CES 2012: Sony
Two types of drivers are used for in-ear monitors: dynamic drivers, and balanced armature speakers (sometimes called balanced armature receivers). Dynamic drivers are significantly larger than balanced armature speakers, and as a result the final dynamic in-ear monitor will be slightly larger to contain it. This results in an earphone that can be a little more difficult to insert into the ear, and a larger chamber the sound has to go through to get to the ear canal, which can lead to more coloration of the music heard. Because balanced armature speakers are so much smaller, in-ear monitors can be designed more compactly, and with better ergonomics and fit. Also, multiple drivers can be put into the enclosure and used like woofers and tweeters in the headphones. There are downsides to balanced armatures however, as the wide impedance swing of these devices and typically low impedance, they are more likely to interact with the output impedance of the driving amplifier and color the sound.
Currently there are only a small handful of BA manufacturers in the world, the largest of which is Knowles. (Here's their BA speaker product page.) If you have a balanced armature earphone, it almost certainly contains a Knowles BA speaker. Sony has decided to begin to manufacture their own balanced armature speakers. It seems to me, Sony wishes to have complete control of the BA speakers used in their headphones. This will allow them to optimise the size and shape of the drivers and produce smaller and more comfortable earphones, and to optimise the acoustics of the drivers for use in single and multiple driver earphones. It's a bit of a risky move, but Sony is certainly a company with the resources to pull it off.
In September, Sony announced the new line of 11 balanced armature products, which includes: earphones; head-sets wired and Bluetooth; a noise-cancelling model; and a sports version. Here's Sony's press release and product page for these new in-ear cans. I listened to the basic line-up of the four earphones and felt they sounded a above average on quick listen, I certainly look forward to a real listening session for a proper evaluation of this exciting new development.
I'll let Claude Schmidt fill you in on the line.