After having all those $99 black friday liquidations with Triple.Fi 10 Pro for three consecutive years, it was quite obvious Ultimate Ears, which is now part of Logitech, were coming up with a new generic type IEM. Triple.Fi 10 Pro was expensive, bulky, and not quite accurate in terms of human ear acoustics.
And finally, in 2012, Logitech introduced UE900. Are they any better than Triple.Fi 10 Pro?
PRO: The frequency response extends up to 20 kHz. Extremely low distortion for a balanced-armature driver equipped IEM. Even considering UE900's quad-driver configuration, the impedance characteristic is very linear. Newly-implemented MMCX connectors are very durable, effectively eliminating durability problems involving while removing a cable.
CON: As expected, no consideration in the diffuse-field reference. The polarity has been inverted.
ON SECOND THOUGHT #1: Unlike its predecessor, UE900 becomes much more linear in terms of the diffuse-field reference when the IEM is underdamped. Thanks to the nice crossover design work done by Logitech, an electric damping doesn't affect the IEM in harms way at all.
The higher the output impedance of the amplifier, the flatter UE900 will become. (To be more technically accurate, the output will follow the impedance characteristic)
ON SECOND THOUGHT #3: While simply equipping a 2200-Ohm red damper at the bore dedicated to the high frequency range, the manufacturer implemented a special pinhole-sized hole at the low-mid frequency bore, something I have never seen before. This shall be discussed in the upcoming part 3, the in-depth analysis.