I wanted to add to this Armature vs Dynamic debate. Luckily I have had the opportunity to test 3 of Sony's XBA Single Armature earphones for review purposes. Now, bear in mind I now have a new pair of Sennheiser IE80's (warranty replacement for the IE8's I previously had). I have done a range of testing between the Sony BA's and the Sennheiser IE80's dynamic headphones with a range of music from orchestral, trance, pop, rock, movie soundtracks, and I have to say the Sennheiser IE80's outdo the BA's by miles. All my music is 320kbps MP3. I tested a pair of Sony XBA-65S, Sony XBA-NC75D (Noise Cancellation Single Armature), and Sony XBA-75B (Single Armature Bluetooth), all with no equaliser settings on my ipod, and the verdict - the Sennheiser IE80's have a larger soundstage, better treble, larger bass level and sounded more natural.
Bear in mind the Sony XBA-NC75D' retail in Australia for AU$549, for a Single Armature BA headphone with noise cancellation. I personally found the noise cancellation useless even with correct isolation because sound quality did not improve in any aspect. The way the earphones sit in your ears (horizontally opposed) means they actually protrude outside the ear, plus there is a lot of cord noise which should be heard on AU$549 earphones. To add to the mix I tried my Sony MDR-V700DJ's linked to my FiiO E11 amp via my Ipod and this is where dynamic cans come into a world of their own - such amazing audio with all music types.
Lets use some logic here, B.A. are very very small devices, originally used in hearing aids, and the basics of physics mean the smaller something is the more that has to be removed, as something will always be lost. This means that technically and audiologically (via my hearing) a Single BA driver cannot match / outdo a single dynamic driver. This is also because B.A.'s dont use airflow like Dynamic drivers do, which affects their audio range, especilly low tones like bass. B.A. cannot delivery the same range of audio like dynamic drivers can as too much has been compromised to shrink the device. I personally believe that B.A. were developed purely for the ability to shrink earphones, but you also lose quite a lot of audio soundstage. The only way possibly that B.A. can make up for their lack of audio is to mulitply the B.A. drivers - hence the quad B.A. drivers on the market, but I'm waiting for Sony to send me the XBA-4's before I can comment.
Dynamic drivers have been around for a long time, and this is primarily because they produce a greater audio range and soundstage due to their design and functionality. People say B.A. are used for size, yet look at the Sennheiser IE80's - I would say the most powerful dynamic IEM available today - it defies physics with its massive soundstage and audio reproduction quality and large range of frequencies - its an engineering marvel which only the German's have yet to pull off. Even Sennheiser themselves said they dont use B.A. because of a higher failure rate due to multiple components plus their audio quality does not match that of Dynamic. As for full headphones (cans), dynamic is always best for these due to their larger size which allows more air to be used in audio reproduction.
In Summary: My testing of B.A. headphones reveals most of the information is for marketing purposes, but when it comes to reproducing audio they are miles apart, and only dynamic drivers do the job best.