Sidebar 3: Measurements
It is difficult to make a meaningful measurement of a headphone's frequency response, not least because a flat response is not actually what is required. However, I did measure how the K 701's impedance changes with frequency (fig.1), as that gives an indication of how hard the headphones will be for the amplifier to drive. The AKG's impedance ranges between 60 and 65 ohms across most of the audioband, with a low electrical phase angle. The angle starts to increase above the low treble, but so does the impedance, due to the voice-coil inductance. This increase will therefore be benign. The AKG will be a little harder to drive than, say, the 200 ohms of a typical Sennheiser design, but easier than the 30 ohms of a Grado. There should be no problems with good headphone amplifiers.—John Atkinson
Fig.1 AKG K 701, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
Fig.1 AKG K 701, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
