I'd like to add a quick comparison here. I bought a pair of K545's 18 months ago. Later i also bough a pair od beyerdynamic dt770's (80ohms). Not because AKG's were bad but because beyers were better for my needs of playing drums and "solo" monitoring channels when running live sound.
So i have had a lot of time to compare the two of these in A/B tests.
My opinions:
AKG: Just slighly lower sub response, would be a bit better for DJ's and electronic music compared do the beyers. The difference is very small.
BEYERS: Definitley better low-mid. They sound warmer, richer, more natural. That 150-400hz segment where balls of distorted guitars come is better on them. However. beyerdynamics are famous for their phenomenal mid-range response so this is quiet expected. It's not such a huge difference but you can hear it. Because of this, when you put akg's on yours head after listening to beyers for a while, they sound kind of empty. I don't know how to describe this in a better way.
High-range: There is kind of, more of it on akg's. The entire 3k-16k spectrum is kind of brighter on AKG's. You can hear how vocals, cymbals and the upper end of electric guitars (presence) jump out in the mix a bit more then on the beyerdynamics.
I'm not however saying this is a good thing because i'm not saying the beyerdynamics sound muddy because of lacking highs. They sound more natural to me then the AKG's.
These highs give the AKG's a more plastic sound and they even become harsh when you run them loud.
The differences are however not that big as i might sound like when describing them. It's just that beyers sound flatter and more natural to me, overall. They also have a better soundstage. And they are made in Germany. The akg's are from China.
Those are my opinions. Also i'm selling my AKG's but i live in Croatia so i dubt that information will be of any use to you here
