Headphones

Correlating a headphone's frequency response, measured at the 'eardrum' of an artificial ear, with the tonal balance experienced by most listeners under 'real world' conditions has long been the source of debate. What then is the ideal 'target' response that engineers should aim for? A simple free-field target response [cyan-coloured trace in our headphone reviews] matches a sound source located in the horizontal plane and 30o either side – ie, where a stereo speaker would typically be positioned. This has been superseded by a diffuse-field response [green trace in our headphone reviews], emulating a condition where the sound has no particular direction. More recently Harman's Sean Olive has modified the diffuse-field target response to provide a boost below about 200Hz [the red trace in our headphone reviews].

However, our own headphone measurements continue to illustrate the big variations that still exist in the bass and presence response of so many models. Into this mix comes iFi Audio with its 'ASP' (advanced Analogue Signal Process) and the assumption that headphones may need more bass and/or presence. This fixed analogue tone control, dubbed XBass II, offers a bass boost described as correcting a 'purely flat (headphone) response that is not correct'. The inset graph [blue trace] shows this delivering a bass uplift below 100Hz, reaching a substantial +11dB at a subsonic 9Hz. The companion 'Presence' boost lifts the midrange by +4.2dB at 1.2kHz [red trace]. With no subtle adjustment offered – use with caution. PM