Some info on the Senn PX90...
Freq.Resp. - 20 - 20,000Hz
Impedance - 32 Ohm
Sensitivity - 108 dB
Weight - 68 grams
Cable - 1.2m right angle
Price - $40 -$50 depending where purchased
Warranty - 2 years
I saw the PX90 on sale at My Memory UK(mymemory.co.uk) and, after finding a discount code, I got them for $29.91 shipped to the US. About 10 days later they were released in NA for their usual $49.95 price. Places like J&R sell them for $39.95 even upon release.
As in the first pic, they are marketed like a sports oriented phone. With the running man, yellow trim reminiscent of the Addidas line(which they are not part of), and talk of sleekness and light weight. To me, they are somewhat of a mix between the sports line and the PX100-II/PX200-II phones.
A bit different from the other PX phones in that they are dual entry and have a RA plug instead of the others single entry and straight plugs. The PX90 have a thinner/lightweight cable that has a cord slider actually. Not that they can get tangled but, most likely, to help keep from snagging while being active. Oddly, the PX90 only fold flat, not up, like their slightly bigger brothers. They come with a strange little rubber insert to put on the headband if you desire; possibly to make them not slide if more active. I never put it on.
Sennheiser has the bases covered with their three phones. All are a bit different in form and function and even performance. The closed PX200-II is the only closed one and the only one with a volume control. The other two are open phones.
The PX90 while very balanced and even performing, almost max out players and could use an amp to tighten up/sharpen notes and give more headroom. The PX90 may not be able to be cranked if one wished since the headroom might not be there. For example my Clip+ and S639 are both within 3 notches of max volume indoors. I would expect this to be the big complaint about the PX90. Just enough volume for me even outdoors but there is no room to spare so take that into consideration.
Balanced, even, and smooth. Bass, mids, and treble perform similarly well unlike the PX100-II which has boosted bass/thickened bass and boosted treble. Also unlike the PX200-II which is great in the mids but starts to fade a bit in performance towards the ends of the spectrum. The most well behaved and a bit polite. Not as shouty as the PX100-II nor as clear and open like the PX200-II. The thicker donut pads make the PX90 sound a few rows back from the PX100-II but still not as separated as the PX200-II. A real middle ground between the other two phones, the PX90 holds it's own. A bit smoothed over especially due to it's need for juice it is not quite as resolving as the other two. Quite close but It doesn't sound as tight as the PX200-II nor does it have the sparkle that the PX100-II's boosted treble gives it.
A really good little phone. A bit odd. It doesn't fold up. It doesn't isolate nor does it have the headroom on the volume to turn it up. It also doesn't have added bass or treble to account for loss to outside noise. I would still choose it over the other two actually. I like the few more rows back presentation over the PX100-II's. I think it has better SQ than the HT-21. It needs juice but it still sounds less underpowered than my K430. It is lighter and has a much lower profile than the K430 and PX100-II/PX200-II. The bass amount is more than the PX200-II yet not as thick as the bass of the 100-II. This works works with most sources; especially good if there is no EQ to tweak. They sound more clear than the PX100-II with my minidisc recorder which has a bassier signature and they work better with my portable radio than the PX200-II since they can smooth out hiss and have more bass. The PX100/200-II headbands with padding equates to 9mm x 14mm while the PX90 is a very low profile 1mm X 6mm. I also think the PX90 look better and, like their numbering, are about 90% of the performance at a much cheaper price. Though just released here in the states, the price has not had a chance to drop yet.
Just a basic summary trying not be too long-winded. Feel free to ask about anything I didn't cover or glossed over. And also remember they have the behind the neck variant PMX90 out as well for those that might want that form factor. Thanks for reading!