I have tried the ATH-M20x, the ATH-M25 (an old discontinued model), the ATH-M30x, the ATH-M40x, and the ATH-M50 (the older version without the letter “x”), and I liked the ATH-M30x the most. Granted, everybody's ears and their sound preferences are slightly different, but to me, the M30x sound the best. While neither of the M-series headphones are perfectly “flat”, to my ears, the M30x sound the most balanced. My second favorite model is the M20x, which sounds very similar but cannot be folded for storage and does not come with a carrying bag. The comfort is best on the latter two models as well because they are the lightest out of the range and have a slightly softer earpad covering material when compared to the M40x and the M50, on which the imitation leather is thicker and not as pliable. Next, I am going to focus solely on the M30x. The construction of the M30x is time-tested and has proven itself durable. I did not notice any cosmetic or structural defects. The cable seems tough enough to survive daily use, but is soft and flexible enough to lay flat on the ground and be easy to coil. Since the headphones are light, and do not grip the head overly tightly, they are comfortable to wear for extended periods of time. The longest I have worn them without taking a single break was ten hours, and I did not experience any pain or discomfort. However, if the grip is still too tight for some, the headphones can be stretched around any object, be it a jar or a cardboard box, which is greater in width than the user's head, and left on it for a few days. The grip usually loosens up. The only criticism I have in terms of handling is that the size adjustment mechanism does not have any distinct size positions, nor even position markers, so you have to adjust it approximately, put the headphones on and correct the adjustment if needed, which can become especially annoying if the headphones are shared by two people with differently sized heads. To me, the Sony MDR-7506 size adjustment mechanism with numbered indentations is many times better. Happily, the sound quality of the ATH-M30x more than compensates for that shortcomming. Since neither of the frequencies stood out to me, I would say that the sound is well balanced. Even though the highs are very clear, sibilance is not a problem (for those who do not know, it is the annoying hissiness of the “s” sounds). The soundstage (or the size of the perceived space, in which the musicians appear to be playing) is quite large for closed-back-type headphones, and the imaging (or the ability to determine the position of each musician in that perceived space) is very impressive in this price range. For experiencing the clearest effect of that, Dolby Atmos is simply excellent! In short, if the lack of distinct size adjustment positions and a long, non-detachable cable is not an issue, I would highly recommend these headphones for either doing some studio work or just listening to your favorite tunes.