Patent ID: 8295503

Claim:
A noise reduction device, comprising: a housing comprising an acoustic wave filter comprising a cavity formed by a plurality of sidewalls, and a plurality of ducts having at least one outer duct and at least one inner duct, each of the ducts being connected to the sidewall of the cavity for transmitting an acoustic signal including a noise signal into/out of the cavity; a speaker connected to the cavity; and a microphone arranged between the speaker and a human ear canal, and configured to simultaneously channel with the cavity and the at least one outer duct; a noise reduction circuit configured to receive the acoustic signal including the noise signal and generating an electrical signal; and a plug connected to the housing through the at least one inner duct, and configured to be tightly fitted inside the human ear canal and to prevent noise from entering the human ear canal, wherein the microphone is configured to receive the acoustic signal inside the cavity, convert the received acoustic signal into another electrical signal and transmit the electrical signal to the noise reduction circuit; wherein the speaker is configured to receive the electrical signal generated by the noise reduction circuit, use the received electrical signal to generate an out of phase acoustic signal accordingly, and feed the out of phase acoustic signal into the cavity to interfere with the noise signal inside the cavity, so as to reduce the noise signal inside the cavity, and wherein the acoustic wave filter is configured to reduce high-frequency range noises while the noise reduction circuit is configured to reduce low-frequency range noises.