Headphone Recommendations for Commuting

There are different degrees of closed if you analyse various headphone designs. Some are completely sealed at both front and back. Some have a closed back with earpads that let sound through and some are open back with open earpads that let sound in/out both sides. You can put sealed pads on an open back too, if you want to adversely affect its sound with no improvement to isolation. Put 540II open velvet pads on the HD250 and surprise surprise, it sounds pretty much like the 540II.

If your ER4 is in good working order, I would stick with it as you probably won't get the maximum potential out of full-size headphones on the go but would have to put up with their disadvantages and increased risk of damage/theft. The newest ER4 models are going to be incremental improvements of SQ at best, in my own judgement without hearing them. This is coming from someone who once owned about 16 different HD540 headphones and at least 6 different HD250 headphones. If quality control was already good then sound consistency between models of roughly the same type and design should be good and certainly comparable so save your money and buy more music with it instead.

2k+ for an in-ear device is a bit absurd. I would expect cutting-edge reproduction for that price and I really don't think that is achievable with in-ear devices.

Supporting Ash's experience on all those headphones the HD250's are very good. I mainly use my HD250 linear II's to edit soundfiles and sometimes for recordings. I have not tried them on trains but the sound isolation is pretty good so why not. Ash is spot on with the clarity and neutral timbre, which is why Graham recommended them to us as I recall. Moreover Ash's advice on refurbishing the Senns is based on his hands-on expertise and I've seen the great results of his approach to this.