[Ham Sandwich]

 
Quote:

most of the grado models have impedance value of 32ohm (pretty low) and sensetivity value of 98db which is also considered very low in the headphone world.   so what is the logic about them being very easy to drive? 

One reason for the Grado reputation of being easy to drive is that the sound doesn't change that much between unamped (iPod) and amped (a reasonable head-fi level amp).  At least with my SR60 the unamped and amped sound is very similar.  Higher end Grados may be different about that though.  I don't have enough experience with higher end Grados to know.  I just recently got my SR325is and haven't even bothered to try it straight from the iPod yet.  I've never even heard an RS1 yet.
 
I sometimes use my SR60 with the iPod.  But it's a drain on the battery.  Usually I use my Senn PX100 with the iPod.  The PX100 is much more efficient than the Grado and less of a drain on the battery.

 

[Head Injury]

Quote:

i wonder what wearing hd800's backwards does????

Makes them sound fantabulous out of an iPod Shuffle.

 

[GarageBoy]

Low impedence headphones will force the output to supply more current (i.e. it's closer to being a short)
That's why on amps, you get 400W at 8ohms, 800W at 4ohms
Problem is when the amp can't handle the high currents

 

[xnor]

Quote:

i think part of the problem with the k701/k702 may be the stock cabling design holding it back. 
[...]
does anyone else agree w/ me on this?

Nope I don't agree on that either. It's the driver construction, period.

 
Quote:

So low impedance headphones drain more battery life or high ones do?

Impedance alone doesn't tell you everything as I described in a previous post.

 
 
Back to what Ra97oR said:
Quote:

You may not have driven it correctly/properly but it may just not sound as bad as an underamped high impedance phone.

I thought about that and I came to the conclusion that this is wrong, at least (or especially) for portable devices.
 
The voltage of a portable device is limited, yes. But with <100% volume it's very likely not to produce distortion with a high impedance load connected.
Low impedance loads on the other hand can be a big problem. We've seen that with certain ipod etc. measurements that quite a few devices have problems powering low impedance (like 16 ohm) head/earphones correctly. Often the resut is rolled off bass response and other FR variations, distortion and so on.
To make things worse, some IEMs have impedance dips that go down to 10 ohm.
 
With headphones you don't have such problems, especially not if their impedance is higher.