These are good headphones for blocking external sound.

Model EX-29       Specifications    
TYPE: Dynamic closed back SPEAKERS within a Closed Back Isolation Chamber.
FREQUENCY RESPONSE: 20 - 20,000 Hz
DRIVERS: 40 mm    
IMPEDANCE: 32 ohms
SENSITIVITY: 114 db at 1000 Hz.    
CORD: 9 feet    
PLUG: stereo 3.5mm w/gold plated 1/4" adapter    
INPUT POWER: 500 mW    
SOUND ATTENUATION AVERAGE: 29 dB    
WEIGHT: 11.5 oz.