[Chris J]

  Actually the HD800 (102 dB/mw) is more sensitive than the HD600 (97 dB/mw) or HD650 (98 dB/mw).

 
More efficient.
The HD800 is more efficient. 
The numbers you have quoted relate power to SPL, this is properly called efficiency.
 
You can't properly relate these number to each other without referring to the impedance of the 'phones.
 
Sensitivity is actually a number that expresses how much VOLTAGE a headphone takes to reach a specific SPL.

 

[Chris J]

  And the actual reason is?
The FiiO E12:
15.5 Vp-p
Rated for 300 Ohms
> 16 db Gain
Output impedance <0.5Ω
THD <0.005%
 
If it can hurt your ears using an HD600, the HD800 is even more sensitive and will play even louder. It cannot drive a low impedance low efficiency Planar Magnetic can, however, not many amps can - including many very expensive ones.

 
OK, that wasn't to be taken very seriously.
In my opinion, I would not drive a pair of $1400 phones with a $125 amp.
If it was my money, I would be more inclined to spend maybe half on the amp, half on the 'phones.
 
Just my opinion, but the E12 doesn't sound as good as a Matrix M Stage (for example). 
Obviously, if it's your money, you can spend it any way you want!

 

[miceblue]

What the heck does "drive" even mean for a headphone?

X amp with Y headphone sounds really good since X properly "parks" the headphone and really makes it "shine" with great "PRaT" and it sounds very "musical."

 

[Chris J]

  FiiO has a max power output of 160mW to drive 300ohm cans whereas HD800 allow max. input power of 500 mW.which is of 300% more than FiiO's ability to drive 300ohms. So looks like, E12 can drive hd800 good BUT NOT THAT GOOD. Also the hd800's driver dia 56mm has more voice coil windings.

 
I don't see why you need 500 mW to drive a pair of HD800............unless you want to go really, really deaf! 
And not too sure where the 56 mm driver makes any difference as to whether 160 mW or 500 mW is "enough"?

 

 

[StanD]

   
More efficient.
The HD800 is more efficient. 
The numbers you have quoted relate power to SPL, this is properly called efficiency.
 
You can't properly relate these number to each other without referring to the impedance of the 'phones.
 
Sensitivity is actually a number that expresses how much VOLTAGE a headphone takes to reach a specific SPL.

All of the cans I referred to are 300 Ohms, the same impedance, thus these cans can be related to each other whether you are looking at Voltage or Power to SPL relationships.
 
Actually Power to SPL is called Sensitivity Rating by many, Crown included. I can see why many like to think in terms of voltage as amps deliver in those terms as long as they can handle the load impedance. As long as the number specifies V ro A, I can deal with it.
http://www.crownaudio.com/elect-pwr-req.htm

 

[StanD]

  FiiO has a max power output of 160mW to drive 300ohm cans whereas HD800 allow max. input power of 500 mW.which is of 300% more than FiiO's ability to drive 300ohms. So looks like, E12 can drive hd800 good BUT NOT THAT GOOD. Also the hd800's driver dia 56mm has more voice coil windings.

Max. input power is where you damage the cans. Trust me, your ears will hurt well before that happens, something to be avoided. The HD800's are louder than the HD600's at the same level of amplification. The number of windings has nothing to do with it.

 

[Chris J]

  All of the cans I referred to are 300 Ohms, the same impedance, thus these cans can be related to each other whether you are looking at Voltage or Power to SPL relationships.
 
Actually Power to SPL is called Sensitivity Rating by many, Crown included. I can see why many like to think in terms of voltage as amps deliver in those terms as long as they can handle the load impedance. As long as the number specifies V ro A, I can deal with it.
http://www.crownaudio.com/elect-pwr-req.htm

 
That's just confusing. Maybe you "can deal with it", but it just adds to the general confusion of all things headphone.
 
http://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sensitivity
 
Sensitivity in loudspeakers often refers to 2.83 Volts applied to loudspeaker.

 

[StanD]

   
That's just confusing. Maybe you "can deal with it", but it just adds to the general confusion of all things headphone.
 
http://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sensitivity
 
Sensitivity in loudspeakers often refers to 2.83 Volts applied to loudspeaker.

The math and formulae are not such a big deal. No calculus yet - lol. IMO most confusion comes from loosely defined terms that we use to describe what we are hearing. One guy's warm is something else to the next person.

 

[Evshrug]

^
I don't even like the term "warm".

 

[Chris J]

  The math and formulae are not such a big deal. No calculus yet - lol. IMO most confusion comes from loosely defined terms that we use to describe what we are hearing. One guy's warm is something else to the next person.

 
My real take on this is:
There are a lot of Head Fi-ers who just want to buy an amp for their 'phones, and want to know what works without using any math.
 
The sensitivity thing amused me: how much SPL do we get at 1 Watt?  But Wait! It's really referenced to 2.83 Volts into 8 Ohms! So it's really how much SPL do we get from 2.83 Volts driving a "nominally" 8 Ohm speaker. As you obviously know, is an 8 Ohm speaker really 8 Ohms? So let's standardize it and use a 2.83 Volt signal to the loudspeaker. 
 
Obviously headphones are a pain in the butt compared to speakers.  You can assume almost any loudspeaker is 8 Ohms and not get into too much trouble when shopping for an appropriate amp.
You can see that a lot of people get confused by the impedance and sensitivity and efficiency and voltage gain and how much amplifier do I need to make my headphones go?  

 
As for loosely defined terms, try asking 10 Head Fi-ers which 'phone is brighter, the Q701 or the DT880s.................you may get 10 different variations on an opinion!  

 

 

[Chris J]

^
I don't even like the term "warm".

How about "cuddly"?

 

[StanD]

   
My real take on this is:
There are a lot of Head Fi-ers who just want to buy an amp for their 'phones, and want to know what works without using any math.
 
The sensitivity thing amused me: how much SPL do we get at 1 Watt?  But Wait! It's really referenced to 2.83 Volts into 8 Ohms! So it's really how much SPL do we get from 2.83 Volts driving a "nominally" 8 Ohm speaker. As you obviously know, is an 8 Ohm speaker really 8 Ohms? So let's standardize it and use a 2.83 Volt signal to the loudspeaker. 
 
Obviously headphones are a pain in the butt compared to speakers.  You can assume almost any loudspeaker is 8 Ohms and not get into too much trouble when shopping for an appropriate amp.
You can see that a lot of people get confused by the impedance and sensitivity and efficiency and voltage gain and how much amplifier do I need to make my headphones go?  

 
As for loosely defined terms, try asking 10 Head Fi-ers which 'phone is brighter, the Q701 or the DT880s.................you may get 10 different variations on an opinion!  

 

Not all speakers are 8 Ohms, most are but the one time you get it wrong can be oogly. I always thought that 10 Head-Fiers would give you at least 20 answers plus numerous revisions.

 

[StanD]

  How about "cuddly"?

That explains your Avatar.
Can a HP be warm and fuzzy at the same time?

 

[Chris J]

  That explains your Avatar.
Can a HP be warm and fuzzy at the same time?

 
My Beyer DT880 are warmer sounding than my Q701.  (in my opinion! subject to revision!)
The ear pads are quite fuzzy, so I consider them the warm and fuzzy headphone. (in my opinion! subject to revision!)
 
My Avatar is explained in my personal profile as is my opinion on Monica Bellucci.

 

[GWagon]

This may be a dumb question but do the batteries in amps drain when the amp is left on with no music playing through it?