Weird conclusion regarding the stero imaging. You could say the same for the hd800, or even the stax 009.
Background sound kills the stereo imaging, bs.
I personally find the soundstage of ksc75 pretty good (illusion of space taken by the sound) , but their sound is not enough clean,
to talk of true/good stereo separation.

Not a weird conclusion.

Yes, if I used Sennheiser HD 800 or Stax 009 in a noisy place they could not sound as good as in a quiet setting and stereo imaging would definitely suffer. But they are not intended for this type of use and in any case they start with world class imaging, not poor imaging.

I found the the KSC75's imaging poor even in ideal conditions i.e. used in a quiet environment with no extraneous noise and attached to something that can drive them easily to reasonable levels. It's not as good as other 'phones I had to hand to make a comparison, which are:

Shure SE215 (IEM - closed)
Sennheiser HD 500 (headphone - open)
Sennheiser MX 5 (earbud - open)
Sennheiser CX 95 (IEM - closed)

The KSC75 are described by Koss as follows:
"The ideal active headphones for music lovers living an active lifestyle."
"Perfect for travel, the KSC75s deliver outstanding sound at home or on the move."

So it's reasonable to try them in those circumstances. If you find Senn or Stax making similar claims about the suitability of the HD 800 or 009 for travel and activity use then I'll begin to take that particular criticism seriously (maybe) but as it stands it is a bit silly.

Background noise is obviously a factor in stereo imaging because noise substantially narrows the dynamic range and negatively affects the ability to clearly distinguish different sounds and quiter sounds may be completely masked. The illusion of a coherent soundtage and of position within it is broken. I'm surprised it's neccessary to state this but you did actually write:

"Background sound kills the stereo imaging, bs."

",bs" offers no information or argument. It isn't a useful comment. Why even bother?

Your final sentence decribes the stero imaging both as "pretty good" and then "sound is not enough clean,
to talk of true/good stereo separation".

Both cannot be true at the same time.

The Koss KSC75 do have some positive aspects but when it comes to soundstage they are very firmly in the class of "a bit on the left, a bit on the right and some sound on the front of the head".

I've been using the KSC75 again today with my iRiver H140, my Sansa Clip+ and my PC with C-Media CM6206 based USB soundcard. I've also been using my Senn CX 95 and Shure SE215. I've got the KSC75 on right now while I listen to the CD that I think has the best soundstage of any I own (York Bowen's Symphonies 1 & 2 ; BBC Philharmonic, Sir Andrew Davis). I'm completely confident in restating that both the CX 95 and Shures offer much better stereo imaging, and even the MX 5 buds do this a little better.The Koss KSC75 have some good qualities but the ability to create a coherent soundstage is definitely not among them.

No I make a distinction between soundstage & stereo imaging. The soundstage, is how much space the sound takes around you, and I found it's good. It definitely doesn't sound narrow or "on your face" such like the hd25 II 1, and I like that. However, if you want to locate were the sound comes from, then the ksc75 ar not so good, the image is "fuzzy". I find useful that you can hear background sound while doing jogging on roads, this avoid accidents. Try the pmx980 from sennheiser, they are intended for sport too, and exact same "flaw", which is actually for me an advantage.

I don't differentiate "stereo imaging" or "soundstage" because they are different terms for the same thing: "the illusion of of directionality and audible perspective......the impression of sound heard from various directions, as in natural hearing" to quote wikipedia.

If you prefer your own definitions of words that is up to you but when trying to offer an assessment I do my best to use words in accordance with their commonly known definition and meaning so as to avoid needless confusion or ambiguity.

The KSC75 do not do a good job of creating that illusion so I described that. They can be at their worst when used in the street. This is a notable problem in a phone intended to be used with personal players, so I noted it. I am hardly being unfair.

The lack of isolation is a positive feature in some circumstances and my review details this perfectly well. I specifically mention the KSC75 as being great for runners and also note they are a good choice when you need to be aware of your environment. It's all there if you care to look again. But it's also legitimate and sensible to describe the drawbacks of this in terms of impact on sound quality and to mention the social difficulty of using non isolating phones in travel or in public places or work places.

The KSC75 are not the only open, portable phone I have. If I tried the pmx980 this would make no difference to the above description of the KSC75.

I described both positive and negative features of the Koss KSC75 in normal use and as they are apparent to me, and I made some comparisons with other products I own and use in the same way and that are intended for similar use. That is quite a good basis for a review.

The purpose of my review was not to simply make a list of positive attributes in order to please people who are fans of this product.

All right, I obviously offended you with the word bs, but I just find weird to criticize the ksc75 for offering no isolation, as it is obvious just by looking at them, and just like any ear bud. It is trivial that an iem, or a closed headphone would offer more isolation.
I didn't pay attention to the marketing that surround the ksc75.
The definition of soundstage seems to include both placement of sounds and spaciousness ("space and size of performance" ) , according to:
http://stereos.about.com/od/glossary/g/soundstage.htm
My finding , is that the ksc75 offer a nice feeling of spaciousness, at least compared to my hd25 II 1.

