This question could easily sit in either the fullsize or portable forums, so I will just ask it here.
I have had my Sennheiser PXC300 headphones for a number of years now (since 2007 I think) and overall have been very happy with them, owing to the superb comfort and the clear sound, particularly at low volume levels. A few years ago, however, the noise cancelling circuit died on me and I replaced the circuit after purchasing a replacement mainboard from Sennheiser. At the time, I did listen to a few other headphones, thinking I might buy a replacement for the PXC300 back then (from recollection an AKG K172 and K271 II, however neither sounded as good as the PXC300 to my ears).
Recently the noise cancelling circuit began mucking up again, so I think it is time to consider a new headphone. And before you ask, the headphone actually works like a sea shell to your ear if the noise cancelling circuit is not engaged, making it a very distracting listening experience. Apart from that, as I have improved my transport and DAC, I have found that I have been able to lower my listening levels even further (to an average of around 56 dBA for large scale classical) - to the point where the hiss from the noise cancelling circuit is now quite distracting in quieter orchestral passages - even though the hiss is no louder than it was when I first bought them (I tried an alternative pair of PXC300 and the hiss levels are the same from both of them).
I am perfectly happy with my Musical Fidelity XCan V8 headphone amp and will continue to use this with any headphone I decide to purchase.
The problem is that I have some very strict criteria for purchasing a replacement, owing mainly to health problems as well as the desire for very good isolation. I have neck problems (fibromyalgia) and likely cannot use a heavy headphone. Infact I think my limit would be phones around the same weight as the Sennheiser HD600 / HD650 series, but I would really prefer something even lighter than that. The PXC300 have been perfect in this respect). Additionally, my ear canals are extremely sensitive and get irrated quite badly with IEMs, especially any with silicon tips that need to insert deeper than just a short, foam tip like on my Shure SE215. And apart from that, most IEMs are not intended for use with home-use headphone amplifiers anyway, being more optimised for direct connection toa source or a portable headphone amp. As I am not changing my home headphone amp I need to get something that will be compatable with the XCan V8 (I plugged my Shure SE215 IEMs into the XCan V8 out of curiosy and heard a quite an annoying hiss - I am not sure how much this has to do with the high sensitivity of the IEM, the low impedance or both). The PXC300 do not hiss at all if I turn off the noise cancelling, and they are much higher impedance (150 ohm I think) and have average sensitivity (107 dB).
Anyway, the criteria I have set are as follows:
1. Must not require insertion of any sort into the ear canal (so IEMs are out).
2. Must be a closed design and offer very good passive isolation from external noise.
3. Must not be noise cancelling (I don't mind the effect noise cancelling on my PXC300 has on sound, but I do mind the hiss produced from the circuit).
4. Must not weigh more than something like a Sennheiser HD600 series, but I would much prefer something lighter than this.
5. Must have impedance and sensitivty characteristics that match the XCan V8. I don't know what the limits are here, but the XCan V8 will definity produce a hiss when certain combinations of low impedance and high sensitivity are used.
6. Price range $500 - $800. I could stretch to the $1k mark, but it would have to really be worthwhile versus the $800 limit I have set.
7. In terms of sound, I want very high levels of clarity and I want the headphone to sound very good at low volume levels. It needs to excel with acoustic music, particular mass bowed violin sound. I hate overdone bass so I want the headphone to be neutral at the low end. If you look at the frequency response graph for the PXC300 at Headroom you will see it is rolled off in the bass almost like a small standmount speaker. This suits me perfectly fine as would something that is neutral or perhaps at worst just very mildly lifted at the low end.
So I have looked around trying to find something that fulfills the above criteria and I can't really find anything. The closest thing I could find was the Beyerdynamic T70, however that is possibly over my desired weight limit, though I would only know if it was or wasn't through actually using one.
Can anyone think of anything that fits my 6-point criteria?