The HDA 300 Audiometers Headphones from Sennheiser are designed for use with audiometers in aural-acoustic and educational applications, as well as by ear, nose, and throat doctors. They have 1/4", dual mono connectors for compatibility with a range of equipment. The headphones provide passive ambient noise attenuation, allowing the subject or patient to hear the tests without outside noise. 100 pairs of hygiene pads are included.