Patent ID: 8571226

Claim:
A sound reproducing device having: a loudspeaker arranged to produce sound from an audio signal provided by an audio signal source; a microphone positioned to pick up ambient noise and generate a microphone signal comprising said noise; an ambient noise cancellation (ANC) system arranged to receive the microphone signal from said microphone and to generate anti-noise corresponding to the ambient noise in said microphone signal; and an automatic polarity adaptation (AAP) system arranged to monitor said ANC system and, when a decision criterion is fulfilled, to cause a switch in polarity for the generated anti-noise, wherein the generated anti-noise is added to said audio signal provided by said audio signal source to form a resulting audio signal which is fed to said loudspeaker, and wherein said AAP system is arranged to cause said switch in polarity for the generated anti-noise by reversing the polarity of said resulting audio signal; said AAP system comprising: control means coupled to monitor said ANC system; switch means coupled to be controllable by said control means and having an output coupled to said loudspeaker; and inverter means coupled to receive said resulting audio signal and having an output coupled to an input of said switch means, wherein the control means is arranged, when said decision criterion is fulfilled, to issue a command or control signal to said switch means to enable said switch means to reverse the polarity of said resulting audio signal and deliver it to said loudspeaker.