I wasn't offended. Critical comment can be interesting and informative but saying "bs" doesn't qualify on either count.

I described both positive and negative aspects of the lack of isolation (and of other features). Included in the phones I compared were other open and semi-open models. It's still there in black and white.

From your link:

"Definition: Soundstage is the ability to visualize the placement of musical instruments and vocalists in a music recording. A good soundstage also allows the listener to perceive the size and space of the performance venue in which the recording was made."

That is worded horribly clumsily. Soundstage is an ability? Whose ability? Mine or the equipment? Or the recording hardware's? Or the engineers'? It twice uses the word soundstage in trying to define the word soundstage.

Anyway the intention and meaning are probably apparent, so:

by the criteria above the Koss KSC75 is less good than the other 'phones I compared it with. Even if you really really like them I am not going to say otherwise because my purpose is not to please or displease you or anyone else, it's to offer an honest description of my experience.

I wrote a review. It's a description and assessment. It's not a post in a fanboi appreciation thread so it needn't read like one.

You can write your own review if you like. Mine stands.

There is a currently active thread here at head-fi where people claim the KSC75 is as good as or better than their Grado PS 500 or Beyerdynamic DT 660 and other good quality or well regarded 'phones. Some of them claim that people who don't think the Koss 'phones are better than everything else are failing to see the truth due to psychological deficiencies or sheer ignorance. Perhaps they are right. If that is the kind of thing you prefer to read it can be found at koss-ksc75s-dont-forget-about-this-giant-killer-in-all-the-hype

These are not giant killer, and I've never considered this point.
They are a nice entry level headphone, for people that just want have some fun, without spending a lot.
You can get bored by much more expensive headphone, even if "technically" the sound quality is better.

They probably were a "giant killer" when they came out over 25 years ago (Porta Pro, identical driver in a headband). If I'd known these when I first bought a seriously good portable player (Walkman Professional WM-D6C) over 20 years ago I would have been very impressed because the competition was poor. IEMs hadn't been invented and ear buds and small 'phones were mostly quite bad. Good phones cost a lot. But it isn't 1993 and there is high quality competition at amazingly low prices. When you can buy the seriously good Sony MDR V-6 monitors for US $55 then $15 or $20 for the Koss is no longer something that offers an experience you couldn't otherwise afford.

Another thing is that my Walkman Pro put out 30 mW per channel into 32 ohms. That is several times as much power as most personal players these days (I think that is about 3x the power of a Sansa Clip+ and twice that of an iRiver H340/140). The Koss work best with a powerful player and these days that means an amp. But if you can afford an amp why bother with the Koss? You can get better phones that work properly with modern portables instead. So an ex "giant killer" imo and too many drawbacks.

Take me to 1993 and it's 5 stars and I'll be a fanboi.
In 2013 it's 3.5 stars and it could have been less.

I actually think the sansa clip+ is not a very good match for the ksc75 , but this doesn't bother too much, as I find them still convenient for jogging.
It's true that on other sources, they can be more rewarding . I notice much better clarity with my cowon s9 player.
I'm not sure it's just amp related.

I think it probably is power related. Clip+ like you say is clearly not a good match and struggles to drive the Koss. My iRivers have about a third more power and are better. My USB sound card is more powerful than the iRivers and better again. Best so far, and by a very long way, is my old (1999) Sony ZS-M50 CD/MD/Radio domestic portable player which is much more powerful than the USB audio. This is actually a nice combination and I'm genuinely enjoying the KSC75s with the Sony. They now sound like real headphones. I don't see how anyone thinks they sound good with players that can only put out aprox 3 or 5 mw into 60 ohms. They need power.

Packed away in a box I have a Hi-FI Sony CD player and powerful Yamaha receiver so I will try those tomorrow.

I'll add some more praise for the KSC75s, something I hadn't expected to be doing:

Today I unpacked my very old (1990s) Yamaha RX-V496RDS receiver, connected it with TOSLINK to use SPDIF pass through from my PC's ALC888 integrated audio, connected the Koss KSC75 to the Yamaha's headphone jack and have been playing lossless audio (flac ripped from CD). The amp is receiving untouched stream and running with DSP effects off and tone and balance controls at neutral.

I am very impressed and surprised at how nice this sounds. The Koss KSC75 work really well with this kind of amplification (the kind not found in typical personal players). My budget USB audio card makes the Koss sound a bit thin and harsh while with the Yamaha voices and instruments are warm, natural and very well defined. It is a real pleasure to listen to. The lack of weight in the bass didn't disappear but is not nearly so obvious because the overall sound is much more attractive, and very different than when driven without enough power. I also unpacked an old CD player, Sony CDP-XE570, and that was pretty good using it's headphone jack (when at 0 dB). I had forgotten how good this old kit can sound and how underpowered personal players and USB devices usually are.

