As I have written before, I lack the necessary hardware to measure the frequency responses of headphones. And, as Keith Howard wrote in the August 2008 issue, deciding what, exactly, is the optimal frequency response for a pair of headphones is neither obvious nor trivial.

But I do look at the drive difficulty for a pair of headphones by examining their electrical impedance. The result for the Phiaton Moderna MS 400 is shown in fig.1. I wore the headphones for this measurement, and found that the fine detail of the traces varied according to how tightly I pressed the ear cups against my head. But basically, the impedance averages a fairly low 35 ohms across most of the audioband, rising above 40 ohms in the bass and above 20kHz. The MS 400s might be a little demanding of current to be used with older iPods, though the headphones' high sensitivity ameliorates the drive difficulty.—John Atkinson

Fig.1 Phiaton Moderna MS 400, electrical impedance (solid) and phase (dashed). (5 ohms/vertical div.)

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