A second object of the present invention is that, by providing an acoustic wave generation means for generating an anti phase sound in the vicinity of upper side part of an exhaust outlet and providing a second pressure detector between the exhaust outlet and the acoustic wave generation means, a positive negative doublet sound source is constituted in {HEAD ~ a manner} having the exhaust outlet as a positive sound source and {TAIL ~ the acoustic generation} means as a negative sound source 
having
A second object of the present invention is that , by providing an acoustic wave generation means for generating an anti phase sound in the vicinity of upper side part of an exhaust outlet and providing a second pressure detector between the exhaust outlet and the acoustic wave generation means , a positive negative doublet sound source is constituted in { HEAD ~ a manner } having the exhaust outlet as a positive sound source and { TAIL ~ the acoustic generation } means as a negative sound source
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