Apple - What is the impedance of the line/headphone jack on MacBook Pro Retina?

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: < 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): < -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.

The thing is, the higher impedance headphones will be much lower quality on a low impedance output such as the MacBook. Coming from an audiophile, if you only have a MacBook and you don't have the dough to buy a $500 headphone amp, it's not worth it! A $150 set of headphones would have better quality than an $800 dollar set without an amp.

I have a pair of Beyerdynamic 990 PRO 250 Ohm which supposedly use the same drivers as the 770 Pro 250 Ohm. I use these with a MacBook Air (early 2011) and have no trouble driving them at levels beyond what I would think of as comfortable or even healthy (but others may have a different definition of "loud").

On the positive side, if the output impedance of the MacBook is rated at <24 Ohm, then the 250 Ohm input impedance of the Beyerdynamics gives you a damping factor above 10 which helps keep distortion low.

Beyerdynamic have versions with lower impedance to deliver higher volume with portable equipment but I have found that even my Samsung Galaxy Note drives the 250 Ohm versions loud enough for my (almost 40 year old) ears.