ACTIVE SOUND ELIMINATING DEVICE

摘要

PROBLEM TO BE SOLVED: To eliminate an exhaust sound which has a peak of sound pressure level in the primary to tertiary frequency sounds by interposing a resonance type sound elimination pipe on the upstream side of a sound adjusting pipe. SOLUTION: Exhaust after passing through a main pipe 1 passes through a resonance muffler pipe 5, a primary sound adjusting pipe 6, and a secondary sound adjusting pipe 7 together with noise and interferes with a sound from a branch pipe at the main/branch confluence part 2a of a branch pipe 2 to attenuate the noise, and is discharged from the terminal opening part of an exit pipe 3. A speaker unit SU controls the loudness of a sound for sound elimination generated by its internal speaker. A resonance chamber in a resonance type muffler pipe 5 provided annularly on the upstream side of the sound adjusting pipe 6 is so constituted that a second harmonic frequency (f2 =f1×2) sound included in the noise resonates. The primary and secondary pipes 6 and 7 are formed of sound absorbers such as glass wool and. absorb high-frequency sounds. Thus, the sound reaching the main/branch confluence part 2a of the branch pipe 2 has its higher harmonic sounds and second harmonic frequency sound attenuated and the noise of the remaining primary and third harmonic frequency sounds is attenuated with the low-frequency sound from the speaker unit SU.