2014 is shaping up to be the year of ribbon headphones. First, the weird O'bravo hybrids were announced:

http://www.obravo-global.com/Product/Overview.aspx?Id=24
http://www.obravo-global.com/Product/Overview.aspx?Id=25

It's going to come in two flavors, one with an AMT (air motion transformer) driver and one with a ribbon. Both will use a dynamic driver for the bass. For those who are unfamiliar with AMT drivers, they're sort of like accordions in principle. They move air by pushing against themselves, only it's on a much smaller scale rather than the large contractions of an actual accordion. They're primarily found in speakers, and have been quite popular in desktop models like the ADAM ARTists. However Precide still makes some AMT driver headphones no one talks about anymore. Oh, and just for some history: Precide helped manufacture the original e-stat Jecklin Floats back in th' day.

http://www.precide.ch/eng/english.htm

The ERGO AMT is an incredibly detailed headphone, but it has next-to-no bass. Seems reasonable then for Obravo to pair it with a dynamic driver for those duties. As for the other ribbon model from Obravo, I'm assuming it uses their newly developed folded ribbon tweeter, so in a sense it's probably similar in structure to the AMT driver which is folded / pleated rather than an e-stat which is a flat sheet suspended between stators. In this sense it's not a "true" ribbon driver. Also of note is that these headphones from Obravo don't seem to require any special amplification, whereas a true ribbon and the ERGO AMT headphones mentioned above do.

So, what is a true ribbon driver? As far as I know it's a planar manipulated by a magnetic field, sort of like an orthodynamic / isodynamic, but it's a single strip suspended in a magnetic field between rows of magnets whereas an ortho is a coil of fine wire traces on a diaphragm with single magnets on one or both sides. In both cases however changes in the magnetic field are what manipulate the diaphragm. Why haven't we seen headphones using ribbon drivers before then? Well, there seem to be some practical challenges to overcome such as their extremely low impedance which can be lower than 1 ohm.

Enter RAAL.

http://ribbonheadphones.com/
http://ribbonheadphones.com/downloads/Earfield_Headphone_Development.pdf

They're planning to release a true ribbon headphone along with its own proprietary amplifier. Before I go any further, I should mention that I talked to someone from RAAL about these and was told that they'll sell for around $2500 USD as a set (amp + headphones) whereas additional ribbon headphones will cost $1200 USD.

Anyway, reading that second link to the PDF will give you some interesting tidbits. For instance they equate the sound of pleated ribbons to "torturing aluminum foil" --- LOL. They're proud of the fact that their ribbon is a flat sheet instead, which they say eliminates resonances. Additionally they note that a ribbon when used in a headphone as opposed to a loudspeaker is obviously going to be closer to your ears, so you're going to ear even the faintest residual artifacts, so they went to extra lengths and use a special sort of embossing to break up standing waves that form on flat surface s. Interesting. They're also keen to point out that true ribbons are woofers whereas other drivers are tweeters, so they don't need to use acoustic chambers to get bass out of them.

In addition to RAAL, there is apparently one other (as of yet unknown) company working on a true ribbon headphone.

There's also another company working on a hybrid like the Obravo. This headphone will use a beryllium foil tweeter for highs and mids and a beryllium diaphragm driver for midbass. It's slated to be released by the end of this year for---get this---$5,500 USD. The best part of all? It's made by Westone. Yeah, the earphone guys.

http://www.hifiplus.com/articles/ces-2014-headphone-earphones-and-related-electronics-part-3/?page=4

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TL;DR

I figured it was time to make a thread about ribbon drivers and their application in headphones. Several high-end products to that effect are slated for release this year and beyond, so we'll be seeing (and hearing) more ribbons in the future.