Disclaimer, I'm a Beyerdynamic fanboy but my review is critical.
I started with the 880 and life was good.
I acquired a 990 and found the first headphones Id ever heard that needed 0 EQ to sound optimal. They are still my go to cans.
I've heard great things about the Custom One Pro and so I picked up a pair hoping to knock the 990's off their pedestal.
Packaging: A 1 meter cable, manual, catalog, and that's it. No allen key for the face plates and no bag. Despite the premium price they do not have the soft case like the 880's and 990's did. Packaging was adequate and they arrived un damaged.
Features: The adjustable bass ports do make a lot of difference. Each setting drasticly changes the sound. These settings do NOT replicate 880, 990, 770, etc. The only thing that changes is 200hz and lower.
Cabling: A first for these style of headphones, they now have a removable cable. Which is good because the included one is far too short. They really thought only ipod users were going to buy these. The cable uses a headphone jack and should work with many after market cables. IE no mini xlr and so AKG cables won't work. The cable does partially lock in using a friction mount.
Earpads: They went with a soft lambskin type of synthetic. Good news for other Beyerdynamic owners, they appear to fit my 990's and hence the 880's as well. A nice feature is a divot cut out of the top of the ring which makes putting the ear pads back on a breeze. Push and twist, it works like those things that take tires off your rims. The cushioning is a little more robust than the 880/990 and they are very comfortable. They form a seal around your ear that is air tight. This causes you to hear your own voice, breathing, similar to IED's and with the bass ports closed you get a plunger effect that can be disconcerting if they are pushed or pulled as it moves your ear drum. They block outside sound quite well but pick up cable noise. IE touch the cable or any part of the headphone and you hear it loudly.
Headband: They went with a velcro enclosure using the micro hook and loop which is much thinner and doesn't fray like old style velcro. There is a conspicuous seam though where the two halves meet. It is softer than the button on one on my 990's and superior to the zip lock one on my 880's. The construction is identical to the 880 and 990 and I would be very surprised if the parts were not fully interchangeable.
Sound: Now for the bit you've been waiting for. Yeah they look nice and feel nice but how do they sound?
They sound constricted. I have other closed cans like the Sony MDRV6 and Sennheiser 428 but I never really noticed the tin can sound like I do with the C.O.P. Don't get me wrong, they sound fantastic but the sound stage is drasticly compressed compared to my open backed 990's and the way sound echos around inside the closed cans affects phasing which leads to a false sense of colored sound even though a sine wave sweeper shows these to be relatively flat.
The best way to describe the sound is that these are circum aural that sound like in ear entymotic headphones. And I'm pretty sure this is a result of the air tight seal from the ear pads. After I have broken them in some more I plan to put on some of the velour pads from my 990's to see if it improves the sound.
Over all I found the sound to be less linear than the 990 with a strong mid range (in spite of others reviews to the contrary) but a recessed upper to high range. This comes across as a bump around 2-3khz and a dip around 8-9khz which makes for smoother but less crisp highs. In my listening tests I had the 990's and COP's on my head and powered by the same FiiO amp so I could quickly swap back and forth and the difference in clarity, sizzle, and crispness was readily apparent. Some people find the 990's highs to be a little harsh so your mileage may vary and you may prefer the COP's recessed sound but I think the 990's are perfect headphones.
There is a serious bump in the 100-200hz range but because of the sound characteristics it doesn't appear very colored which makes it tolerable.
So what does the COP do better than any other Beyerdyamic? It has bass. Great heaping, slathered in gravy, towering above the mix, waves of bass. In the fully closed position the sound below 60hz pretty much drops off the face of the earth and they sound anemic not to mention that it strangles the drivers leading to a dead sound and no sound stage. At position 4 the infrasonics of these headphones are un-matched. They put Sony Xbass to shame. They make the Sennheiser 428's sound like your grandmas headphones. With sinegen I found the extension went all the way down to 15hz without much noticable drop in level. At 20hz these are clear and loud even at low volume.
Most bass type headphones sacrifice the over all sound in order to deliver good bass but not the COP. These may be the first bass maniac headphones I've ever heard that don't color the sound excessively and work just as well for classical or jazz.
A jack of all trades these are but master of none. While Jazz and classical are enjoyable, swapping back to my 990's was like pulling cotton out of my ears. The one exception is the acoustic bass used in jazz trios. The extension and infrasonics of these headphones let you hear every dusty note of the bass. I could feel the rosin flying off the string and floating in the air.
In position 4 the headphones also lose some of that tin can closed sound and start to open up. I think they would sound their best in position 4 with some attenuation of the bass with EQ to keep the open sound but flatten out the response.
Overall impression and critical listening:
Setup: Audioengine D1 into FiiO desktop amp. Fubar 320kbps MP3 and FLAC, COP at position 2.
Tracks: Dave Brubeck "Take Five" - Very good bass extension and an enjoyable sound. Suffers from recessed upper mids with the hi-hat chick being more muted, less cymbal sizzle, and less stick noise in percussion. Piano had a nice bottom end and sounded just as warm. Swapping over to my 990's was like pulling stuffing out of my ears and dialing the bass back.
...to be continued.