Noise suppressor, electronic apparatus, and noise suppression characteristic control method

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;
• and
• an air chamber enclosed by said reflection plate and a wall part above said reflection plate,
• 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 reflection plate comprises a configuration for allowing installation in and removal from said wall part, and
• wherein a resonance frequency of said resonator sound absorber is adjusted by stacking another reflection plate having the same through-hole characteristics as said reflection plate on said reflection plate.