If I put my notes here, I might be able to find them again later!
Headphone Sensitivity: AKG K702 vs. Sennheiser HD 600
I recently obtained a pair of AKG K702 headphones to complement my long-standing reference Sennheiser HD 600s. I figured since I'm building headphone amplifiers it would be a good idea to have a reference grade low impedance model as well as the high impedance HD 600s to use for evaluation.
First though, a note on sensitivity:
K702: 62 ohms, 105 SPL/V
HD600: 300 ohms, 97 dB/mW
Different units. Grrr!
At the same volume position I quickly discovered the HD 600s play slightly louder than the K702s. The datasheet values predict the K702s should be about 3 dB louder, so it seems the sensitivity is off by as much as 6 dB.
In numbers,
K702: 62 ohms, 105 SPL/V ... 93 dB/mW from datasheet, 87~89 dB/mW (99~101 SPL/V) in practice.
HD 600: 300 ohms, 97 dB/mW ... 102 SPL/V.
The K702 requires as much as ten times more power to drive than the HD 600s. The voltage sensitivity is about 3 dB lower than the HD 600, which means that a headphone amp with even more gain is needed and the HD 600 already works best with amps in the 20~26 dB range...
Take home: true to the AKG heritage, the K702 are essentially "ear speakers". Unless your headphone amp has a high gain setting and loads of clean power on tap, my advice is to stay clear. My Nexus 7, for example, is incapable of driving them to a reasonable volume level. To put it in perspective, to achieve 110 dB on the AKG K702s requires 200 mW: 3.5 V and 56 mA rms ... 80 mA peak!
The same output level from the HD 600 needs 21 mW: 2.5 V and just 8 mA rms.
(At my usual listening level, I estimate the K702s require a maximum peak power of 20 mW, 25 mA peak current. That's just within the class A envelope of the Sapphire headphone amp I'm using, but well beyond the datasheet output power of most mobile devices.)
First though, a note on sensitivity:
K702: 62 ohms, 105 SPL/V
HD600: 300 ohms, 97 dB/mW
Different units. Grrr!
At the same volume position I quickly discovered the HD 600s play slightly louder than the K702s. The datasheet values predict the K702s should be about 3 dB louder, so it seems the sensitivity is off by as much as 6 dB.
In numbers,
K702: 62 ohms, 105 SPL/V ... 93 dB/mW from datasheet, 87~89 dB/mW (99~101 SPL/V) in practice.
HD 600: 300 ohms, 97 dB/mW ... 102 SPL/V.
The K702 requires as much as ten times more power to drive than the HD 600s. The voltage sensitivity is about 3 dB lower than the HD 600, which means that a headphone amp with even more gain is needed and the HD 600 already works best with amps in the 20~26 dB range...
Take home: true to the AKG heritage, the K702 are essentially "ear speakers". Unless your headphone amp has a high gain setting and loads of clean power on tap, my advice is to stay clear. My Nexus 7, for example, is incapable of driving them to a reasonable volume level. To put it in perspective, to achieve 110 dB on the AKG K702s requires 200 mW: 3.5 V and 56 mA rms ... 80 mA peak!
The same output level from the HD 600 needs 21 mW: 2.5 V and just 8 mA rms.(At my usual listening level, I estimate the K702s require a maximum peak power of 20 mW, 25 mA peak current. That's just within the class A envelope of the Sapphire headphone amp I'm using, but well beyond the datasheet output power of most mobile devices.)
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