PROBLEM TO BE SOLVED: To provide a noise reduction system capable of reducing hammering noise repeatedly generated.SOLUTION: The noise reduction system for reducing noise including hammering noise emitted from an MRI apparatus, being repeatedly generated, includes: error signal generation means 10 for generating an error signal e on the basis of the detected noise； estimation noise generation means 22 for generating an estimation noise signal d' indicating an estimation value of an acoustic pressure of the noise on the basis of the error signal e and a fist control signal z to cancel the noise； delay signal generation means 24 having a time delay property D corresponding to a time interval in which the hammering noise is generated, for generating a delay signal r from the estimation noise signal d'； a control filter 21 for generating a first control signal u from the delay signal r； and a speaker unit 30 including at least one pair of a first filter generating a second control signal from the first control signal u and a control speaker outputting a control sound by converting the second control signal into a sonic wave and including transmission means for transmitting the control sound.SELECTED DRAWING: Figure 1【課題】繰り返し発生する打撃騒音を低減できる騒音低減システムを提供する。【解決手段】ＭＲＩ装置から発せられた、繰り返し発生する打撃騒音を含む騒音を低減する騒音低減システムであって、検出した騒音に基づいて誤差信号ｅを生成する誤差信号生成手段１０と、誤差信号ｅと騒音を打ち消すための第１の制御信号ｚとに基づいて、騒音の音圧の推定値を示す推定騒音信号ｄ’を生成する推定騒音生成手段２２と、打撃騒音が発生する時間間隔に対応する時間遅れ特性Ｄを有し、推定騒音信号ｄ’から遅延信号ｒを生成する遅延信号生成手段２４と、遅延信号ｒから第１の制御信号ｕを生成する制御フィルタ２１と、第１の制御信号ｕから第２の制御信号を生成する第１のフィルタと第２の制御信号を音波に変換して制御音を出力する制御スピーカとの組を少なくとも１組と、制御音を伝達する伝達手段と、を含むスピーカユニット３０とを具備する。【選択図】図１
