He has only read reviews but have not heard em in real world with different sources,his comments are his proof!Somebody commenting about the bass of an ATH-50 being boomy should be taken as a joke. On a serious note I would say its detailed, refined , balanced ( unlike the senns) and smooth with good bass range which is deep with superb Q slope and not overpowering at all in any stage and any case.
I don't need to hear them personally, the people who do these reviews are experts and unlike amateurs like us make their living out of it.I have a lot of high end IEM's and Headphones like the Klipsch Image X7I, Shure SE 215, Klipsch Image S4, Sennheiser HD 202 and the Sennheiser HD 558 and most of them were brought on recommendations from these reviews.I don't regret a single purchase.
Coming to the Frequency response graphs of the ATH M50 and the Sennheiser HD 558, this site has them both.
M50 : *headphones.reviewed.com/content/audio-technica-ath-m50-over-ear-headphones-review/sound-quality
HD 558 : *headphones.reviewed.com/content/sennheiser-hd-558-on-ear-headphone-review/sound-quality
Quote from the sound quality section of these reviews.
ATH M50 :
As you can see from the chart below, the frequency response of the ATH-M50 was a little more dynamic than what we usually like to see, but for some people the overemphasized bass and subdued 5-10kHz ranges might be preferable to other headphones. Audio Technica seems to have frequency responses very similar to this one in other models they've fielded, but this one is somewhat improved over other models we've seen. Still, don't let the branding fool you, these are not headphone variants of studio monitors. Not even close.What does this response mean for you? Well, in addition to feeling like you have a subwoofer inside your head, you'll also notice that sibilants (s, sh sounds), cymbal crashes and high-hats will all sound a little muffled in comparison to other instruments and voice sounds. Given that these specific sounds are typically pretty loud in comparison to others when their levels aren't toned down a bit in an unmixed track, it's not terribly surprising that Audio Technica would elect to downplay these sounds. We still believe that if the track is mixed correctly, this underemphasis is unnecessary (and leads to bad mixing if you use these headphones at home to create tracks). These are not ideal headphones for this purpose.
Sennheiser HD 558 :
If you're looking for a flat frequency response, the Sennheiser HD 558 have a good one. What isn't pictured here, is a dropoff of about 10dB at 90Hz, meaning that these headphones may not be the best bet for bass-lovers, but will do fantastically well for most everyone else.
IT IS CLEAR FROM BOTH THE FR GRAPH AND THE REVIEW THAT THE M50 ARE INDEED "BASS-BOOSTED" PERIOD.
Now if the OP is looking for Bass-Neutral Headphones(as he mentioned in his first post) ATH M50 is obviously not the way to go, I have the Sennheiser HD 558 and I am satisfied by the amount of Bass it delivers despite the flat response it on paper.