[Updated on 04/15/2013: The impedance stabilizer has been analyzed.]
Disclaimer #1: This IEM is owned by Inks. Much thanx to my good friend.
Disclaimer #2: Unlike that of Sony MDR-F1 or MDR-MA900, the impedance stabilizer implemented on BA200 turns out to be something other than a simple voltage divider. Read on!
BA200 is TDK's top-of-the-line IEM equipped with dual balanced armature drivers. Developed by the acoustic research lab at Imation, it is claimed to be tuned to have a very smooth frequency response, which is closely emulating the tonality of a reference loudspeaker system.
CON: The tweeter's polarity is inverted & the high frequency does not even exceed 18 kHz.
up to the reference plane, which is equivalent to that of Etymotic Research ER-4, in order to retain its signature linearity. This is not a good news for the users with small ear canals.
ON SECOND THOUGHT #6: Interestingly, TDK claims they have successfully developed a ground-breaking technology, which can stabilize the impedance characteristic of the IEM. Conventionally, it is done by equipping a simple voltage divider, and normalizing the source impedance to a stable value. Thus, the transducer can be driven under a stable condition, regardless of the source's impedance. Some examples are Sony's impedance compensator, which is implemented on MDR-F1 and MDR-MA900, and Ultimate Ears' airplane adapter. However, such technique does not take the amplifier's capability in consideration, as some amplifiers might introduce oscillation upon a reactive load.
That is why TDK comes up with a Boucherot cell, or a Zobel network, which is widely used for stabilizing the voicecoil inductance of a loudspeaker. In constrast to Sony's approach, which alters the output impedance of the amplifier, TDK's approach alters the impedance of the driver itself. According to their patent, US20130028437, the impedance stabilizer flattens out the overall impedance characteristic of the IEM.
Unfortunately, the electroacoustic effect of the stabilizer can not be assessed, as there is nothing known about the TDK BA200's transducer unit. If anybody has opened up his/her BA200, please let me know what is inside!