The Sennheiser HD 660S2 are very good for neutral sound. They have a warm sound profile and, despite being open-back, pack more thump and rumble than their predecessor. Their exceptionally neutral mids also ensure that vocals and instruments sound natural and present. A dip in the low-treble hurts the clarity and detail of these sounds, while the following peak in the mid-treble makes sibilants sound more aggressive and piercing, comparatively. Their soundstage, which feels spacious and open, struggles to produce an out-of-head audio experience too, and you'll need an amp to power these over-ears. On the upside, they deliver bass and treble consistently across reseats.