What is the impedance of the line/headphone jack on MacBook Pro Retina? I want to buy headphones that I will primarily use on my MacBook Pro Retina. I read that I should not buy headphones with high impedance because the volume will be really low. I want something I can use with my MacBook and my iPad. I looked at these headphones, but I'm afraid they will not work well for my purposes:

http://www.amazon.com/Beyerdynamic-770-PRO-250-ohms/dp/B0006NL5SM/ref=pd_cp_e_0

Does anyone have experience with this stuff?
I couldn't find the specific details for the new MacBook Pro Retina machine, but these specs are pretty universal across the whole MBP lineup and should help you match a pair of headphones:


  Line/Headphone Output
  
  The line/headphone output is automatically selected for audio output if no external device is detected at the S/PDIF optical digital output port. The line/headphone output supports a stereo data stream at bit depths of 16, 20, or 24 bits per sample and at sample rates of 44.1 kHz, 48 kHz, or 96 kHz. The line/headphone output volume can be adjusted from 0.0 dB to -95.25 dB.
  
  During playback of a 1 kHz, full-scale sine wave (44.1 kHz output sample rate, 24-bit sample depth, 100 kΩ load, unless otherwise specified) the audio line output has the following nominal specifications:
  
  Jack type: 3.5 mm stereo
  Maximum output voltage: 2 VRMS (+8.24 dBu)
  Output impedance: &lt; 24 Ω
  Frequency response: 20 Hz to 20 kHz, +0.5 dB/-3 dB
  Signal-to-noise ratio (SNR): > 90 dB
  Total harmonic distortion + noise (THD+N): &lt; -80 dB (0.01%)
  Channel separation: > 75 dB
  
  Note: For best results, equipment plugged into the line/headphone output jack should not connect the audio ground to other grounds, such as the chassis or “green-wire” ground.


The answer to that post doesn't contain a reference link I'm afraid.

I did find a link on the Apple Support page that says the Mac Mini's headphone jack is 10 Ohms.

All this is to say: yes, you're correct. Those headphones are far too high a load for the limited-power amplifiers in your iDevices and your MacBook Pro.

You want a lower impedance headphones. They're more efficient at converting the electrical signal they're passed in to sound you can hear. More efficient means, for the same power electrical signal, higher volume reproduction.

Aim for something the less-than-or-equal to 64 Ohm range if you can.