A Head-Fi user, James444, generously loaned this IEM for analysis along with 2 other Final Audio Design's Heaven series models, A and C. Thank you! The first runner up is S, and A & C will follow.
As far as I know, Final Audio Design believes music is all about dynamics, according to 高井 金盛 (Kanemori Takai) -san, the representative director at FAD. Their design philosophy revolve around that very idea, and that is most likely how they came up with the Balanced Air Movement(BAM) technology, which is claimed to prevent acoustic leakage, while optimizing the air flow inside of the housing.
Of course, I do not believe in any type of commercially-biased claims by the manufacturer, unless the technologies are proven to be real. As shown on the above, the balanced armature transducer has a rear-vent, which is used for bass boost and pressure control. That vent must be connected to the rear volume of the housing and to the outside through slits. This is a simple venting technique promoted by many transducer manufacturers, and it seems FAD followed application notes quite well. Yes, BAM is real.
PRO: If something is radically funky, is it a good thing?
CON: The distortion figure, which is present on all three Heaven models, is so bad, the IEM is rather cult-like.
ON SECOND THOUGHT #1: These Heaven series models, including S, are truly unique, defying the common standard of electroacoustic engineering. A slightly bass-oriented tonality is understandable, but the distortion figure is far beyond human's perceptual threshold, which is 1% for music programs. The distortion becomes more audible as the volume knob turns up, and the resulting sound quality becomes somewhat close to the original TRON's background music. This kind of square wave-like modulation is never preferred for a hi-fidelity audio reproduction, but can be a good thing at the same time, especially when you listen to 70-80's SF movie soundtracks, or today's Daft Punk. It seems FAD have its own market & fanbase, and I don't think I can just judge their quality based on the common standard; I think I am going to fall in a love & hate relationship with FAD from now on!
ON SECOND THOUGHT #4: How does FAD's BAM technology affect the sound quality of the IEM? With the rear vent blocked, the sound becomes slightly less bass-oriented, as expected. Since balaced armature drivers with a rear-venting configuration do not get affected by the over-pressurization in the ear canal, I believe it is a good idea to just seal the vent off completely. (If ported all the way to the front cavity, BA drivers lose a sub-bass response) And it is important to note that the opening at the strain relief is completely blocked- it is not an acoustic vent.
ON SECOND THOUGHT #5: Upon close comparison, it seems A, C, and S are basically identical in terms of electroacoustic design at least.