Head-mounted active noise control system to achieve speech communication

In this paper, we propose a head-mounted active noise control (ANC) system with speech communication. Magnetic resonance imaging (MRI) device is one of medical equipment. Recently, MRI device is utilized for microwave coagulation therapy. However, MRI device generates a serious noise (over 100 dB SPL). Hence, surgeons and other medical staff are exposed to the large MR noise for many hours and cannot verbally communicate with each other. We have therefore proposed a head-mounted ANC system for reducing MR noise and realizing verbal communication under such a loud noise environment. However, MRI device is generally controlled by the operator outside the MRI room. Hence, speech communication between inside and outside the room is needed. We therefore integrate the speech communication function with the head-mounted ANC system. Concretely, the error microphones and secondary loudspeakers are also used as an interface to realize the speech communication. In this case, the outside voice may be returned through the error microphone, so an audio-integrated ANC system based on the echo cancellation is utilized. Linear prediction filter is also utilized for separating the inside voice from residual noise. In this paper, we demonstrate the validity of the proposed ANC system through some noise reduction experiments and subjective assessment tests on phoneme articulation.