Additionally, the tiny "L" and "R" markings on the inside lobe of the earpieces aren't easily legible in low-light situations.
On a more positive note: the earpieces are very light, and I found the PFE 232 comfortable to wear for hours on end.
The PFE 232 is a proprietary Audeo balanced armature design (most headphone manufacturers using balanced armatures buy them from outside suppliers). This type of driver produces more-accurate sound than standard in-ear headphone drivers, that are, in essence, tiny speaker drivers. The PFE 232 has two balanced armatures in each earpiece.
You also get a small zippered carry case. The earphones come with a generous two-year warranty.
To its credit, I don't need to AB test the PFE 232 to hear that this is a great sounding earphone. The clarity is truly remarkable, and it has the sort of open, out of the head imaging I find hugely appealing.
The PFE 232's bass is deep and extremely well defined while the treble is vivid, but never harsh or bright. I also felt the sound was more open and less "canned" than what you get from so many in-ear headphones, including Sony's new $400 balanced armature XBA-4.
Acoustic jazz and classical music were particularly well served by the PFE 232. They turned up the heat on Rapheal Saadiq's funk, highlighting the drums' attack with impressive power. In fact, the PFE 232's spacious sound is on par with some full-size on-ear headphones like the $299 Philips Fidelo L1.
Switching over from the gray to the black Acoustic Filters adds bass, but the overall sound is still crisp and clean. I'm very happy with the tonal balance with the black filters, and would recommend their use with rock or any electric music.
The green Acoustic Filters elevated the bass even more, but also dulled the treble. The green filter is too much of a "good thing," and in my opinion it sacrificed the best qualities of the PFE 232's sound. As always, sound balance is a matter of taste, but the PFE 232 offers the chance to nudge the balance closer to what you want.
Up to this point I was listening to the PFE 232 with an iPod Classic, but considering its $599 price, I was curious to see if the sound would improve when I plugged them into a $140 FiiO E17 USB digital-to-analog converter/headphone amp. That actually made a big difference, with significant gains in transparency and detailing over the iPod Classic, but the PFE 232's noise isolation capabilities sound below par, even for universal fit in-ear headphones.
The Phonak Audeo PFE 232 is expensive, but the universal fit Shure SE535 runs $499, so the PFE 232 isn't so far out of line with other flagship earphones. It's an awesome-sounding universal fit earphone, and the Acoustic Filters offer buyers a degree of fine-tuning not available from the Shure and other headphones.