Koss has produced a very interesting headphone here. It does not sound like any other I've listened to, which is not necessarily a bad thing.
First off, the treble energy is very recessed and laid back for a headphone claiming to be a hifi can. The tonal balance here is very dark. I would guesstimate that these cans are down at least 12dB at 10Khz compared to my reference headphones, the AKG K701. It does not appear to be a limitation of the driver but rather a deliberate design choice by Koss in the voicing of this product. Impressively it does not hold back these cans as much as you might think in areas such as high frequency detail retrieval and soundstage/imaging. Cymbals sound crisp and well defined with good air and separation for a closed back can in this price range, the sound is just rather recessed and muted. It results in a very mellow sound that places strong emphasis on the lower midrange and male vocals. There is definitely no risk of listening fatigue or sibilance/harshness on these cans. They fare surprisingly well with classical music, something I was not expecting considering the lack of treble energy.
The midrange is again mellow and offers good detail retrieval and dynamics for this price, but it is definitely not a reference or flat sound. They are very colored, and whether you find this to your liking or not will be hard to say. I personally find that it depends upon the vocals in the song being listened to. The midrange on these Koss flatter most male vocals (with a couple of exceptions), but tend to leave female vocals recessed and flat sounding. They tend to emphasize texture and chord movement within the frequencies they are exaggerating, so certain male solo performances come out with a very engaging and enjoyable performance, if not a realistic sounding one. If you are a stickler for accuracy these cans will not be to your liking, but their colorations make certain types of music quite enjoyable to listen to in my opinion.
Bass is strong, a bit too strong in the 100-200 Hz region, most likely made worse by internal resonance from the closed back design. Leading edges are detectable in most music, though the drivers seem to struggle to retrieve micro dynamics and other detail in the lower frequencies when things get very busy. They do alright for the price Amazon sells them for. Solo drum lines are taut and crisp with good punch for a phone in this price class. They also offer good weight to bass attack, though sometimes they sound a bit soupy and heavy if the primary frequency of the bass line is around or above 100Hz. Detail aside, the bass response itself is pretty fast and tight when driven by a quality amp. On a DAP or cheap receiver the bass is heavy, sloppy and dominates the musical presentation. They feel reasonably flat down to perhaps 40Hz and taper off sharply below that, but they will hit hard and pretty deep if that is what you are looking for.
Soundstage and imaging are, considering my comments about the treble response, impressive. One would expect the sound to be stuffy and closed-in, but instrument separation is remarkably good for the tonal balance present. Instruments are often present considerably "outside the head" when called for by the recording, though they offer overall a pretty intimate "in your head" listening experience like you'd expect from a closed back headphone design. Still, there is good ambiance and a full headstage befitting a proper hifi can when listening to the right recording.
Build quality is fair, not great. They appear to be made of metal from the picture. They are not. It is all painted plastic. Nothing feels flimsy per se, but I wonder how long the folding hinges will hold up over years of use. Comfort is a mixed bag. The headband is very comfortable, more so than my K701 in fact, but there is enough clamping force that the cups tend to irritate pressure points around your jaw over time. Worse is the matter of your ears getting hot and sweaty over long listening periods. In a warm room I can't make it more than 30 minutes before my ears are too hot to be comfortable anymore, and moisture condensation builds up on the plastic guard covering the drivers quite easily. I've actually wiped full drops off of them before, and this condensation must be getting to the drivers as well. I've thought of asking Koss directly if this presents a reliability concern for them, but Koss has been making closed cans with this type of rubber cup design for decades, so they must know what they're doing. The cups themselves seal around your ear quite securely, and block a great deal of ambient noise. The sound is affected noticeably by how you position them on your ears. I found that sliding them up and back until the front tips of my ears touch the edges of the cup, then centering them slightly after that produced the best tonal balance.
Overall, I am pleased with the performance they offer for the price paid. These are a very laid back sounding can and those seeking a high energy headphone with a "sparkle" or attack in it's treble should immediately look elsewhere. I would describe them as neither warm nor cold sounding, just very mellow with treble energy pushed to the back of the presentation. The midrange is never harsh and offers a colored but detailed and often very enjoyable listening experience with powerful bass to back it up. I bought these knowing their reputation for recessed treble energy and find that, for certain types of music, they present exactly the relaxing laid back sound I was looking for. You will not be getting listening fatigue with these headphones, that much is certain. I don't know if they would be worth their full retail price, but for the price they are selling at I think their performance is worthy purely on a technical level. So long as you understand their dark tonal presentation and the fact that they were clearly never intended to sound accurate (non-fatiguing being the motive) the MV1 proves to be an enjoyable headphone and a decent value within it's class.
Final note: For those who worry about break-in, I found that their sound changed mildly over the course of their first 100 hours of use. The treble opened up slightly and the bass/lower-mids leaned out a bit. This was a welcome and much needed change, as they simply sounded too dark when they were new. Quality of amplification matters too, as I've found they scale reasonably well with better amps. They would clearly pair well with a bright sounding solid state amp, but my slightly warm sounding Channel Islands VHP2 coaxes dynamics and details out of them that cheaper amps could not despite having a sonic signature that makes them sound even darker.