Oregon Patent of the Month – July 2021
Many headphones come equipped with active noise cancellation, which plays an anti-noise signal through the speakers. This anti-noise signal is an approximation of the negative of the undesired noise signal that it’s blocking out. Microphones monitor the ambient noise in real-time, and the anti-noise signal is generated in response. These feedforward systems are a constant drain on the battery. Some improvements to this battery drain have been made using contact sensors which sense if the headphones are being worn or unused. When unused, they can discontinue the feedforward loop and preserve battery. Avnera Corp. has designed an Active Noise Cancelling (ANC) system that performs Off-Ear Detection (OED) simultaneously, reducing costs and extraneous components.
They have implemented a narrowband OED system within the ANC component. The OED tone is injected into an audio signal at a sub-audible frequency, unheard by the user. The tone is present when played into the user’s ear, but disappears when the headphone is removed. Feedback microphones detect this dissipation and register it as not in use. The same microphones are used in the feedforward loop of the ANC and contribute to the use of anti-noise signals to block out sound. By combining the OED and ANC systems together, it reduces the technology needed, simplifying the device and reducing the cost to manufacture.
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