I don´t understand why so many people don´t like these headphones. And IF they are loved by some people even then the descriptions of its sound differs so much that I always wonder if people were actually listening to the same headphone. I can only say that I loved them right out of the box on my portable player: the bass really goes deep (and I mean deep bass frequencies from 30-80 Hz) but does so without being pretentious, frequencies around 90-150 Hz have punch (but not that much "weight"), the lower mids are very warm and everything else above is very balanced yet a bit smoothed. Female voices are sounding fantastic, they have a body and a chest without being overtly pronounced. Compared to the Superlux HD-668 the pronounciation sucks but the presence area and upper mids are more balanced.
 
The highs are a bit problematic though: they lack bite and detail. Precision is good but celesta and strings loose gloss, brass looses its bite. Combined with the mellow lower mids the sound gets too warm, it sounds like the music is cuddled into a nice warm blanket. Furthermore I assume that the mellow lower mids are revealing the resonance frequency of the housing, there is an effect that can best be described as some kind of "distortion" which is present even on lower volumes. In short, lower mids are sounding a bit plasticky.
 
But: despite the fact that the mellowness & the missing bite are present the overall sound is quite balanced, you´ll like this headphone more and more the longer you listen to it because even with this mellow sound it manages to show bows striking strings without sounding artificial. Doing an unfair comparison to my HD-600 I prefer the bass of the HD-448; it goes deeper, has more punch and better timing (the precision on the HD-600 is superior though). The HD-448 is definitely faster than the HD-600 up to 2000 Hz or so. Then the much higher resolution of the HD-600 kicks in.
 
Furthermore, I was extremely baffled by the staging and the room response - for a closed headphone its marvellous: it is wide and fairly deep. Closely miked instruments can be observed with their own reverberation and room, yet it still is able to present the room response of the whole ensemble. This is an art I have not observed in many headphones yet.
 
I assume that my description sounds different to anyone elses'. The reason is actually very simple: since this is a closed headphone its sound depends on how you wear them, in order for them to sound good they need to seal! If your earlobes are big, your head too small or you have too much hair they cannot seal the air and they WILL sound thin, aggressive & without bass. My head is a bit bigger than usual and my earlobes are really tiny which has the result that they fit perfectly for me. Which is the reason that they are not for everyone, they simply are designed too small to fit everyone perfectly.
 
The design: on photos they look cheap. In reality they don´t look that cheap but still not that sophisticated, their price range is apparent. But once you actually touch them your opinion will be reversed because they are manufactured so nicely. Everything fits and feels good. My head doesn´t sweat even though the cushions are not made out of velour, I can wear them for long hours and nothing hurts.
 
All in all they are really very pleasant to listen to. If you like pronounced highs you have to search elsewhere, if you like your sound to be very direct and aggressive (á la Grado) you also have to search elsewhere. But if you like to listen to a warm, mellow yet balanced sound with a very good room response and staging combined with a deep reaching bass that isn´t bragging these headphones are for you.
 
Please note: My description of their sound was done using the Xonar Essence ST. On my Sansa Clip+ (they are engineered to be used on portables in the end) they actually sound a bit better: the thin and grainy sound of the Sansa tremendously helps these headphone getting a bit more aggressive and leaner.

The Koss Porta Pro is actually one of the oldest headphones still around - and it´s alive and kicking! Since I bought them, I tried several others (like Sennheiser CX-300) but I always came back to the Porta Pro. The sound mixture is just so easy to enjoy, the sonic design was done with a lot of taste.
 
They look and feel very cheap but they are surprisingly sturdy nonetheless. Much has been written about the sound: "too much bass, not crisp, etc." While this is not untrue let me explain a bit. Most portable players attentuate lower frequencies, this was a fact 20 years ago and it´s still valid today (unless the headphone output is amplified digitally). The Koss Porta Pro simply compensates for that. Also, did you ever notice while for example riding a train that when you were listening to music with a very open headphone you couldn´t hear the bass anymore? The slight overamplification of frequencies around 100 Hz also helps to compensate in that situation. Furthermore, I never had the impression that the bass sounds muddy or drowns the mids.
 
They also attentuate frequencies from 3,000 to 7,000 Hz - effectively turning them into very charming sounding headphones. While this certainly takes away some attack & drive it could be of help with harsh sounding portable players. One should be aware of this before buying the Porta Pro.
 
The rest: they have a fantastic soundstage (considering that they are portable and very inexpensive), they have no resonances whatsoever and also sound very dynamic with much precision. The fantastic soundstage comes at a cost of course: you won´t be the only one hearing your music while using the headphones in public. Your neighbours inadvertently will take part of your sonic experience, the Koss Porta Pro is - as I´ve mentionend before - a very open headphone.
 
But for me, all the cons are minor obstacles. Because I still marvel at the wonderful, realistic soundstage, the grown-up bass, the precision, the dynamic and that they sit very comfortable on my head.

I won´t repeat what everyone else wrote before - because it´s true. I´ve listened to a Beyerdynamic DT990 once and while I love my Sennheiser HD-600 a different cup of tea would be nice sometimes. But then, Beyerdynamic headphones are a bit too expensive for the sole reason of being able to listen to "another flavour". Thank God there is Superlux. You´ll get so much material for your money. You´ll also get very good, Beyerdynamic-like sound. You can even improve the sound if you replace the pleather earpads with the velour pads for the AKG K-240. I don´t know why but they sound a bit more balanced and refined with these earpads. Further improvement can be achieved by putting paper tissue between earpad and cup (increases the distance from ear to driver and will likewise improve comfort).
 
If you do these two things you´ll get a headphone that will rival headphones for 150-200 Euros: they are dynamic, precise, crisp, balanced with a very good soundstage. They are easy to drive but they will sound best with good amplifiers. They won´t be impressed by loud or harsh music, they will just play along with just the right amount of directness. Some people would argue that this makes them sound a bit "bored" - which sounds almost insulting to me because they are anything but boring. People seem to confuse balanced sound with boredom. Well, let me put it this way: if you want your headphone to colour the music you´re listening to... go and search elsewhere. The Superlux does indeed add a bit colour (around 7.000 Hz) but it´s not very much and it´s not distracting. However, lower mids seem to be a bit underrepresented - but I could be fooled about that because I´m accustomed to the comparatively (to the Superlux) warm mids of my HD-600.
 
All in all, very, very good for the money. A true bargain, thank you Superlux.
 
P.S.: before I forget... they need considerable burn-in time to sound their best.