Excerpts from: Kent’s Mechanical Engineering Handbook
When direct noise, containing definite notes or harmonics, is transmitted along ducts or openings, it often is possible to eliminate objectionable harmonics completely by an acoustic filter that obstructs but little air flow or ventilation.
Sound filters are of two classes:
1) low-pass filters – which transmit low frequencies, but filter out higher ones; and
2) high-pass filters – which do the opposite.
A low-pass filter prevents transmission of the relatively high whistle often present in a ventilating duct. Low frequencies, predominant in explosive discharges, are filtered out by a high-pass filter, as an automotive muffler or Maxim silencer.
Continue reading Filtration of Sound
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