[hraza76]

What's the deal with high impedance headphones...If both Fidelio X2 and AKG Q701 are meant to be audiophile open back headphones, why X2 is much more suitable to work better with portable devices without requiring amp? Just wondering.  Also, Bayerdynamics has the DT880 in two version one low ohms and one higher...why?

 

[cel4145]

The amps in portable devices work well with lower impedance, higher sensitivity headphones. The Q701s are not very sensitive. Sensitivity is a measure of how much power (or voltage) a headphone needs.

 

[tx-sil]

You need to look at both impedance as well as sensitivity. low impedance + high sensitivity means easy to drive but less potential. AKG K701 is a special case. It requires high currency on output in order to be driven properly. High currency, as you can tell, may cause problem like potential damaging low impedance earphone and requires great power sources so most portable AMPS tend to not have such high currency design.For example, SMSL V2 is a very capable AMP and it can properly drive HD600 if not HD650, but multiple people have complained that K701 sounds terrible on V2, because it's output currency is not high enough. Hope this makes sense 

 

[PurpleAngel]

  What's the deal with high impedance headphones...If both Fidelio X2 and AKG Q701 are meant to be audiophile open back headphones, why X2 is much more suitable to work better with portable devices without requiring amp? Just wondering.  Also, Bayerdynamics has the DT880 in two version one low ohms and one higher...why?

 
I believe some of the AKGs and Beyerdynamics models are based on older designs, when your stereo receiver was more likely used to drive headphones.
Also I know (at least in the past), high impedance headphones was better suited for working with studio audio equipment.
Where as the Philips Fidelio is a newer design that I guesses was expected to be sold to people who own iPods or iPhones or smart phones, etc.
 
Usually the 600-Ohm version of a Beyerdynamic headphones (DT770/DT880/DT990) provides better audio quality, then the 250-Ohm version.
But the 250-Ohm version can work with more sources, then the 600-Ohm version.
I think Beyerdynamic come out with 32-Ohm versions (DT770/DT880/DT990) to make them work better with portable stuff (iPod, iPhone, smartphone, DAP, etc).