Patent ID: 8494175

Claim:
A noise reduction device comprising: a noise sensor for sensing a noise; a controlling sound output section for generating a controlling sound based on a controlling sound signal, which controlling sound is to be superposed on the noise at a control center of a control space for reducing the noise; a noise controller for generating the controlling sound signal; and an error sound sensor for sensing an error sound between the noise and the controlling sound at the control center, wherein the noise controller includes an identification sound generator and an identification controller, wherein when an acoustic transmission function covering a path from the controlling sound output section to one of the error sound sensor and the noise sensor is identified by outputting an identification sound from the controlling sound output section and then by sensing the identification sound with the one of the error sound sensor and the noise sensor, the identification controller prompts the identification sound generator to generate the identification sound for identifying the acoustic transmission function provided that an ambient noise level sensed by the one of the error sound sensor and the noise sensor is not greater than a given threshold.