Wearable Audio Phase Inversion for Low-Leakage Listening
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Solution Overview
Problem
Wearable devices, such as head-mounted wearable devices (HMWDs), face the challenge of minimizing sound leakage to bystanders while allowing the user to hear audio output without being obtrusive, as existing technologies do not effectively reduce sound intelligibility or amplitude to the surrounding environment.
Innovation Solution
The implementation of acoustic units (AUs) in HMWDs that operate as acoustic dipoles below a specified inversion frequency and as acoustic quadrupoles above it, using an audio control module to drive transducers with phase-inverted signals, creating destructive interference and reducing sound leakage to bystanders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wearable devices provide audio output to the user, then the user can hear audio clearly, but sound leaks to bystanders causing disturbance and loss of privacy
Solution Approach 1:
The patent applies acoustic cancellation technology where a second speaker generates sound waves that are the inverse (180 degrees out of phase) of the sound from the first speaker. These inverse sound waves cancel out the leaked sound through destructive interference, converting the harmful sound leakage into beneficial silence for bystanders while maintaining audio clarity for the user through bone conduction transmission.
2Ease of operation
If traditional speakers are used in wearable devices, then audio can be played, but the sound is intelligible to bystanders reducing privacy
Solution Approach 1:
The patent introduces bone conduction as an intermediary transmission medium. Instead of directly radiating sound into the air where bystanders can hear it, the audio signal is transmitted through the bone structure of the skull, which acts as a mediator to deliver sound directly to the user's inner ear while bypassing the air conduction path that would allow bystanders to intercept the audio information.
3Reliability
If sound amplitude is increased for user hearing, then audio is clearer for the user, but disturbance to bystanders increases
Solution Approach 1:
The patent segments the audio transmission path into two separate channels: one for the user and one for the environment. The first speaker generates sound for user perception through bone conduction, while the second speaker generates inverse sound waves specifically targeted at canceling environmental sound leakage. This segmentation allows independent control of user audio quality and environmental noise cancellation, enabling high amplitude for user clarity without proportionally increasing bystander disturbance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows users to hear audio clearly while significantly reducing sound intelligibility and amplitude to bystanders, enhancing privacy and minimizing disturbance, without obstructing the user's ability to hear the ambient environment.
Implementation Method 1
operated as acoustic dipoles when presenting output below a specified inversion frequency and as acoustic quadrupoles when presenting output above the inversion frequency. The output above the inversion frequency is phase inverted, producing destructive interference.
Data Source
AI summary
A head-mounted wearable device (HMWD) provides audio output from a first speaker that is driven with a first signal and a second speaker that is driven with a second signal. Based on a volume level setting, an equalization profile and inversion frequency are determined. The equalization profile selectively amplifies or attenuates particular frequencies or ranges of frequencies. Those frequencies in the second signal that are above the inversion frequency have their amplitude inverted, relative to the first signal. When driven by the first signal and the second signal, the first speaker and the second speaker operate as acoustic dipoles below the inversion frequency and acoustic quadrupoles above the inversion frequency. Sound from the first and second speakers with frequencies above the inversion frequency exhibits destructive interference. As a result, the user wearing the HMWD is able hear audio output while audio amplitude perceived by the bystanders is significantly reduced.