If you're like me, then you probably spend hours and hours researching different products, comparing the prices and the pros and cons of many products. Headphones included. For me, I have had a set of AD900x headphones for a few years, and the cable gave out, so I opted to try a new set of headphones. It was down to 3 choices within the same price range, all open back. The Sennheiser HD599, The Beyerdynamic DT990, or just settling for another pair of AD900x's. (Sadly couldn't really consider anything AKG because every model I saw in the same price range required an amp.) I don't know whether to call myself an audiophile or not, but I would like to say that I pay very close attention to sound, and its very important to me. Perhaps the most crucial part of a headphone for obvious reasons. I'm not a professional, just an average guy that loves/has good sound equipment. I would like to offer some clarification, at least that my ears have heard, as I have had the opportunity to own all 3 sets due to some circumstances that Ill discuss later. Here's a comparison with the 3 different headphones I was in the market for.Sennheiser HD599: Pleasant.These headphones to my ears are designed to sound pleasant, not necessarily accurate. At first I was worried about that, especially hearing about the signature "Sennheiser Veil" That everyone talks about. I'm pleased to say that despite my worries, they did an amazing job with what they were marketed for. They do have a small "Veil" That some people may or may not like, but the veil is essentially to my ears a cut in the high mid frequencies. These are the frequencies that are very harsh, and the high highs are still perfectly sparkly and sounded very nice. I found myself going to these headphones for relaxation and for pure enjoyment. You could definitely fall asleep wearing them as many have said. I recommend these headphones for ones that want to relax or have a "milder" sound with their setup. To my ears they seem to have the most bass out of the 3 as well. Again, I was afraid I would not like them because I was afraid that I would not like the sound signature of them, but I was very pleased. Unfortunately, I had to return them due to a defect which made the balance shift to the right side that made it louder. They were a used set, which is something to keep in mind.AD900x: Natural.The best selling point of these headphones in my opinion are their soundstage. Its the best soundstage I've heard out of the 3. And they also to my ears have the most neutral tuning out of the 3 headphones. They are also incredibly comfortable, despite their "gimmicky" Headband design, I actually quite liked them a lot. As much as 4 years worth to be exact. This design made them very light, so many times I would forget that they were on my head. I find myself using these headphones if I want to feel like I am in the room with whatever I'm listening to. They had enough treble to get the job done which I enjoyed. The bass is also there, although a little light. I feel that with the amazing soundstage, some detail had to be sacrificed, including the bass. Which isn't necessarily a bad thing. I recommend these headphones for ones that want the most neutral sound out of the 3, and who want superior soundstage, who don't mind a small loss of detail. Like feeling like you are actually walking through that forest, or that you're actually there listening to the orchestra.DT990: Detailed.It seems that these headphones are designed mainly for studio production. And if that's the case, I wholeheartedly recommend these headphones, which is what I'm currently using now. The ones that I got were the 80 ohm edition if that matters. I have it plugged straight into my motherboard. These headphones offer the most details out of the 3, which I really like. Due to the defect in the Sennheisers mentioned above, I decided to try these. I was very worried about the treble response that everyone keeps complaining about, but decided to bite the bullet, as I could easily EQ it out. I'm pleased to say that for my ears, that is not an issue. In fact, if people hadn't been complaining about it, I probably wouldn't have noticed it. Yes, they are nice and bright, but I like them. Its like a speaker with tweeters vs without. COULD it be harsh? I suppose perhaps, but its not so much making the treble overwhelming, more so reproducing it much more effectively. Again to MY ears. If I want to hear exactly where my opponent is coming from, or exactly how loud I should have a certain track in my mixes, or even just listening for things I haven't heard before in songs I like a lot, I find myself using these headphones. I also find these headphones to have a better bass response then the AD900x's. I recommend these headphones for anyone that wants to hear every little detail of whatever they're listening to, especially useful for producing or mixing audio.Conclusion: My personal favorites are the DT990s for their excellent detail in their sound. They are also extremely comfortable due to their amazing ear pads. But you cannot go wrong with any of the above mentioned sets. They are all excellent sets, and do what they are made for, and do it well. If you have a preference having one feature over another, then I recommend going with the headphone that suits your need the best. But i will say the DT990s have a build quality and sound quality to my ears that is hard to match.Nutshell:Sennheiser HD599: ComfortAudio Technica AD900X's : SoundstageBeyerdynamic DT990s: DetailsHope this was able to help everyone who reads this. I had many questions and hopefully this can help others who have similar questions. Cheers!