Billed as audiophile-grade noise-cancelling headphones for use during travel, Sennheiser's new PXC450 Headphones ($450) feature NoiseGard 2.0, which is an "active noise compensation" technology that promises to reduce ambient noise by up to 90%. New to the system is a set of optimized noise filters, processors, and microphones (plural) to sample and cancel outside noise; Sennheiser builds in volume controls and a "talk through" button that lets you…
