Planar-magnetic headphones use very thin, flat electrical conductors to create sound, rather than a moving diaphram. As such, they're expensive, and not made often. Nevertheless, Blue has brought out its own pair of $700 planar-magnetic cans, called 'Ella' (pictured).
They have another interesting feature - an in-built 250mW amplifier that can be toggled between 'On', 'Off', and 'On+'. The On+ mode gives the amp a slight boost at 63Hz, which apparently is "just right for restoring the low-end character of music mastered in the era of vinyl".
The battery that powers the built-in amp lasts for about 12 hours, and charges fully in a quarter of that time. When you take off the headphones, they automatically power down - although the battery doesn't need to be charged for the headphones to work.
Blue's 'Sadie' headphones
Alongside Ella is another pair of headphones called Sadie which, as with Blue's other headphones, offers a built-in amp and custom-tuned 50mm dynamic drivers. Sadie is considerably cheaper than Ella, coming in at $400.
Blue has redesigned the headband for both headphones, using a four-point multi-jointed design that, it says, is "inspired by the finely tuned suspension of Formula One racecars" to provide a better seal around your ears.
It's clear that Blue is trying to bring more advanced tech to the public at a cheaper price - the Ella headphones are around £100 cheaper than their rival planar-magnetic Audese EL-8 cans - but advanced technology is no guarantee of better sound quality. We shall reserve judgement until we have heard them ourselves.