If you do decide to take the Sennheiser HD 558 out with you, passers-by will be able to hear what you're listening to as they're open-backed headphones. The perforated back grille of each cup leaks sound, and also means that they provide very little isolation from the noise of the outside world. They're next-to useless on public transport, unless your aim is to annoy your fellow passengers.
As an at-home pair though, they're utterly brilliant. With a detailed, smooth and balanced sound, they can take on all genres of music and delight the ear. They trade away some of the bass thickness of the cheaper HD 518 set, but in return provide superior separation and dynamics, and a more robust mid-range. Complicated musical arrangements remain coherent, and this stepping-away from a more low-end focused approach makes even better use of the airiness offered by an open-back design. The treble is detailed and refined, only the bass could do with a bit of a tightening-up.
To get better sound within Sennheiser's HD range, you'll have to step up to the HD 600/650 - which cost at least twice the price. With them will come more musicality and greater dynamics, but that's not to suggest the HD 558 won't satisfy discerning ears.
These lower-end 5** models also use lower-impedance 50Ohm drivers, as opposed to the 300Ohm 6-series models, lessening the need for a dedicated headphone amplifier. A good amplifier can still improve the sound - our test valve amp added a little low-end power - but these cheaper headphones are a great choice if you want to keep your setup simple, and affordable.
Clarity fiends may want to consider the AKG K271 MKII, and bassheads something like the Ultrasone HFI-680, but as an all-rounder that can accommodate virtually all tastes, the Sennheiser HD 558 are very tough to beat at the price. Their fairly neutral sound can skip between rock and classical tracks without a slip, and also makes them an excellent choice for sticking into a television or receiver for late-night TV or movie-watching.
The Sennheiser HD 558 are an excellent entry point into high-end audio. Detailed, refined and smooth-sounding, they never offend the ear and don't spend any time on surface level details like the HD 598. They skip between genres, and between music, movies and TV, with ease, and are supremely comfortable to wear.