This may not be the most audiophile-like question, but what is the size of the drivers in them? There is not a single site on the internet that I can find what sort of driver is in these bad-boys! I'm assuming a 30mm from the pictures I've seen. From what I remember about all the differences in Koss models, the SportaPro uses the same drivers as the KSC35 (not to be confused with the more well-known and popular KSC75). The drivers themselves use the same shells as the PortaPro drivers (in black instead of blue), but I believe they are titanium coated, which leads to the difference in The KSC35 and KSC75 have different drivers. Putting different drivers on the different frames and enclosures results in different sound as well, I can tell you this from experience. For example, here is how I would rank the following in terms of sound quality: KTXPRO1 > Porta Pro drivers on KTXPRO1 frame > Porta Pro > KTXPRO drivers on Porta ^ KPH40 (pphb) = KPH40 driver / capsules / pads on a Porta Pro headband. Porta Pro = Drop version As you can see the measured difference is minimal. The differences could be due to the observed difference in the rear cup, pads, or just positioning upon measurement rig coupler variance. Compare to solderdude's measurements. He also demonstrates First introduced in 1984, the Koss PortaPros have been a definitive staple of the portable headphones market for 25 years. They have survived through multiple model-line changes and their drivers have become the basis of the SportaPro and KSC55 street-style headphones and the KSC35/KSC50 clip-ons.Read more about 1 year ago. The Koss Porta Pro are a slightly better headphone overall when compared to the Koss KSC75. The Porta Pro have a better-balanced sound and a more comfortable on-ear fit that you can wear for longer than the KSC75. The Porta Pro also have a better more durable design, although not by much. Koss Porta Pro Limited Edition Rhythm Beige On-Ear Headphones, in-Line Microphone, Volume Control and Touch Remote Control, Includes Hard Carrying Case, Wired with 3.5mm Plug, Rhythm Beige. $59.00. Buy On Amazon. Koss Porta Pro On Ear Headphones with Case, Black / Silver. $39.00. 73 votes, 17 comments. 1M subscribers in the headphones community. A place for discussion, news, reviews and DIY projects related to portable audio… vix1.