I did not come up with the original idea, but it was lacking a proper instructable.
I recently bought a new soundcard and while the sound output was superb, I found the headset itself was lacking some bass.
stumbling the web I found that there were some users that modded the casing of the drivers with a couple of holes which would greatly add to the bass from the headphone.
At first I didn't believe it, but because I could always close up the holes again I decided to give it a shot.
The reason it works is because the PC350 is a closed system, adding the two holes allows the air to flow more, adding more bass response. This is however at the cost of fidelity. Which is the reason I decided to close mine back up.
Maybe I originally made the holes too big, I will address the sizing in the instructable itself.
**NOTE: opening up your headphones voids your warranty, if you do not want this then this instructable is not for you**