Logitech rates the coverage area at 30 feet. I gave that a test at home and the office, leaving my iPod at various spots and wandering around. The sound quality did not change at all until I reached the edge of coverage, several steps beyond 30 feet in most cases. I did not encounter any interference from other devices, and the number/thickness of walls in between the iPod and me didn’t seem to break up the signal.
When I did reach the end of its effective range, the headphones bowed out gracefully. Rather than turning into a mess of static or even losing some clarity, they simply cut in and out cleanly. It was almost like the lobby lights being dimmed minutes before the symphony is about to start – a polite reminder to move closer to the transmitter. Much better than a jarble of music and interference in my ears.