Yamaha EPH-100

This is yet another IEM offered by my dear friend, Inks: Yamaha EPH-100. According to the manufacturer, EPH-100 is geared up with a super-compact Φ6 mm dynamic transducer, which delivers sound with lower distortion. That sound really intriguing!

Unfortunately, EPH-100's ear sleeves are just too thick to be fully inserted into the ear simulators without tinkering, so measurement data listed below have been acquired sleeveless, fully inserted up to the reference plane. (you can never get to this depth with stock sleeves)

PRO: What a pleasant surprise; Not only EPH-100 delivers a superb sound with virtually no distortion, its frequency range also extends really high.

CON: Left and right channels are slightly mismatched, but it is not big of a deal. Ear sleeves are little too large, even though the IEM itself is very thin. Also, the sub-bass response is just too much with lots of delay. You can say the bass is slow, but at the same time, the delay creates a sound stage of its own.

ON SECOND THOUGHT: In order to properly address the practical aspect of EPH-100's insertion depth, I used  proprietary external ear adapters. The plot on the top shows when EPH-100 is inserted as deep as it can get with stock sleeves. 

The one on the bottom shows the same response on the left channel, with the insertion depth at its shallowest. As expected, insertion depth is not much of an issue here, due to the very low acoustic output impedance of the 6mm driver. This is amazing; the driver is actually working independent from the load(ear canal) impedance!