Patent ID: 8127886

Claim:
A noise suppression characteristics adjustment method, comprising: adjusting noise suppression characteristics of a noise suppressor, said noise suppressor comprising: a muffler comprising a reflection plate for reflecting sound from said cooling fan, said reflection plate being provided at a position in said cooling duct confronting an intake plane of said cooling fan and formed substantially parallel to the intake plane, wherein a sound-absorbing part of said muffler is provided on said reflection plate, wherein a distance d between said reflection plate and said intake plane is set such that d<c/(2×f) where f is a sound-absorption frequency of said muffler and c is a speed of sound, wherein said muffler is located inside said cooling duct, wherein a through-hole is provided in said reflection plate, wherein said through hole comprises a plurality of through-holes, and wherein a resonance frequency of said resonator sound absorber is adjusted by blocking at least one of said plurality of through-holes.