Acoustic coupling arrangements for noise-cancelling headphones and earphones
An active noise-reduction headphone arrangement has a housing bearing a loudspeaker having a first diaphragm surface coupled to a first volume of air bounded by and coupled to a user's ear, and a second diaphragm surface bounding a cavity within the housing assembly so as to define a second volume of air, rearward of the diaphragm; a conduit provided in the housing, the conduit being in fluid communication the ambient air via a first acoustic couple means having a first characteristic acoustic impedance, the conduit also being in fluid communication with said second volume of air via a second acoustic couple means having a second characteristic acoustic impedance; and a microphone having an inlet coupled acoustically to a predetermined location within the conduit.
1. An active noise-reduction headphone arrangement, comprising:
a housing bearing a loudspeaker for generating an audio signal, the loudspeaker comprising:
a first diaphragm surface coupled to a first volume of air bounded by and coupled to a user's ear; and
a second diaphragm surface bounding a cavity within the housing so as to define a second volume of air, rearward of the first diaphragm;
an acoustic potentiometer comprising:
a conduit provided in the housing;
a first port and a second port in the conduit, wherein the first port acoustically connects the conduit to ambient air and the second port acoustically connects the conduit to the second volume of air, such that the audio signal generated by the loudspeaker is acoustically coupled to said conduit, the second port being spaced apart from the first port; and
a microphone having an inlet coupled acoustically to a predetermined location within the conduit, the predetermined location of the inlet being spaced apart from the first port by a first length and from the second port by a second length, the predetermined location of said microphone within said conduit being selected to accurately control the magnitude of said audio signal to said microphone in accordance with a ratio of the first length and the second length.
2. The arrangement of claim 1 , wherein at least one of the first port and the second port has acoustic impedance properties primarily characteristic of an acoustic resistance.
3. The arrangement of claim 2 , wherein at least one of the first port and the second port is formed by sealing an overlying layer of resistive mesh material onto an opening having a predetermined surface area.
4. The arrangement of claim 2 , wherein at least one of the first port and the second port is formed by incorporating a material having a bulk acoustic resistance property into the conduit.
5. The arrangement of claim 1 , wherein at least one of the first port and the second port has acoustic impedance properties primarily characteristic of an acoustic inertance.
6. The arrangement of claim 1 , wherein at least one of the first port and the second port is formed by a tube, recess, or conduit or by radiation impedance coupled to said microphone.
7. The arrangement of claim 1 , wherein at least one of the first port and the second port comprises a plurality of openings arranged substantially symmetrically around a primary axis of the microphone.
8. The arrangement of claim 1 , wherein the arrangement operates simultaneously and in conjunction with a feedback-type ambient noise-reduction system.
9. The arrangement of claim 1 , wherein the arrangement operates simultaneously and in conjunction with both a feed-forward ANC system and a feedback ANC system.
10. An ambient noise-reduction system comprising:
an audio device selected from the group consisting of a headphone, an earphone and a cellular-phone handset; and
an active noise-reduction headphone arrangement incorporated with the audio device, wherein the active noise-reduction headphone arrangement comprises:
a housing bearing a loudspeaker comprising:
a first diaphragm surface coupled to a first volume of air bounded by and coupled to a user's ear; and
a second diaphragm surface bounding a cavity within the housing so as to define a second volume of air, rearward of the first diaphragm;
an acoustic potentiometer comprising:
a conduit provided in the housing:
a first port and a second port in the conduit, wherein the first port acoustically connects the conduit to ambient air and the second port acoustically connects the conduit to the second volume of air, such that the audio signal generated by the loudspeaker is acoustically coupled to said conduit, the second port being spaced apart from the first port; and
a microphone having an inlet coupled acoustically to a predetermined location within the conduit, the predetermined location of the inlet being spaced apart from the first port by a first length and from the second port by a second length, the predetermined location of said microphone within said conduit being selected to accurately control the magnitude of said audio signal to said microphone in accordance with a ratio of the first length and the second length.