Well, chiming in with some impressions and feedback. Fwiw I'm an early 30s male who listens to a lot of progressive metal (opeth, Mastodon, gojira, etc.). I'm driving them out of a humble MacBook pro/zte axon 7 into a fiio a5.
Stock, comfort is ok. Pads are not great, fairly scratchy, clamp is aggressive, but the headband is good. Bass is solid, mids are recessed/withdrawn, highs are a touch bright or peaky. Accurate and crisp. Soundstage is good, not enormous. Fast, they're fast and detailed. Didn't wow me if I'm honest, but kept with them.
After some days of use, mids come forward a hair, highs ease up some. This could just be getting used to them. Comfort improves as clamp eases. Engaging but a bit fatiguing at times.
With the back grills removed, highs become more open/airy? They also become more pleasant. Not a huge change, but noticeably better and enough to make replacement grills.
Vs hd600 at this stage, hd600 has very forward mids by comparison. Like, "holy crap that's a lotta mids." Bass on the senns is ok but no sub bass, like at all. Highs are recessed/quiet. All in all easier to listen to but not engaging. I sent the senns back.
Senns were better for poorly mixed tracks and doom/black metal. He4xx were better for good mixes, prog metal, Diana krall, Sting's Last Ship.
He4xx continues to warm up a bit over time, get used to the highs and either mids come forward or I get used to them being withdrawn.
Pad time: zmf Ori lambskin. Holy crap these are comfy. Cushy smoothness on your ears. Also, replacing pads is difficult. Very frustrating. HOURS of fighting, maybe I just suck. [
Edit: Turns out after I unscrewed the driver I screwed it back in too tightly. This caused a rattle but also made pad replacement a pain in the ass as there wasn't enough gap.] I got a good deal on lightly used lambskin, otherwise would have gone perforated.
Sound with pads: initially stalled due to clicking when compressed on left side. Turns out the air is funneling out the diaphram due to the seal,forcing the driver film back and it's clicking against the magnets. I followed this guide and resolved it:
https://m.imgur.com/gallery/ZXc05
Sound with pads fixed: mids! There they are! Seriously it seems like a very noticeable difference (more forward) compared to stock. I'd say a full step more prominent though not as shouty as the Sennheiser hd600. Sub bass is bumped up a half step. Treble is diminished a half step and is smoother/less fatiguing. All in all a more warm and relaxed sound, less fatiguing/sharp. Still detailed/fast, still engaging, no major changes in can pick out in soundstage, but I'm not listening to classical or anything. Might require a bit more power to drive, or maybe that's just the highs easing up and I can listen louder.
All in all I'm quite happy I kept these. Some tips:
- If you make your own grills, be careful of metal filings. You don't wanna have little magnetic shards in the drivers. I sanded mine down on the edges. I used an office Depot paper sorter ($6).
- Pads: probably best served with something perforated or hybrid to avoid the compression tunnel issue, otherwise use spacers to let air out per https://m.imgur.com/gallery/ZXc05
- My little amp improves the sound vs phone/Mac. Bass is fuller, sound is a a bit more punchy, treble is less grainy. If you're strapped for cash, they're still enjoyable without one imo. Fiio a5 gets these plenty loud for my setup on low gain.
- Edit: If you opt to unscrew the driver from the cup, say to add some sealer, or because you're stupid like me, do not screw it back in tightly. You want it as loose as possible while the metal ring doesn't move about. Screwing in too tightly makes it such that you can't get pads in, and it rattles.
Final form photo: