When Sony introduced its Altus MDR-777LP headphones, the company touted the "80KHz frequency response" along with a couple of other unique features. First off, that number doesn't mean a single thing without some sort of qualifier like "plus or minus N decibels." But marketing speak aside, the Altus is a pretty good set of full-size cans for $150. These headphones compete squarely with other closed-back circumaural headphones like the Bose TriPort. The Altus trumps the TriPort in some ways, while the TriPort wins out in others, so it comes down to personal preference.
The Altus's brushed-aluminum and plastic earcups are on hinges, so they fold up into the well-padded headband and fit nicely inside the included soft carrying bag. The adjustable mechanism is far more substantial and sturdy than the sliders on the TriPorts. The cabling is one-sided, coming out of the bottom of the right earcup; this can be a plus if you move around a lot and have a tendency to get "Y" headphone cables caught on things.
The earcups are rimmed with large, soft leather oval pads; I had to jockey the phones a little bit to get them to fit all the way around my radar dishes, but they provide a comfortable fit in general. After about 45 minutes of listening, though, the outer edges of my ears hurt because the cups aren't quite as deep as those of the TriPorts. In fact, the TriPorts and the Sennheiser HD 555 both win out in the comfort department.
One of the Altus' unique features is a switch on each earcup that keeps the diaphragm inside the headphones in a fixed position, blocking out roughly as much noise as a good closed-back headphone like the TriPort. Flip the switches, and the diaphragm can move freely, letting in a bit more sound from the outside world. The difference is subtle but perceptible--maybe a change of 5 or 6 dB--but setting the switches to Open doesn't make the Altus sound like open-backed headphones, so you don't get the spacious sound you get from, say, Grado headphones.
Many types of music benefit from the Altus' "forward" midrangey sound, especially intimate tracks like Ella Fitzgerald and Joe Pass vocal and guitar duets. On big band tracks (think Count Basie or the Mingus Big Band), the midrange can be a bit on the strident side, particularly after listening to the much more laidback mids of headphones like the TriPorts. However, the Altus headphones give you decent stereo imaging for headphones at this price (and without using a dedicated headphone amplifier), which is especially noticeable when you're watching action movies like The Fifth Element. (Notably missing from the package is a quarter-inch adapter for listening on home stereo equipment.)
The bass is present but not as powerful as with the Bose cans--or even as powerful as many of Sony's in-ear headphones. R&B and hip-hop tracks sound full and aggressive without getting muddy on the bottom, though a bit more punch would have been nice for definition. The highs don't sparkle, but they're not washed out either; hi-hat and ride cymbals are very clear if not quite as lively as with the TriPorts.
The Altus' "80KHz frequency response" refers to its ability to reproduce sounds beyond what we can actually hear. While Sony doesn't give any information about how much power those ultra-high sounds have, it does indicate that Sony is trying to appeal to the burgeoning wannabe audiophile market. They even designed the Altus headphones with drivers that are parallel to the human ear, supposedly delivering a more natural sound. Of course, any benefits will depend strongly on your source material. For example, if you're listening to compressed music, you're losing much of the highs in the music--as well as stereo imaging--that these headphones are ostensibly able to reproduce.
Overall, these are nice cans for $150, and the adjustable passive noise blocking is a unique and interesting feature. The sound quality is different from that of the Bose TriPorts, and your choice should depend largely on whether you prefer beefy bass and sparkly highs or a more midrangey overall sound. There are better-sounding cans at this price, including open-backed models like the Grado SR125 and the Sennheiser HD 555, but those won't give you the passive noise blocking of the Altus, which is why the latter makes a better travel companion on the whole.