That's what he said

"If u supply 150 ohm to the the headphone, other then lack of bass, the mid and high freq is clearly define. in fact it is one of the best gaming headset, if u try to drive with a ipod, well, it's crap."

Me: What happens if I supply 10kohm or 2 ohm to the headphone?

"for 10 kohm, the headphone will be gone.

for 2 ohm, if you are lucky, you can still hear some sounds with the volume at full.

Never use your speaker output to connect to yr headphone."

ragnarok95: Nice question to test someone.

"in fact a lot of people are not aware of it, got hole just plug.

Esp those high end headphone (300 and above), you need to match the ohm in order for it to performance.

From some of the reviews complaining PC350 is cmi, you can see that they just use 64 ohm to drive the headset (which need 150 ohm)."

Me: Okay final question, pardon me noob, you said can see others just use 64 ohm to drive the headset, while you know 150 ohm is good for the PC350, but how do you know how many ohm your soundcard is supplying to the headphone?

"u need a dac or a sound card come with a headphone amp to drive high ohm headphone.

for dac, there is a switch for u to adjust the gain, sound card is control by software."

He didn't answer my question, but that's enough from me.

Source:
http://forums.hardwarezone.com.sg/showthread.php?t=3097327&page=3