Okay I've been using the 840 pads for a good 16 days and I can say without a doubt that there is a sound change. I could tell immediately when I changed the earpads because it has a similar effect to changing the EQ. Here I'll list some differences.
Sound with the stock M50 pads (Compared to a 2 week 840 listening experience)
- The sound stage is noticeably smaller; the highs (Acoustic Guitar) feel right next to your ear, maybe even louder.
- I can tell the mids are recessed because my ears are paying more attention to the highs than the vocals.
- Time to put on some electronic music :: Listened to LCD Soundsystem's "I'm Losing My Edge" first with M50 pads
- The bass is easily louder and more punchy. Feels soft now that I'm on the 840s
- The other sounds aren't as loud and in your face. (At the moment I'm attributing this to the fact that the pads make the drivers further away than stock pads
Verdict: With the soundstage being larger, a lot of the sounds are recessed but the mids do come forward; vocals are increased. The comfort level of the 840s is a huge improvement. Overall the M50 pad's sound is my favorite of the two. The sound is louder, clearer, closer. It doesn't give the sound much room to breathe but that's the way it was meant to be heard, as studio monitoring. I really wish these pads were more comfortable because I really just can't stand it after a few hours. I'm probably going to be switching these a lot more often, or I'm going to fork out some $$ to get the M50 replacement pads (more expensive than the 840 pads).
If I were to suggest anything, I'd say just re-buy the stock M50 pads if you're happy with the sound but not happy with how thinned the padding has gotten. If you want something really comfortable but wouldn't mind an EQ change, get the 840 pads. To me, comfort is overall the deciding factor. I listen for hours long and if the driver is touching my ear it's not good.
*Note: I think the fact that the driver is so close actually adds to the ear-hurting factor at loud volumes
*Wipe down your pads often; don't want them cracking.
I can do further analyzing if people want.