Hi Everyone
I can offer my thoughts.
Firstly I need to confess I'm a bit more into headphones than a 'normal' person. Don't know why but I think because I use them so much - more than any other product in my life really - and I also love good sound. I am a professional video producer so I work with sound often.
My current selection of cans is as follows:
Sennheiser HD280 Pros (x2)
Shure SRH-840
ShureSRH-940
AKG 512 MK2
Logitech H800
Last week my Shure 840s broke in 2, randomly, for no reason. I was putting them on - suddenly the left earcup is just not part of the rest - a totally clean break just above the coupling where it joins the headband. Not happy at all. These have only ever been used at home and treated like the prized possession that they are (were).
That said, I have yet to hear a pair of headphones that even come close to the 840s - they are simply stunning soundwise - especially the clarity and punch of the bass, but the detail is also striking and they sound surprisingly light, airy and open.
So to cheer myself up a bit and to make sense of the whole situation I bought a pair of SRH 940s (Shure refuse to fix the 840s under warranty as they are over 2 years old - which is very poor as this product failed, not wear and tear, it was clearly faulty, they want £80 to repair them).
So I have to tell you, the 940s don't sound as good at all to my ears. Bass is lighter, and they are harsh in the treble, I honestly can't listen for too long as they are just not that enjoyable. The 840s you just can't listen to enough - I bought them having almost missed a flight once because I could not stop playing '1 more track' in duty free!
So I'm actually quite surprised, the 940s are revealing but in a 'too much treble' kind of a way. Bass is just not as solid - it's just like a Jackhammer on the 840s and although clear, it just has less oomph on the 940s.
It could be the 940s are better for mixing, it could be the 840s are a bit more bassy than they should be, but seriously, get the 840s and spend the rest on the Logitech bluetooth cans for the bus - they sound pretty good for what they are. Be warned the 840s have an itchy headband pad - but for the sound it's worth it! The 940s are way more comfy but frankly who cares!
I would still take the Sennheisers as my work-horses though as they sound very good (more listenable than the 940s) but they can be worn for a whole day without getting uncomfortable.
By the way - I have done a proper 'pepsi challenge' to write this, when I hold the 'dangling by its wire' left cup over my left ear the 840s still sound better than the 940s, more open, fuller but super-crisp base, astounding detail (you seriously catch yourself turning around because you think you heard something in the room - then you realise it was in the room the recording was made in - really - it happens to me often).
Also, separation better on 840s, and vocals sweeter (used Burn by Ellie Goulding for that - the beginning is a clean vocal and a well-produced one at that).
I will update after the 940s have 'broken in' but then I don't really believe in all that - the 840s rocked my world on day1.
Let's face it - I'm gutted.
Hope this helps.