The holes definitely make a difference. I've tried the other Fostex earpads, which are basically the Teak pads but with larger ear holes. The smaller ear hole on the Teaks helps in reducing the treble and shifting the balance to something warmer and more "liquid" sounding. Also seems to contribute to the intimacy of the sound. The TH-610 pads lose that warmth and sounds more dry, while the TH-900 pads sound noticeably more open and spacious, but start getting too aggressive in the highs.I know, right?
Man I've tried a dozen freakin pads on these over the better part of the last six years - and I just have to come back to my stock ones for the sound eventually. I was b!tching just a month or so ago, I had ditched stock and put on Dekoni Elite Angled Velours (got those with an He-4XXs) and when I put back stock again, after months, man I started hating the other pads.
Besides those, I have tried Brainwavz Angled Sheepskin (radio sound, bad, lost bass), Brainwavz Regular Sheepskin (radio sound, bad, lost bass), Brainwavz Hybrid Velours (lost bass, highs increased), Fenestrated (AE Hifiman) Angled pads (lost bass impact - those now are great with my M1060cs), Sheepskin Angled (AE pads) (still losing bass there), Brainwavz XL Sheepskin (what a fail, that one), Hifiman Stock Pleather (lost bass, treble high), Beyerdynamic Velour Pads (nice pads, but smaller, and lost bass impact), Cheaper AE Pleather pads (too mushy, closer sound, but still lost bass impact somehow).
For the life of me, I can't find an alternative to stock pads. I have finally ordered these now: https://www.aliexpress.com/item/1005004161760873.html
If these can do 90% of what stock can, cuz maybe they'd be comfortable as it's going to be sheepskin. Anyhow, fingers crossed - will come back on these.
Something tells me, the smaller, uncomfortable holes may have to do with the most optimal sound delivery. Something also tells me that the actual attenuation rings GLUED INTO the stock pads may also have something to do with the sound. That's two attenuation rings on each side in stock form - I wonder if there's an actual play there. Also, the stock pads are just not sloppy and tight and firm - maybe that also plays a role with just the best bass impact delivery of all the pads I (or most other folks) have tried.
Let's see - will figure out things a lot better once I get my hands on these. Will surely post here with my findings - this crap is important. Bout time we put this dilemma aside for good.
The Accessory House sheepskin pads are very close to the dimensions of the stock Teak pads and also have attenuation rings, but they sounded a bit brighter than stock. So that makes me think the attenuation ring and perhaps the foam density they use also affect the sound.
Question though, you said there are two attenuation rings on each of the stock pads? That surprises me because I took apart the TH-900 pads and I only found one attenuation ring sewn in for each pad, so I assumed it'd be the same for the stock Teak pads.