The characteristics taken from the manufacturer's official website are as follows:
| open |
| waybills |
| arc classic, arc occipital |
| 15-25000 Hz |
| 60 ohm |
| 103 dB / mW |
| < 0,2% |
| foldable design |
| 1.2 m |
| 3.5mm |
| by 6.3 mm |
| 62 g |
I'll start with the set of headphones. In the box, in addition to the headphones themselves, you can find an adapter for a 6.3 mm jack and a leatherette case. 
The clever foldable design of the headphones allows them to be folded very compactly for transport. It is worth mentioning that thanks to the flexible metal bow and the hinge of the speakers, the headphones almost perfectly conform to the shape of the head when worn. At first glance, the design does not seem reliable enough for everyday active use, however, looking ahead, I will say that it proved to be excellent in 2 years of wearing in different places and in different conditions. The foam rubber remained intact both on the speakers themselves and in the place of contact with the head. The folding mechanism works as well as when purchased. The build quality and materials are excellent, which is confirmed by the excellent condition of the headphones after 2 years of active use. The paint has not peeled off anywhere and the fact that the headphones have been in use for a long time only remind of small scratches on the silver edging of the speakers. 
The only problem that I managed to face was the problem of the fragility of the cable. First, the cable hardened after wearing at a negative temperature, and then after a year of use, the contact near the jack began to move away. Replacing the jack did not help - I had to change the cable completely. The replacement was done independently. With the initial skills of soldering and straight hands, this operation does not take much time. Simple headphones from Gembird were chosen as a donor. Subjectively, the sound did not change after the cable transplant. After repair, the headphones continue to work properly for a year. 
Now it is worth saying a few words about the comfort of wearing while listening to music. With a wide range of foldable earbuds and speaker positions, the headphones fit snugly around your head without causing discomfort. The foam cushions protect the temples from contact with the headband, however, it is worth noting that after an hour or two of listening to music, there is still a certain inconvenience and pressure begins to be felt. Also, discomfort can be felt by people with long hair. Careless removal of the headphones from the head may cause hair to get caught between the temples. A lot has already been said about the sound of headphones. And there are two groups of people. The first is the fans of the sound Koss porta pro and ardent opponents, confident that Sennheiser and AKG have a clear advantage.I will not persuade anyone in this review, but I will only tell you about my impressions after listening to music in different directions and on different players. The first player in conjunction with which Porta Pro was used was a simple Canyon CNR-MP4D1G. The initially dull sound was corrected by setting the "Rock" equalizer preset. Of course, one should not expect outstanding results from a budget player, nevertheless, a fairly acceptable sound was obtained. There was no discomfort when listening, the rock music sounded bright, but dirty. Of course, the famous low frequencies could not but rejoice. 
Paired with the Apple iPod Classic 80 GB, the earbuds unleash their full potential. I was pleasantly surprised by the brightness of the sound and the powerful bass of the headphones. Listening to the Trance-style tracks was a great pleasure. By the way, on this player I also set the equalizer settings to "Rock", because, in my opinion, this added the missing high frequencies to the headphones. The volume margin turned out to be very large, I never listened louder than 60 percent. 
The last bundle - Apple Ipod Touch 3g 8 GB and Koss Porta Pro also produces high sound quality, however, I believe that it falls a little short of the level described above. 
It's time to draw conclusions and decide how the headphones have shown themselves over a long period of operation. Stylish, high-quality headphones have served almost flawlessly for 2 years and now they continue to delight me with their sound. Neither wearing in the cold, nor mechanical stress and transportation in various positions and places could fail Koss porta pro... 26 years of this model's presence on the market is not an accident, but a pattern, because such excellent products deserve the attention and recognition of music lovers all over the world.
