I think if that is how you define it, then most mid-fi cans have sub-bass. Of course this is all relative to 1kz. You could show 40Hz on name that headphone but 40 to 60db down?
I define sub-bass as at least 40Hz and below and not that far down relative to 1kz. This would include orchestral bass drum, pipe organ, contra bassoon and tuba. The planars can do it, the expensive Stax can do it, some of the older Denons (5000,7000) can. IMHO.
many mid-fi cans have some sub bass.
the way i look at it is there's no definitive frequency range. One of the mastering techniques I use is if a source recording utilizes the sub bass region, I will slightly boost the recording at 30hz which is where the real core of sub bass frequencies are. A large amount of recordings don't have this frequency region. When I implement a low-pass, I notice there is a real area of transition from undefinable notes to definable frequencies in the 40hz-50hz. i got into an argument with an engineer quite recently who swears that for him sub bass dies out at precisely 59hz... go figure
Reads like you're using equalization to bring sub-bass to phones that don't have much. Of course that's legal. I'm too old school for that so I'm looking for a can that gives me reasonably accurate orchestral bass drum in Mahler symphonies without the boostaroo business.