A portable headphone is a headphone that is used on-the-go. Portable headphones tend to be smaller, more lightweight, and may have features that lend themselves to listening on-the-go, like carrying cases or collapsible headbands.
Cons - separation and detail could be better, grainy highs, short lead
These are underrated on headfi, I find them to have an airy wide soundstage with a warm bassy sound signature. They have a warm midrange, 70's jazz with electric piano sounds wonderful. Treble is not that smooth but is just right in the mix, extension is good. You cannot pin-point instruments with accuracy though due to the sound not being very detailed and focused although it is very adequate for the price paid. I will be selling my Philips shp8500 because the Koss have a warmer midrange and airier soundstage. I think they have a unique sound of their own due to the midrange tone. The bass is quite punchy and was a pleasant surprise when I first heard them, although sub bass is nothing to shout about.
Performs very well for its price. The bass is good and extends fairly low. Some rattling might occur if you crank it up quite a bit, though. For the price the audio quality is definitely not bad.
If you hook them up to a good source and watch a movie they can achieve quite the soundstage as well.
Comfort & design
They are reasonably comfortable and very light-weight, though after a few to several hours the ears may start to get a bit sore due to not enough space between the ear and speaker. For an over-ear design they are a bit small and people with big ears can expect more of a supra-aural design as they are likely to not fully encompass your ears.The fake leather padding will make your ears sweaty on hot days and it will crack and fall off after a few years of usage. The headband is made up of some sort of mesh, which is quite nice and comfortable. Overall in terms of build quality they feel cheap, but I have had them for ~8 years and they still work. Due to their open design they will also act as a pair of bassless speakers if you like and they are therefore pretty useless out in public which sort of makes their portable style not very useful.
The cable is short (1 m) which might be good when using portable devices but not for home/PC use. It also began to be quite a hassle after a few months as it began to curl and twist around. As can be seen in pictures, the cable splits into two as it enters both cans at the bottom (dual entry design); creating a loop where its very easy to get stuck with your hand in and accidentally pull the cable and the headphones down and possibly damaging them.