Sennheiser PXC 250 Active Noise Canceling Headphones - Sennheiser's folding, lightweight, closed-ear PXC 250 is designed to keep outside noises out and headphone sound in--perfect for use in busses and libraries alike. 

When engaged, NoiseGard active noise reduction drops steady-state low-frequency noise (from about 500 Hz and below) by 15 dB--which the human ear perceives as more than halving the noise--thus enhancing the clarity of your music. The noise reduction circuit requires 2 AAA batteries, but the headphones work fine without the circuit engaged.

Sennheiser's fold and flip design lets you turn the ear pieces 90 degrees and fold the headphones closed. Their ported design lets them move more air for greater bass response.