So I saw that in the past, people talked about swapping the Teak cups onto the TH-900 or using TH-900 drivers. I always wanted to give it a shot and I was finally able to do so recently. I also got to compare the TH-900 driver vs E-MU driver since I had a spare pair of the Urushi cups and Teak pads.
I'll start off with the TH-900 vs E-MU. When comparing TH-900 stock vs E-MU Teaks stock, there was a very obvious difference in tonality and perceived resolution. The TH-900 traded off the warmth and intimacy of the Teaks for a larger soundstage and very resolving bass. Soundstage size wasn't AKG 700 or HD800 level, but still bigger than expected for a semi-closed pair. Imaging was also very good and more filled-in. The bass was incredibly clean and well-textured, I'd say very close to the quality you get with the LCD-XC 2021. It boggles my mind that the E-MU Teak's bass can sound "one-note" compared to these two headphones.
The treble on the TH-900 was certainly elevated more than the Teaks, but didn't bother me the way Beyerdynamic spikes do. I was expecting that kind of thin, metallic coloration that Beyers have, but the TH-900 didn't have as much of that, so that was a nice surprise.
Now, I say "perceived resolution" because the pads and the cups actually had a larger effect than I expected here. Once I "equalized" the headphones by having them use both Urushi cups and E-MU Teak pads, the difference in resolution was much harder to pick out. I still subjectively found that the TH-900 driver was a little bit cleaner, had more defined trailing ends and textures, and had better imaging. But when conducting informal blind A/B tests with the help of a friend, the results were inconclusive. We were able to differentiate them consistently on certain tracks, but not on others.
My reasoning is that E-MU Teak pads contribute a good deal to the warmth in the Teaks. They tame the treble and bump up the mid-bass. But this warmth does bloom a little into the mids and muddies up the bass a bit, making it harder to pick out the finer details in music even if the driver is capable of doing so. The Teak pads also have a smaller soundstage, so it's easier for the sounds to blend together.
So when I moved on and slapped the Teak cups and pads onto the TH-900, I was hoping it'd just be like a more resolving Teak. But it ended up sounding very similar to the stock E-MU Teak, just with a little more filled-in imaging. However, the difference in resolution did seem more noticeable when I used different pads like the TH-610 pads or the TH-900 pads. I can't say that with 100% confidence though since I don't have another pair of TH-900s to do comparisons with.
Eventually, I ended up going with the TH-900 Teaks and the TH-610 pads. While I felt the TH-610 pads made the E-MU Teaks sound too flat and boring, the TH-900 Teaks seem to fare better due to the extra resolution. But during these comparisons, I realized that there was an issue with the Teak cups that I hadn't quite nailed down before. While I still think the Teak cups have better mids in general than the Urushi cups, the Urushi cups sounded better specifically with
female vocals. The Teak cups made certain female vocals a little edgy, not quite what I'd call sibilant but enough to be annoying now that I identified it.
After some tinkering, I found out that the dampening in the Urushi cups smoothed out that edge in the female vocals. Tearing that off and sticking it in with the Teak cups got rid of that edginess, so that was a nice little discovery.
EDIT: In hindsight, perhaps this is also similar to how the TH-610 sounds since those also come with the TH-900 cup dampening.
In addition, with the dampening gone on the Urushi cups, they did end up sounding very similar to the Ebony cups as I expected, since they're cut in the same way. However, the Ebony cups still have the hardest hitting bass, the Urushi are in-between the Teaks and the Ebony in terms of slam.
Lastly, I also decided to give the
Fostex EZ mods a try. Unlike the TH-900, the foam rings on the E-MU are glued on, so I had to carefully peel that off. Fortunately, they don't really move on their own anyways, so this didn't really change anything. Subjectively, I did feel like the different foam positions did change the sound a bit, mainly in terms of soundstage presentation and bass impact. But like the driver differences, it's really hard to tell when using the Teak pads. And the overall change is still subtle, I'd say it's less impactful than cup changes or pad changes.
