Headphones

The current crop of planar magnetic headphones typically have below average sensitivity, a flat impedance trend, well-extended bass and recessed lower treble. In every particular, the AB-1266 Phi TC fits the mould. At a measured 98.4dB SPL for 1V input at 1kHz, the sensitivity of this Abyss model is far from being the lowest we've recorded for a planar magnetic headphone but is lower than typical of even high-impedance moving-coil models and much lower – to the tune of 16.8dB – than posted by the Audeze EL-8 open-back [HFN Oct '15]. Nevertheless, the AB-1266 Phi TC is relatively easy to drive with an almost constant impedance of 42ohm across the 20Hz-20kHz audioband. The variation of just ±0.1ohm means that the overall frequency response will not be significantly affected by the different headphone amp output impedances it is likely to encounter.

The uncorrected frequency response traces – derived from an average of ten separate measurements between which the headphone is removed from the artificial ear and then re-seated – look slightly 'rough', particularly between 1kHz and 5kHz [see Graph 1, below]. This is not due to noise but the presence of multiple diaphragm resonances, another feature commonly seen in PM headphones and confirmed by a 'grassy' cumulative spectral decay waterfall (not shown here).

Some PM designs achieve an almost flat response down to 20Hz but although the Abyss AB-1266 Phi TC doesn't quite manage that, very few listeners are likely to notice. Potentially more noticeable is the curtailed peaking around 3kHz and generally reticent treble output, which may well impart a warm tonal balance and reduced presence. This is reflected in the corrected responses [Graph 2, below], all of which indicate a large hole in perceived treble output centred on 5kHz, whereas below 1kHz the corrected responses are commendably flat with at worst only mild shelving up of the bass. KH