I’m still fixated on comparing the S to the S2, haven’t yet plugged in any other cans to do A/B’s yet. I’m trying to answer the question, for myself, if the S2 is better than the original, and if I want to keep the S, S2 (or possibly both?)
I’m still an unabashed fan of the original 660S. Here are some more notes I’ve taken in the last 12 or so hours. Many of these differences amount to splitting hairs, and aren’t colossal differences by any stretch. I’m definitely beginning to see the appeal of the S2, and why it has so many proponents. But for me, I’m still a little bit leaning toward the OG side. I never thought that it really needed improvements, so any changes made to the S to make an S2 would have to be things that fall into the category of “I didn’t know I needed that!” I always thought that the S did so many things right, it is kind of perfect for what it is.
Resolution
I think the overall resolving power of the S2 is in fact a little better. Subtle details are highlighted that I can also hear on the S, but I hadn’t noticed on the first pass. I first hear them on the S2 and then go back and hunt for them on the S.
Bass
S bass is tighter, I can follow bass lines a little better, and I think the timbre of acoustic and electric bass guitars, as well as the lower range of acoustic guitars (nylon strings in particular) sounds better on the S. Bass depth sometimes sounds a little unnatural to me on S2, and distracts me often. Kick drums thump harder on the S2, and depending on the genre this could definitely be an improvement over S. I have a preference for clean mid-bass presentation, not usually a fan of a ~150 Hz hump (like 650). S2 has a little of this hump I think (also supported by graphs). S does not.
Treble
Definitely more sparkly on the S2. I like it more, but this (I think) is also the quality that’s making vocals sound a little distant and slightly more raspy/tizzy on the newer model. I think it’s giving the headphone a coolness, sonically speaking, that I think is less-good.
Vocal Quality
Vocal presentation has a touch more body on S, sounds more natural to me. S2 can sound a touch nasal wrt vocal quality, a little more zing. Some male vocals can sound a bit nasal sometimes, but it’s exaggerated on the S2, and sounds way more true-to-life on the S.
Imaging/Separation/Layering
S2 separation seems a touch better, imaging seems a smidge more precise. But there’s a slight bit of incoherence in the new model to my ears, like something’s off in the midrange. Again, it sounds “cooler” to me. Busy passages and poorer quality recordings seem to be handled better on the S2. They’re both pretty forgiving of crappy source material, but I think maybe the S2 is even more so. Good? Bad? You decide for yourself
Soundstage
Soundstage is definitely bigger (and TALLER) on the S2. It is less intimate (which could be a plus or a minus, depending). Depth of stage is improved on the S2, creating a more realistic perceived acoustic space. It’s more holographic to my ears. I think adding a touch of the HD800S’s spaciousness and detail was a goal of Sennheiser for this headphone, and it shows. I think it comes down to how much those traits mean to you in the spectrum of technicalities. For me, it’s not high on the list (soundstage width, I mean)
Dynamics
S2 is more dynamic. Snare hits are sometimes a little arresting in their immediacy. This is a huge plus for the S2, it’s more exciting.
I’m sure I’ll have more thoughts soon. And I’ll share them. In short, they’re pretty similar. Both are really solid headphones. I’m not convinced that the new flavor is better, just different. But I can definitely see why the newer model would appeal to others. I think the real bargain right now are all the 660S popping up in the classifieds for ~225 bucks. It’s like 98% the sound of the S2 for less than half the asking price.