Headphones

In recent years a new generation of isodynamic (aka planar magnetic) headphones have overturned this design principle's earlier reputation for low sensitivity. The Empyrean is far from being a low-sensitivity example but our measured figure of 109.3dB SPL for 1V at 1kHz, averaged for the two capsules, sets it somewhat below the state-of-the-art in this respect. We recorded 115.2dB from the Audeze EL-8 open-back [HFN Oct '15] – the best we've measured from a planar magnetic thus far. The open-back version of the EL-8 has an impedance of about 31ohm, which is only a tad less than that of the Empyrean (which has a measured impedance range of 32.6-33.2ohm over the 20Hz-20kHz audioband, when worn). In practice, this swing in impedance is sufficiently small that any variation in frequency response, due to finite source impedance of your heaphone amp, will also be negligible.

The uncorrected frequency responses for the two capsules, averaged from ten measurements per channel between each of which the headphone is re-seated on the artificial ear, are entirely typical of isodynamic headphones [Graph 1]. The response is essentially flat below 1kHz with excellent bass extension. Also typically, the peak at around 2.5kHz is lower than conventionally considered necessary for a neutral tonal balance. This is reflected in the third-octave corrected responses [Graph 2], the diffuse-field trace indicating that the Empyrean has a bass heavy/treble light perceived tonal balance, although the Harman curve [red trace] indicates a more neutral balance below 1kHz. The ripples in the uncorrected responses between 200Hz and 1.5kHz are matched by small ripples in the impedance versus frequency response, suggesting they may be caused by diaphragm resonances. A CSD waterfall (not shown) confirms the presence of some resonances below 1.5kHz – an unusual feature – but at a reassuringly low level. KH

Sensitivity (SPL at 1kHz for 1Vrms input): 109.3dB
Impedance modulus min/max (20Hz-20kHz): 32.6ohm @ 4.3kHz 33.2ohm @ 157Hz
Capsule matching (40Hz-10kHz): ±2.0dB
LF extension (–6dB ref. 200Hz): <20Hz
Distortion 100Hz/1kHz (for 90dB SPL): <0.1% / 0.1%
Weight (headset only): 436g
Price: £2700