Headphone Reviews

As Jim Austin explains, electrical impedance of headphones is a matter much misunderstood—even among reviewers, who, you would think, should know better. (The Internet has brought forth an entire community of reviewers who seem ignorant of the basics of audio engineering.) I examined the Grado SR60i's electrical impedance (fig.1) with my Audio Precision System One and the headphones sitting against my ears. The SR60i has a minimum impedance of 32 ohms, as specified. A broad rise evident in the midbass and centered at 75Hz is presumably due to the drive-unit's free-air resonance, and the gentle rise in impedance above 10kHz is due to the voice-coil inductance. The glitches in both the magnitude and electrical phase traces between 2 and 3kHz suggest the presence of some sort of resonance in this region.—John Atkinson

Fig.1 Grado SR60i, electrical impedance (solid) and phase (dashed). (5 ohms/vertical div.)