Hearing acuity experiments at AT&T in 1949. The test subject sits in an anechoic chamber in front of a high fidelity speaker. Sounds differing slightly in loudness and pitch are played, and she indicates which is louder by pressing a button in her hand. A tube in her ear canal conducts sound to a condenser microphone to monitor the intensity of sound actually reaching her eardrum. The subject and apparatus are supported on a metal screen in the center of the chamber, as a solid floor would disturb the sound patterns. The bass speaker at bottom is a folded horn speaker, with a multicell horn tweeter on top.