I've just bought these headphones, and for about $50 I'm quite impressed with the value for money.
After listening for about 24 hours I've run them through some sine sweeps. Firstly, in the music I found the higher end of the bass is abit peaky resulting in some boominess and too much inferior quality bass in some tracks. Also, the highs on some tracks are a bit too harsh and loud. I also found the fit was a bit painful against my ears after wearing for a long time because the hard plastic under the stock pads would be touching my eartips.
Running through the sine sweep I found some significant peaks around 11khz and around 80-125Hz.
The mods I did address all of these issues:
Firstly we notice 3 holes or "ports" from the baffle area behind the driver (thanks for the picture, hope you don't mind me borrowing it):
I believe these holes act to use phasing to "boost" the bass ie The negative phase bass coming from teh other side of the driver (away from the ear) is pointed back in towards the ear in line with the phasing coming from the front of the driver. This is a typical trick used in a lot of large speaker systems... porting allowing sound pressure to come out of the enclosure. It tends to muddy up the bass for greater power. It can often be worth it in some cases, and if well engineered, can even be used to make speakers more accurate. In this case, I think it appeal to the type of crowd that just like bass, without being true connosiuers.
I sealed these "ports" up with glue tack. This cleaned up the bass significantly. Sine sweeps show more even bass. Tested it on music too, and it was succesful. If you still want a bit of power in your bass, I would suggest sealing up only 2 holes, and leaving one open. This might give best of both worlds.
For the hard plastic rubbing against the ear + the harsh highs, I simply grabbed 2 cotton rolls per earcup. I spread them out evenly (ie joined them together and then thinned them out) behind the foam pads: Between the driver and foam pads. This is another audio trick used to dull down speakers with high peaks in the "highs of the high frequency" (think of speakers with very thick felt covers). The higher the frequency of sound, the more it dulls. Hence, it's perfect for these headphones because they seem to me to peak around 11,000Khz: quite high in the treble range. This trick also helps to soften the plastic rubbing against my ears! Again, I think this was a feature left in place to appeal to less connosiuerial tastes. Bright sharp highs do have an instant appeal, but can get very annoying and wearying if you truly appreciate audio.
I spent a few hours trying diferent combinations. I found putting a reasonable layer of blutack on the baffle around the speakers helped a bit too, but it's already been tried here. This gluetack should help aborb the increased resonance from the increased build up of pressure resulting from sealing the driver baffle/enclosure off completely. This is mostly noticable at high volumes.
Hope it helps you guys!