Pros: Affordable for the sound quality; foldable into a really compact size
Cons: The cloth cable has a tendency to twist while folding the Pro; the open design is not good for noisy/very quiet environs
This is my first 8 hours of my portapros impression (on a intercity bus, in less than ideal environment for an open can. EDIT 1: this was on the day of purchase).
First thing that stands out: separation of a song's different elements. Made me hear more, yet still sounds fun and engaging. Prominent trumpets, horns, cymbals, etc. Those high notes sounds almost intruding in certain parts of a song. Vocals are slightly recessed compared to other elements. Bass is adequate, but not always. Bass guitars and similar sounds (cello, etc.) sounds great, but kick drum, impact bass and the like almost as if its not enough for me, and I'm not a basshead in any way. String instruments sounds gorgeous, prominent in the songs I listened to.
For curiosity's sake, I listened to my SZS playlist, the whole Coldplay - Viva la Vida album, Coldplay - Mylo Xyloto album, Bloc Party - Intimacy, and Bloc Party - Weekend at the City albums. A 30 Seconds to Mars song (The Kill), and a HD video I downloaded of The Piano Guys song called "Jon Schmidt - Michael Meets Mozart".
EDIT 1 (February 10, 2012): Now that I have listened to it more on my E10, I can say that the bass is overpowering, quite boomy and less punchy then I anticipated in the earlier stated environment. The highs are less prominent than I remember on the bus too, but is still adequate enough to be neither a bother or feeling inadequate. Vocals still sounds recessed to my liking.
Also the day before, I was using it on the Metro (subway), and certainly the boosted bass helps it sounds almost not bassy, as outside noise drowns out the bass. Of course, louder noise will drown out everything, but as far as I can hear in moderately loud noise, the boosted bass helps it sounds "balanced" for a lack of a better term and/or experience. I find it quite a similar experience as on the intercity bus.
Still haven't compared it to my CAL! yet.
Now that I have done the quarter mod (where you cut a hole the size of a quarter on the ear cushions), I can say that the problems I had before (slightly boomy bass, recessed mids/vocals and "just-there" highs) are corrected to a degree. Bass is still very prominent, but not boomy, and rumbles deep. Mids and vocals now, to my glee, are forward and prominent, yet not overpowering. And the highs achieved a somewhat more vibrancy than before.
And I also have compared to my CAL! also. Before and after the quarter mod, I can say that I prefer my PP more than my CAL!. I can't put a finger on why, but my guess is that while the PP are on-ears, the CAL!'s ear cup just exert pressure a little bit too much for prolonged wear, even after a long time stretched on books. Virtually to my inexperienced ears, they are almost the same. I feel that the PP have more deeper bass reach, but as far as I can tell that's it. Will update this after some more time.
EDIT 2 (February 24, 2012): Finally I can agree with the majority who had used this headphone; that they are bassy 'phones. At first to my ears they are not as bassy as people here made out to be, and makes less sense after I did the quarter mod. But then tonight, after a long time of constant use (to the point of neglecting my CAL), I finally hear the bassiness of it. But I think Koss purposefully made them bassy because they are to be used primarily outdoors, where there are a lot of external noise to intrude in. While they do work for low level noise (just walking around, with the occasional cars passing by) and somewhat work for medium level noise (on a bus), that they sound almost balanced, IMO, but for high level noise (in the subway) they are drowned out by the noise. In a relatively quite environment, they are bassy. A bit boomy, not to my liking, but they are for the most part still punchy and delivers deep bass too. Otherwise, my views are still the same. To my chagrin, it's 2 of MUSE albums that showed me the bass.
Compared to my CAL, I can say I like my CAL better, just because the bass aren't as boomy as the PP. Maybe I need to listen to both of those albums again.
EDIT March 5 2012
This may sound crazy, and this may just be some sort of placebo or something, but I just cut open a bit more of the earpad, and the vocals are now a little more recessed now, yet the bass and highs are somehow tighter now. Before the opening I cut out is 19. cm (0.7 inches) I expand the cut to 2.4 cm (0.9 inches).
Now I seem to slightly hate it now. :(
On the other hand, I have the HD414 pads incoming, so expect something updated by then.
I will update this when I get more time on it and get more familiar to the sound. And I will also be comparing this to my CAL!. If I remember.
This will mostly be final. But if there are anymore revelations and hidden secrets, I will add below. Hope my eclectic impressions help someone made a more informed purchase.
I lied. Now I added a felt ring "acoustic bass lens" after changing the pads to the HD414 pads. I already did the write up on my blog, and I could use some views, so here it is.