Magnetic resonance imaging (MRI) devices generate loud acoustical noise during operation. The sound pressure level of the MRI noise depends on the imaging sequence, but it is generally 100 dB or more. Our current study is aimed at the improvement of the acoustical environment for the MRI patient by means of an active noise control system. We propose using a feedforward system because acoustical MRI noise typically comprises unsteady pulse waves. It is important for a feedforward system that the reference microphone is located near the sound source. Here, we discuss the measurement of the sound source of MRI acoustical noise to position a reference microphone and show the effect of reference microphone position in an active noise control system by computer simulation. The apparent source of MRI acoustical noise was estimated from the delay time of the cross correlation between the signals of two microphones on the table in the MRI gantry. The result indicates that the apparent source lies between the center and edge of the gantry. Computer simulation shows that the proposed system produces substantial noise reduction when the reference microphone is attached in the vicinity of the apparent origin of the sound, such as in the wall of the scanner.