellent sounding headphnes IMO. I have my doubts that there is a pair in the world that are realistic enought to mix on, even in the frequency domain alone, but I haven't heard all that many, so...

i agree with dave!
i have a k240df and when i mix with them the bass frequencies are way different than the result in speakers! i've came to learn the differences between! this sound great! but they're not that realistic!

is there a difference in the sound of the k240df and k240s?

Yes. but you may not be able to hear the difference. The 240DF are the same but are tested to tighter tolerences. All those that fail the tighter testing become regular 240 headphones. I have both and have them for more 15 years and the difference is subtle. I really like them both and have become so used to them that I can even mix with them with very good results.

"Bright" is not how I would describe the K240s. I actually consider them a bit on the dark side - granted the other headphones I often wear ARE bright (Grado SR80). I tried Sony 7506s when I bought the AKGs and they were WICKED bright - harsh.

The K240s work well for me as honest cans for monitoring.