Output Impedance

Bill-P said: ↑ The HD6xx series headphones have nominal impedance of 300 ohm plus a swing up to around 500 ohm at certain lower frequencies.



The HD700 has its nominal impedance around 150-200 ohm, and even though it also swings up in impedance, the peak is only around 350 ohm. If I know my math well, I'd say the HD600/650/580 is up to TWICE as hard to drive as the HD700. Click to expand...

Bill-P said: ↑ In general, I think most amps that sound good with low impedance headphones will typically not sound good with high impedance headphones, and vice versa. High impedance headphones are designed with such high impedance because they expect the source device (amplifier) to have a certain characteristic (output impedance, maybe?) that makes them not suitable for low impedance headphones to begin with. Click to expand...

Voltage Output vs. Current Output Amplifiers

Apogee Groove

"The sonic signature of the HD650 is also dependent of the output resistance of the used amplifier." (Solderdude, 13 (displaying HD650 frequency response measurements with both 10-ohm and 120-ohm output resistance) and (concluding that "[if] you want slightly (about 1dB) more bass/warmth in the HD650 use it from a high output R amplifier")). The higher the output impedance, the larger the bump in bass response.Solderdude discusses the differences between voltage output amplifiers and current output amplifiers. (Solderdude, 52) In the HD650's case, he concludes that a current output amplifier "would be great for increasing the speed of the driver, but the substantial rise in the impedance in the 100Hz area will also be 'lifted' in amplitude. (Ibid., (displaying HD650 impedance plot));"Measurements—Inner|Fidelity" above. "The impedance rises about 60% so the bass will be lifted about 4dB. The impedance rise above 7kHz is caused by the voice-coil inductance. At 20kHz the impedance is just 12% higher so just +1dB." (Solderdude, 52 (concluding that "[a] current drive amplifier thus is not well suited for the HD650 unless you want the headphone to become much more bassy"));ibid., 12–13 (discussing current source amplification))."The reality is you just need enough VOLTAGE when you want to drive the HD650 loud and nice."at 16.On April 5, 2016, Sennheiser announced its "perfect partnership" with Apogee and the release of a new bundle of the HD650 with the Apogee Groove USB DAC/amp which uses Contant Current Drive™ technology ( press release ). I have posted about my skepticism of this "perfect" pairing on Head-Fi . It is a decent option for a dongle, but the headphones deserve better.