Nothing is more tedious than some headphone "audiophile" who begs you not to buy these ear pads because he insists they aren't worth your time and money simply because he doesn't like how they sound. I purchased a pair about a year ago, and I love how smooth, open, and uncolored the sound is. Oh, wait! These earpads have no sound characteristics. It must be the actual drivers that create the sound! For the record, I still thoroughly enjoy my HD 650 headphones from both balanced and single-ended sound sources with these earpads. My point is to buy whatever you want and avoid letting these reviews influence your buying decisions by begging you not to buy for some nebulous reason they think is essential.

Although these pads do in fact reduce the detail in mid and upper-mids on my HD6XX, they really shine at being incredibly comfortable/well manufactured pads and bring out the excellent sub-bass that these headphones are capable of, even though they're really regarded as the de facto "well-balanced with intimate and detailed mids" option, with stock pads. I honestly think these bring some excitement to the headphone without turning into a muddy experience; soundstage and separation doesn't seem to be impacted to my ears at least. I'm running them with a JDS Labs Atom Amp and DAC stack, which really helps drive the transparency and detail.

Kick drums, toms, and guitars to me just sound more full to me when compared with the stock pads, which I think is due to the tight stitching along with the noticeable bass and sub-bass. Male vocals too. I listen to a lot of post-hardcore/metalcore/blues and alt-bands that sound like the Silversun Pickups.

If you're considering these for HD6XX or HD650's, just know what you're getting into. I'm really happy with the change in sound presentation when compared to the stock pads, and what's presented is actually a great tune for gaming since you still get impressive detail, separation and soundstage at the cost of a reduction in detail in the mids. The mids end up sounding fine to me (especially lower-mids, they sound a bit more full) but I think it comes down to preference. And if you're a HD600 owner check out DMS' thoughts on a pad swap video with Dekoni on Youtube.

PLEASE - for your own time - do NOT buy these! If you're like me, the worst thing about your HD650s are the intimate soundstage. I bought these thicker ear pads thinking they would at least help in this regard while feeling and looking much more premium than the seemingly cheap ones that come stock. NOPE! Maybe the soundstage was slightly improved, but wow were the mids just destroyed. I LOVE mids, so I enjoy the Sennheiser sound signature and these pads just make it so bad. It's like a bad bass booster- the bass becomes over-powering and sloppy while all the detail comes off the now-recessed mids and the highs. It took two songs for me to go back to the original pads with a whole new appreciation! They may look and feel cheap and awful, but they MAKE this headphone.
Please please please don't waste your time and money and hassle (and Sweetwater's time and money and hassle) on these pads and accept that your stock pads are as good as your Sennheisers are gonna get.