I've been listening to these since I received them this afternoon. I've listened to them through my phone only, through two different solid state amps, and a tube amp. I'm quite impressed with the bass response. It's a little muddy through solid state but mellows out a bit with tubes. Even with the slight muddy bass, the midrange is still typical Sennheiser. Clear and warm. That's where Sennheisers shine. The treble is nicely crisp but not too bright. I'm very impressed with the HD 559's and just think, they're not even broken in yet. I think with time the bass will settle down a bit. But there's nothing wrong with a little EQ in the meantime.
This was a present to someone in the family, who likes listening to music on the smart phone but so far has not invested much into listening gears. He listens to various kinds of music and says that the experience is perfectly OK for him. In my experience, better quality headphones often ruin the listening experience of not too high quality music (which can be a frustrating experience). A lot of people complain about this phone not being too strong in the treble region. This helps with lots of YouTube music which tend to be very sibilant on good headphones. So, to sum up: good choice for a casual listener who wants comfort and good listening experience with various genres and levels of recording quality.
update: the obvious downside: only one (3 metre) cable is provided, which has the quarter inch plug. So, after buying a shorter cable with the 3.5 mm plug and possibly the adaptor from 6.5 mm to 3.5 mm (which I did to make the present better usable), the price reaches the price of the 599 SE (Amazon) discounted price, which I ended up buying for myself and am perfectly satisfied with it as the standard headphones with my phone.
Luckily all our phones have a jack, (old Samsung, Redmi 8) Medium category phones are quite easy to find with a jack. My guess is that it would easily work with a modern USB-C to jack connectors as well. (Of course, one would need to test that to make sure.) And yes, it would look quite error prone using two adaptors at the end of the cable. (quarter inch to 3.5mm + the usb-c adaptor)
It's been a while since I've been able to get my hands on a pair of Sennheiser headphones, and over all I've missed the amazingly neutral sound profile.
Only Negatives I can give are the legnth of the cable, the pressure of the headband, the cheapish plastic build quality, and how it doesn't feel like it's sitting right on my head. But otherwise these are great headphones for the price.
Sennheiser is misleading people with the HD 599 product. Massdrop may not even know that the box says "UNLOCK YOUR HOME AUDIO'S TRUE POTENTIAL". So somebody will assume that it will be a great adventure. However, I opened the box and found no adapter to use on a smartphone or media computer? Usually there is a 1/4" male to 1/8" female so it can be used. There is only a 1/4" male connector. The other end is connected to the headphone. I checked the user guide and inside the guide it says, under heading "Intended use/Liability" that " The headphones are designed for use with portable devices and hi-fi systems." They are misleading people here! I did not complain to Massdrop ie. Drop because what can they do for me as I live outside USA.
A 3.5mm jack is industry standard these days. It should be expected. This ain't the 1980's or a $1500 pair of cans that requires a desktop amp. That's honestly kinda scummy of them. I shelled out for a custom cable on my HE4xx's because I really liked them, but they included a normal 3.5mm terminating cable with a 1/4 inch adapter.
This is my third product from Sennheiser and it really is a hit. My only complaints are that it does have a kinda creaky plastic feel, it's pretty clampy to start with, and the cable locking mechanism is a little weird. Now with that out of the way, the sound is special and unique. It has thumpin' bass and really great overall extension. The headband is the most comfortable in this series due to the amount of padding. 3d effect of sound is overall good and can give you good indications of where opponents are coming from in games. Also, they stay relatively cool compared to the monoprice classics.