Headphones

Inevitably the central question for the Ultimate One is: does it really behave like an upmarket beryllium-diaphragm headphone when it costs a tenth the price? Starting with sensitivity, it's a little below average. KLH claims 97dB for 1mW, which corresponds to 111.9dB for 1V across the nominal 32ohm impedance. We measured a little less than this – 109.4dB at 1kHz, averaged for the two capsules – which is roughly 6dB lower than typical for a modern moving-coil 'phone. However, impedance is a little higher than specified, the left capsule having a minimum of 33.8ohm and a maximum of 38.7ohm across the audible range – a variation sufficient to cause only small changes in frequency response of 0.25dB for a preamp with a 10ohm source impedance, or 0.53dB via a 30ohm source.

Uncorrected frequency responses for the two capsules [see Graph 1, below] indicate an obviously shelved-up but well extended bass, and more energy than typically seen immediately above the familiar 3kHz peak. In the diffuse-field corrected response [green trace, Graph 2], which more closely matches perceived frequency response, these features result in a distinctly shelved-up bass and upper treble. Normally this could be expected to result in something of a 'boom and tizz' tonal balance but the fact that the Ultimate One is sensitive to the quality of its earpad seal, losing a chunk of bass output if the seal is compromised by, for example, hair or spectacles [see Investigation, HFN Aug '19], suggests that many users will experience less bass emphasis than the graphs suggest. But this will be hit or miss, varying between users. The point of using a beryllium diaphragm, of course, is that its superior stiffness should render it much less prone to breakup resonances. And indeed, the Ultimate One's CSD waterfall (not shown) is unusually clean except for a high-Q mode at around 6kHz. KH