Patent ID: 8682001

Claim:
An active noise reduction (ANR) earphone, comprising: an acoustic driver configured to deliver acoustic energy into a front cavity, the front cavity including a first volume of space inside the earphone and into which the acoustic driver delivers the acoustic energy, a second volume of space inside the ear canal of a user, and a nozzle section coupling the first and second volumes; a tip for coupling the earphone to the ear of the user, the tip including at least a portion of the nozzle section coupling the first volume of the front cavity to the second volume of the front cavity; and active noise reduction circuitry comprising a feedback microphone acoustically coupled to the first volume of the front cavity, for detecting noise in the front cavity; feedback circuitry responsive to the feedback microphone for providing a feedback noise cancelling audio signal into the front cavity; a feed-forward microphone acoustically coupled to ambient space outside the housing; feed-forward circuitry responsive to the feed-forward microphone for providing a feed-forward noise canceling audio signal into the front cavity; and wherein the acoustic driver is configured to transduce an output noise canceling audio signal comprising the feedback noise canceling audio signal and the feed-forward noise canceling audio signal into acoustic energy; wherein the nozzle is oriented and shaped to control the acoustic impedance of the nozzle, such that at least one of the cross-sectional area of the nozzle, the ratio of the nozzle length to the nozzle cross sectional area, or the acoustic mass of the nozzle causes the impedance of the nozzle to be below a threshold that varies over the operating range of the active noise reduction circuitry.