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...