Disclaimer #1: This opportunity has been provided by Bryan, who is a frequent contributor of this blog. Had there been no support from my fellow contributors, I would've long given up on this blog. Thank you again!
Disclaimer #2: Measurement has been carried out right at the reference plane of the occluded ear simulator, using a pair of stock single flange sleeves.
Originally named as TO GO! 111, Suyama's FitEar F111 was first introduced in July of 2012, and later released in February of 2013. As a single-BA transducer driven IEM, F111 has a lot of competitors, such as ER-4 of Etymotic Research, and SE420/e4c of Shure. And of course, in order to keep their product competitive in the game, Suyama develops a proprietary technology once again. Made in titanium, F111's テーパードポートステム(Tapered Port Stem) delivers great airiness and elegant treble, according to the manufacturer.
CON: Inverted polarity
Ω is recommended, as 100 Ω seems to be an overkill.
ON SECOND THOUGHT #4: As observed in above data, Suyama's テーパードポートステム, which is an acoustic horn, lowers acoustic output impedance of the transducer, making the IEM relatively free of insertion-depth/sleeve bore related acoustic interference. In short, the horn plays a roll of an acoustic impedance transformer. According to Dr. Harvey Dillon, the director of research at the national acoustic laboratories of Australia, an acoustic horn has following effects:
"By gradually changing the diameter of a connecting tube, and hence its impedance, there is a more gradual transition from the high impedance receiver to the low impedance canal, and hence less power is reflected...Consequently, the response is less peaky, resulting in improved sound quality."Such technique is extremely useful for taming high frequency peaks/amplifying the treble acoustically at the same time, and it has been utilized for the optimization of Westone 4 previously by me.
H. Dillon, Hearing Aids, Boomerang Press, Turramurra, Australia, 2001.