Explanation: I realize that this will be of very little interest to most Head-fiers. Most probably have no reason to ever consider the M over the regular DT770 models, and in fact a good number probably haven't even heard of them. But that is not my reason for writing this review. Quite simply, there is not very much information about these headphones out there on this, our world wide web, a situation which I hope to alleviate in whatever small way I can. I bought these more or less blindly, and so I would like to share my experiences in case anybody else ever finds themselves in the same situation.
Background: Not very long ago, I learned that I am prone to earwax buildup, a problem which is exacerbated by frequent use of earplugs or IEMs. Being a drummer I require the use of both quite often, and so I began to search for an alternative. I needed something that could isolate as well as, or at the very least close to as well as a pair of earplugs, and it had to be something that didn't require me to stick it inside my ears. Of the limited options I was able to discover, the Beyerdynamic DT770M seemed like the best I was likely to find, so I placed an order.
Description: The Beyerdynamic DT770M is an alternate version of the popular DT770, with supposedly strong isolation for use by drummers or monitoring in noisy environments. Physically, it is the same as the other DT770s, only with pleather earpads, and an in-line volume control. Concerning the pads, they are much shallower than the normal velour ones. My ears pressed up right against the drivers, and I noticed that it got hot and sweaty in there pretty quickly. Build quality is good, exactly the same as you'd expect from any other DT770, only the in-line volume control seemed unnecessarily bulky, and was made of cheap and flimsily put together plastic. The DT770M has an 80 ohm impedance and 105 dB sensitivity, so it's not too hard to drive. It worked ok with my portable player.
Functionality: Beyerdynamic claims that the DT770M have a noise attenuation of 35 dB. That's higher than the quoted attenuation of many earplugs, and matches the lower range of what Etymotic claims for their IEMs. Well, it is an outright lie. Either that or it's an intentionally misleading spec based on a meaninglessly high frequency. While playing drums, I compared them to Ety mc5s and some regular foam earplugs. I wouldn't even say the DT770M isolated half as well as either. In fact, they didn't really isolate better than any other typical set of closed headphones, which is to say they are completely useless for the drumming or monitoring purposes they were intended for. Is it possible I just didn't get a good seal? Perhaps, but quite frankly I don't see how. They fit very snugly on my head, and I have pretty small ears which had no problems getting a circumaural fit inside the cups. There are some reviews on retail sites where people claim they have excellent isolation as advertised, but I'm not sure I believe in those peoples' credibility. I've known many drummers and musicians over the years, and I'm one of the only ones I know who takes even the slightest precautions to protect their hearing. (Yet I'm the one with ear troubles. Thanks irony!) The DT770M might seem like they isolate some if you've never worn earplugs before and you are blasting music through them. Of course, I could just be crazy.
Sound: But what about the sound? They are DT770s after all. How does it compare to the regular versions? It doesn't. Unfortunately, whatever it is that they did inside the cups to try and make them more isolating killed the drivers. There is absolutely no extension in either the bass or treble, and I don't mean just deep sub-bass or really high treble. I mean even the bass or treble you would expect from an already rolled off headphone is missing. Grados would be bass monsters in comparison. All that's left are some mids, and what's there is extremely muddy, smeared, and compressed. If I had to describe them in two words, those words would be "Immanently Unlistenable." A $20 pair of earbuds from Walmart would probably be a big improvement over these, and they cost $200! I know that they were meant for more utilitarian purposes and high fidelity sound isn't their main selling point, but for crying out loud!
Conclusion: So all in all, the DT770M fail miserably in every way. They don't even partially fulfill their main purpose which is isolation, and on top of that they are probably the worst sounding headphones I've ever heard. They don't even deserve to be used as a paperweight. Thankfully I was able to return them right away.
Edited by manveru - 7/29/12 at 1:59pm