I don't know that you could call the ESP950 or Sportapro popular headphones and until about a year ago or so, no one here would touch the T50RP. The Portapro, which I believe has the same drivers as the Sportapro, is a very popular headphone, especially in Europe where they're easy to find in brick & mortar stores.
Tyll has posted tests of 2 Thunderpants on innerfidelity.com. One measured spectacularly and another not so much.
http://www.innerfidelity.com/headphone-data-sheet-downloads
http://www.innerfidelity.com/content/diy-orthodynamic-headphone-measurements-and-contest-page-2
Edit: I think it's great that Tyll is measuring vintage and DIY stuff. I sent him 3 of my vintage orthos and the same article that has the measurements of those has measurements for 2 K340s. I know someone has sent a pair of Sextetts to be measured too.
Edit2: There are 6 graphs for the Portapro on Head Room, FR, THD for a 500Hz sign wave, isolation, impedance, and 500Hz and 50Hz square wave response.
Quote:
Originally Posted by
Acreo Aeneas 
Also you mention the "Sporta Pro", but then you say the "Porta Pro". Did you mean the Porta Pros or this other model, the Sporta Pro (which I've never heard off in the Koss line up).
The SportaPro is the PortaPro with a different headband
http://www.koss.com/koss/kossweb.nsf/p?openform&pc^pt^SportaPro
Edited by scompton - 7/26/11 at 7:22pm