Seriously, these things are built to last. When the apocalypse occurs in 2012, this Sennheiser would be left intact (maybe the wires would get destroyed). And for future generations of the human race (or whoever takes over the earth), they would be a relic of the old world.

I own two pairs, one for work and one for portable use, I treat the portable headphone with utmost care, like a baby, while the one for work gets tossed around and daily abuse, and yet both look the same. On a note of the clamping force, the frame needs to burn in, so that the force loosens and optimum comfort is achieved.

Sound. How does it sound? It's a bit colored, I think. Definitely not neutral, but I've gotten over the "neutral stage" where I cared about neutral headphones, I just want to enjoy my music with clarity. The bass mids and highs are fairly even in terms of balance, but not perfectly balanced. What's very noticeable is that it has punchy bass like a Grado, not deep rumbling bass. And absolutely no soundstage, which creates intimacy, or in my case, that in-your-face-sound that you get from Grado. I use these for speed metal, thrash metal, power metal, traditional metal, etc. Metal that's fast and guitar driven. They're like a closed back Grado, but not as bright.

I got it for free from work, as this is what they use for their stuff such as recording, calibration, etc. They previously used V6's, 440's and T50RP's, but they settled for the HD 25-1 II. There is a huge increase in price to the consumer, but I'd imagine when a company purchase these, the difference is not all that great. They are the basic edition, but I wish I owned a pair of the Adidas versions.

Sound comparison to the hf5:

Slight increase in bass (may be due to the dynamic driver moving air). Drum kicks and low bass feel more realistic on the mc5, however the bass is of higher quality on the hf5. It's a good compliment if you love Ety's sound with a bit more kick in the bass. And it responds to equalization much much better than the hf5, I could turn this into booming bass monsters with a degree of clarity being remained. Lovely.

Lastly the treble isn't as bright and rolls off earlier than the hf5, this could be a good thing or a bad thing depending on what you want. The mc5 while being a lower model above has some advantages due to its dynamic driver, but in terms of speed, detail retrieval and clarity, the hf5 murders it.

I ended up returning it, I have a much better DD IEM: EX600. The mc5 is no slouch though, it's just that I won't use it, I'd rather use the EX600 for DD and the hf5 for BA.

...got everything else wrong. Take this mini-review with a grain of salt because YMMV with these IEMs. You may even get a great fit with comfort, but I didn't.

Tried all the tips. The gliders don't stay. The foams are itchy. The grey flanges are itchy and too big. The only one that works are the stock small flanges. They fit well and isolate well, BUT they are uncomfortable as HELL. I am considering upgrading to the custom tips or even buying some other tips, however I've seen users whose HF5's broke due to using other tips, so be careful.

The sound is great. When doing an A/B comparison to the EX600, I found that the HF5 has a higher resolution sound and weaker bass. The BA driver is much quicker than the dynamic driver, one is not better than the other IMO. The soundstage is much much smaller than the EX600.

Oh and they're exceptionally microphonic, can be worn over the ear though. But it doesn't fit as well as the EX600 which was designed for over the ear wearing.

Bass = perfect
Mids = perfect
Highs = perfect

The highs are very slightly rolled off. And I've watched a video review from Inner Fidelity which mentions grain, but I hear none. Also the EX1000 doesn't offer much more than the EX600, I cannot justify the price of that IEM.

Lots of tips to choose from, they're intimidating at first, but you will find one you like.
I'll admit I didn't like it at first due to it being worn around the ear, but that has it advantages as well.

Looking forward to the XBA series.

I don't really have much experience with IEMs, because it's rare to find one that I truly like. There is always a problem which is either the sound or fit. That said, this satisfies me on both levels and my wallet is happy.

It's not as comfortable as the Marshmallows or the Air Cushions, but it is comfortable, and that's a good thing because 90% of IEMs don't agree with me. The best IEM I've heard is the EX600 and the FXC51 can give it a run for it's money in terms of detail. The EX600 has a near perfect sound in my book along with a great fit and variety of tips, however the problem is that it's worn around the ear. Yes I know I'm whiny. Given a choice, I'd pick the FXC51.

These don't isolate all that well, due to the vented back I believe, however that's not a problem for me as I like to be aware of my surroundings. Maybe it's my ears but I have cleaned the tip of the driver twice due to earwax gathering. The earwax can actually affect the sound by creating a veil-like effect.

Interestingly the Micro HD drivers respond to EQ very very well, it's a very flexible IEM for EQ lovers, even if the signature sound is flawed in your opinion you can tweak it to almost whatever you like. I know that EQ is a sin for some of us here but if you don't EQ and you prefer an accurate tone, avoid this at all costs.

As for me, sometimes I EQ sometimes I don't. This is what the FR graph looks like:

http://goldenears.net/board/files/attach/images/783980/442/984/01.FR_JVC_HA-FXC51.png

I used these for gaming, they were perfect, the anemic bass made hearing the details easier and the large soundstage worked well with classical. I really loved these and I regret selling them, maybe I'll pick up an AD900.