Force-Cancelling Isobaric Audio System for Wearables
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Solution Overview
Problem
Existing speakers mounted on wearable devices, such as AR glasses or VR headsets, generate vibrations that cause unwanted shaking and contamination of inertial measurement unit (IMU) signals, leading to inaccurate motion tracking. Additionally, these speakers often suffer from audio leakage, compromising user privacy, and struggle with bass performance due to increased shaking and leakage.
Innovation Solution
A force-cancelling audio system utilizing speakers with a shared isobaric back volume, where speakers move in opposing directions to cancel force transmission into the enclosure. This configuration includes matched front waveguides for dipole or linear quadrupole sound wave radiation patterns, allowing for adjustable polar patterns and improved bass performance by reducing low frequency cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If speakers are mounted on wearable devices to provide audio output, then audio functionality is improved, but vibrations are generated that cause unwanted shaking and contamination of IMU signals
Solution Approach 1:
The patent employs force-cancelling speakers that move in opposite phases to counterbalance the vibrations generated by conventional speakers. The second speaker is driven with inverted polarity relative to the first speaker, creating equal and opposite forces that cancel each other out, thereby eliminating the unwanted shaking and IMU contamination while maintaining audio functionality.
Solution Approach 2:
The patent converts the harmful vibrations generated by speakers into a beneficial force-cancelling mechanism. By intentionally generating opposite-phase vibrations through the second speaker, the system transforms the harmful mechanical vibrations into a useful counterbalancing force that eliminates the very vibrations they were meant to reduce.
2Ease of operation
If speakers are mounted on wearable devices to provide audio output, then audio functionality is improved, but audio leakage occurs that compromises user privacy
Solution Approach 1:
The force-cancelling mechanism reduces overall acoustic radiation by equalizing and opposite-phase vibrations from multiple speakers. This creates a null-field effect where the acoustic energy that would normally radiate outward is instead canceled through destructive interference, thereby reducing audio leakage while preserving the intended audio output to the user.
3Ease of operation
If speakers are mounted on wearable devices, then audio output is provided, but bass performance deteriorates due to increased shaking and leakage
Solution Approach 1:
The force-cancelling speakers specifically address bass frequency vibrations by generating opposite-phase forces that counterbalance the low-frequency oscillations. This eliminates the shaking and acoustic leakage that normally degrade bass performance, allowing the system to maintain reliable bass output without the unwanted side effects.
4Device complexity
If a single enclosed speaker is used, then device complexity is reduced, but force cancellation capability is limited
Solution Approach 1:
The patent combines multiple speakers within a shared enclosure space, allowing them to operate as a coordinated force-cancelling system. The first and second speakers share the same enclosure and back volume, enabling them to generate and cancel forces collectively while maintaining a relatively simple overall structure compared to distributed multi-speaker systems.
Solution Approach 2:
The shared enclosure and back volume serve multiple functions: they house the speakers, provide acoustic coupling between drivers, enable force cancellation through shared vibration cancellation, and support the acoustic seal. This multi-functionality reduces the need for separate components and maintains device simplicity while achieving force cancellation.
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
The isobaric audio system effectively reduces audio leakage, enhancing user privacy and maintaining accurate IMU signal tracking by minimizing vibrations. It also achieves improved bass performance by allowing for deliberate mismatch between speakers to enhance low frequency output.
Implementation Method 1
A controller of the audio system is configured to drive the plurality of membranes... providing a driving current through the voice coils... such that the plurality of membranes generates sound
Implementation Method 2
the plurality of membranes generates sound that is output from the plurality of ports to form a first sound wave radiation pattern
Data Source
AI summary
An audio system comprises a plurality of membranes within an enclosure. A first surface of each membrane is part of a shared back volume within the enclosure and pressure within the shared back volume is configured to be isobaric. A second surface of each membrane is part of a front volume within the enclosure that includes a plurality of ports. A controller of the audio system is configured to drive the plurality of membranes. In a mode of operation, the controller is configured to match audio output between the plurality of ports, forming pressure waves of equal amplitude and opposite phase and generating a substantially dipole or linear quadrupole sound wave radiation pattern for frequencies above a predefined threshold and mismatch audio output between the plurality of ports for frequencies at or below the predefined threshold to generate a substantially monopole or cardioid sound wave radiation pattern.