So, not sure if burn in will change things down the road, and its definitely too early to give any "set in stone" opinions. But I know how antsy I was waiting for more impressions, so I'll just start with a little background and say how these are working out for ME, YMMV. And if burn in or time changes things, it will only be for the better.
I've started out with high end audio listening to speakers years ago. I moved over to headphones because of how practical they are, and I haven't always had access to a listening room to dial in speakers, etc.
I have been happy with my main headphones for a long time now, mainly K-1000s and HP-2s. And my IEMs ER4s, but I really wanted a good portable closed headphone that wouldn't be embarrassing to wear in public. My expectations were high, and all of the options pretty much fell short... due to my high expectations, mainly. As you can probably tell from my main phones, I like mostly an uncolored, neutral, natural and a detailed presentation of music, or in a word, accurate to the original recording. I can't stand excess bass or recessed treble which seem to be the standard these days.
I've either listened to or owned the follow phones:
Vmoda 80 - too much bass, not enough treble
Vmoda 100 - Way too much bass
DT1350 - One of my favorites but upper mid-range dip left me wanting more, treble sparkle missing
Amperiors - Exciting phone. Too much bass, nice sparkling treble, but upper mid-range fatigues, sibilance
Sony MDR -1R - very midfi sounding, meh at best
Momentums - excess mid bass, treble is too subdued, dark, but very warm and smooth sounding
Shure SRH-940 - Top tier detail and relatively neutral, true high end qualities for $300, problem, very ugly, cheap plastic cracks within a year, mid base is recessed which makes it sound a bit hollow and thin, but great sound for the price
AKG K550 - uneven treble, large sound-stage but somewhat unnatural, not the best for small heads
B&W P5 - not a fan of B&W speakers or house sound. Honestly, they just didn't impress.
Mad Dog's - Very good sounding, but not as extended as I would like, and I didn't like the bass presentation all that much. Kind of needs an amp to shine.
I point out my listening preference and background mainly to give you an idea of whether you might like these phones or not. I definitely do not want anyone to take my impressions of the phones listed above as absolutes. I just wanted to list the reasons they, ultimately, didn't work for ME. They all have attributes that would bring many hours of enjoyment to anyone who likes their particular sound.
Back to the M500s. The FR is almost dead neutral 20-20K. Very rich sound. Tight accurate bass, extended, even treble, nice open mid-range. By the design of these things, I didn't think such an even and extended sound was possible. The sound-stage is average for on ear. Don't expect a huge of out head experience. It is very open and airy sounding, however.
The memory foam pads are a delight. The clamp is minimal. It is very light and looks even better than the Momentums which I think look great. All the parts are high quality and luxurious looking, feeling. The case is even small and nice looking.
So, I finally found a mid-level, closed phone that checks ALL the boxes for me and gives a true high end-ish sound, top to bottom, that is musical, low profile, comfortable and looks great. Well done Kef. It's great to see a company keep their integrity by nailing it right out of the shoot rather than releasing a compromised portable into an overcrowded segment. They engineered a brand new type of driver and implemented it well.
The isolation is very unique. As you might imagine, this type of on ear is not going to block out a lot of outside sound overall, but the pads tend to muffle it in a way that causes it to not interfere with the music. Overall, the only on ear portable that does any IEM level isolation is the DT1350 which also had a tight clamp that made long term listening difficult. If you need serious isolation, you really need an IEMs.
Amping the M500 helps and tightens everything up. While amping does step its qualities up, these sound very good straight out of a phone as well. Amping is a choice, not a necessity.
I can sum it up by repeating what has already been said in this thread:
The sound is rich, liquid, extended, neutral, full bodied, musical, pretty much whatever is on the recording comes out.... like Kef speakers.
Lastly, I hate to hype anything, and these won't “blow you away” when you put them on. Like most quality headphones, these will grow on you if you like this type of uncolored, non exaggerated sound.
