Pros: Good sound, bests Bose at active cancellation and sound.
Cons: Pricey. Better sound quality available for the price
Having spent time with a lot of Bose QuietComfort (X) headphones on my ears, they all left me wanting better sound. I work in a noisy newsroom. The need for cutting back some of the chatter is always a premium here. Active cancellation was the first stop on the path that led me to in-ear customs.
Style File: The Sennies are pretty attractive, as far as headphones go. Nice mesh case, and the cups are rather large (appreciated all the more after spending time with Bose). Sennheiser did a great job on comfort. You can wear these a long time without fatigue. If the thinking is-- gotta be comfy through an 8-hour flight, then mission accomplished.
Cancellation: Well this is the big headline, and the reason most will be buying them. If you're all about cancellation, spend the extra cash for good customs. They do a better job at passive cancellations than the actives ever will. I can still hear a lot of the world around me in active monitors, though it is muted. Simple on-off comparisons confirm the headphones do their job, and to my ear, produce an overall quieter effect than the Bose.
Sorry to report, the sound quality out of the 450s is only average. Decent but not extended bass, stronger through the mids and a precipitous falloff on the high end. There's very little soundstage to be impressed by. I own little to compare them with, and will amend once my 650's arrive. I'm expecting this pair to pretty much take it on the chin. They don't sound 'bad' per se, but they don't 'wow' in any area, either. I get more of a lift out of my Bowers & Wilkins P5's, which at least show some character and can provide entertainment much as a comfy old pair of slippers will on a cold night.
My use for this pair are as a relief pitcher at work, if I need a break from my in-ears. They serve that need, but they are definitely not the first pair of cans I reach for.
Final Thoughts: If you're a slave to active technology, these are as good as it gets. The only other pair that did cancellation this well were my old Sony in-ear buds, but the Sennies blow the Sonys away in sound quality. If I were looking for the best active canceling cans, I'd say look no further. But you can find better sound for the money.