Used in the same way my lower impedance Shure SE215 and Sennheiser CX 95 IEMs (20 ohm and 16 ohm respectively) don't compare well at all, though of course they were not designed to be connected to powerful home cinema amp and they they have the bass boost, partly intended to mask environmental noise, is overly apparent and definitely unwanted. They are of course better suited than the Koss when using my Sansa Clip+ or iRiver H140/340 players. I also much prefer the Shures with the cheapo USB audio.

All this has led to me now having a huge power hungry Yamaha receiver under my PC desk, doing duty as a supersized headphone amp. I'm going to enjoy it until I get the next electricity bill. The Shures and Sennheisers can go back to portable duty, giving my ears a break from stuff being jammed into them. My headphone for use at home is now the Koss KSC75. You can call me a Kosser

I will add another half star to the review rating. These can't get 5 stars for two reasons:

Price is important but not more important than sound quality.

These are marketed as ideal for travel and portable use but only come into their own when used with powerful amplification in a quite environment.

I'm tempted to test one day the dj100, just because of the ksc75.
I wouldn't be surprised if they use same driver, but you have more isolation & comfort.

Different impedance and frequency response suggest a different driver. The tests at innerfidelity.com of Porta Pro (same spec as KSC75) and Koss Tony Bennett Special Edition (DJ 100 dressed up, same spec). They measure differently in all respects.

The porta pro don't use same driver as ksc75 (I've read the ksc75 have titanium coating on the driver, while it's not the case for the porta pro),
and anyways, it's known they sound significantly different (lot of people tried both).

It's marketing. Look at these http://cdn.head-fi.org/c/c1/c1ecb077_KossKSC75diaphragmsmall.jpeg Is that titanium? It doesn't look like titanium, it looks more like gold but it isn't gold either. Like xmas decorations and fancy wrapping paper, it's just colour. You can see pics of different "titanium" coated Koss drivers with very different colouration. My KSC75 are not coloured at all like that. The only real difference is in the marketing. Titanium costs money. Which company spends extra money on research, rare materials and manufacture on the cheaper end of the range when retailing to the budget market that mostly won't notice or care. These are all the same drivers and you can see them in a variety of different colours. The black ones aren't made of coal, the silvery ones aren't silver and the gold ones aren't gold.

Difference in sound is due to the way they are mounted and fit. If you press the KSC75 to your ear they sound significantly different. If you bend the KSC75 clips to angle them they sound different. If you clamp the Porta Pro more they sound different than loose. Further up the ear they sound different than lower down. If you look at the tests at headphone.com and innerfidelity it's obvious that there isn't any difference that can't be accounted for by slightly different position at the ear.

If you take the drivers from KSC75 and mount them on Porta Pro headband, then take the drivers from the Porta Pro and mount them on the KSC clips.....they both sound better!!!!

that's a joke btw but I think I've read modding threads where that pretty much happened.

http://www.head-fi.org/t/85174/koss-ksc-35-vs-ksc-75/15

Someone wrote to Koss and asked if the drivers are the same. They are:

"Thank you for contacting Koss Stereophones. The Ksc35' and the Ksc75's
have the same sound performance but the look is different. If you have any
other questions, feel free to contact Koss.

Valerie
Koss Consumer Sales"

Koss never implied that the driver of ksc75 are full titanium, but they just have a thin layer of titanium to
change the sound (2 mm according to ads). To me on your pic, it's looks like titanium inside/over plastic. Koss is not the only company to add titanium to their drivers, there's at least ultrasone.
Titanium is not a rare metal, it's just expensive to produce:
http://wiki.answers.com/Q/Is_titanium_rare
It's certainly less expensive than gold, and often the jack connector of headphone are gold plated.
Tell me why company bother to add a thin layer of gold to jack connectors of headphones ?
It's not that expensive.

The letter from Koss states in plain unambiguous English that the drivers are the same except they look different. Measurements of the drivers show no significant difference. If you want to believe something else that's fine.

Your original reasoning is that the porta pro and ksc75 are using same driver, and I wasn't convinced.
I don't even understand why you are talking of the ksc35 in the first instance, it's a different matter.

It's a different matter but with the same driver

Relevance: people claim that of this family of 60 ohm Koss 'phones certain ones use different drivers and that this accounts for significant audible differences. In fact the audible differences are easily accounted for by position and clamping force and when measured there is no significant difference.

As for the 2 mm of titanium. Two millimetres? The diaphragm wouldn't even move. Maybe they meant 0.02 mm. Marketing copy is only marketing copy. Like Valerie from Koss said, the difference between the different drivers is the colour.

It would be good if you wrote your own review or contributed your thoughts in the forums. I'd rather not spend more time discussing my review here.