Headphones

Focal's lowering of the Stellia's nominal impedance to 35ohm pays off here, as it does with the Elegia [HFN Mar '19]. The high voltage sensitivity of 119.6dB (re. 1V at 1kHz), averaged for the two capsules, accords well with the specified 106dB for 1mW input, which is equivalent to 120.6dB for 1V. Actually the Stellia's impedance varies quite widely, from a measured minimum of 29.8ohm to a maximum of 56.7ohm, which is sufficient to cause a 1.1dB change in frequency response with a headphone preamp that offers a source impedance of 10ohm (or 2.4dB driven from a 30ohm source impedance). So to hear the intended tonal balance, ensure that you partner the Stellia with a source having a low output impedance.

Uncorrected frequency responses, measured at the artificial ear's drum reference point, illustrate the Stellia's extended bass, but also an unusual unevenness around 100Hz and a lower peak around 3kHz than conventionally deemed necessary for a neutral tonal balance [see Graph 1]. In the corrected responses [Graph 2], these features translate into a shelved-up bass response in the diffuse-field correction [green trace] but a more neutral LF balance in the Harman correction [red trace]. Nevertheless both traces agree that there is a deep hole in perceived presence band output between 2kHz and 8kHz – a feature we see a lot in modern headphones.

The Stellia's extended bass response, which doesn't roll off significantly until below 20Hz, is critically dependent on a good seal of the earpads to the head. Repeating the response measurements with a large spectacles temple bar fitted to the artificial head and then simulated hair show that this seal is easily disrupted in normal use, with the result that 10dB in output can easily be lost below 150Hz. Measurement of acoustical crosstalk between the capsules confirms the subjective finding of some headband resonance, peaking at 120Hz. KH