As the frequency response shows, as well as previous Hifiman 400 cans, these headphone will have NO bass. Having owned the 400S with leather pad upgrade, bass got better but was still non-existent. It did sound very smooth and warm but bass was severely lacking. Also don't be fooled by them being open back. They have no soundstage whatsoever. You will have more soundstage in most decent closed back cans than you will with this. It will give you an intimate sound which is sometimes nice and many times not. Not good for gaming. Look at the Fidelio X2 if you want a headphone with bass and soundstage but won't sound nearly as smooth and warm.
BigTerminatorAs an owner of the he400 (og), which has a similar frequency curve, Im not overly comcerned with a lack of bass with these cans. If you listen to bass tracks from 90s car audio competitions, maybe you might be disappointed with the 30hz performance, but other than that?
Bass extension below 40hz drops off, but as these are nearly identical to the 400s freq response (see SBAF review), Im not too concerned.
SatsugaiThe original HE400 has the most bass out of any HE400x out there so what you are experiencing is completely different than what people with the newer models are. Take a look at the frequency response of your cans here: https://www.innerfidelity.com/images/HiFiMANHE400.pdf You have flat bass to 30Hz with minimal roll off to 20Hz. Now compare that to the graph for this headphone. Bass below even 30Hz makes a big difference as when I upgraded my subwoofer, the extra depth was noticeable, and that includes metal which is not very bass heavy. Bass is important, especially when you are used to speaker system that will always demolish headphones. These cans are extremely bass light which sucks.
BigTerminatorA subwoofer makes a difference in a home setup because many speakers lack proper bass extension and output. It is a fact that a small percentage of music goes below 30 hz. Most speakers do not offer requency response to 30 hz.
CujobobMost floor standing speakers lack the proper amount of bass extension and output to truly reproduce bass. You are right that most music do not got below 30hz, but if I were to apply an aggressive high pass filter at 20hz and one at 30hz you would be able to tell even with music having bass centered at 50hz. Bass notes have enough bandwidth to make mid bass have some sub bass extension. Also remember, flat 20hz bass to a microphone is not flat to our ears. Bass from 30hz has to be at least 3db higher than 80hz for it to sound flat to our ears. And 80hz should be 6db higher than 300hz. So even if a speaker can reach 30hz, it has to do so with much more output compared to the rest of the frequency range. It makes a difference plain and simple if you have the equipment to exploit it.