Speaker Force Cancellation via Motor Assembly Counterweight

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Solution Overview

Problem

Speakers mounted on wearable devices, such as VR headsets, generate vibrations that cause unwanted shaking and contamination of inertial measurement unit signals, leading to inaccurate measurements and audio leakage, which is undesirable for wearable device applications.

Innovation Solution

A speaker system with a single driver that utilizes a non-rigid suspension and a decoupling spring to couple the motor assembly to the fixed frame, absorbing magnetic forces and canceling out vibrations, thereby reducing contamination and audio leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a speaker with single driver is used in a wearable device, then the device structure is simplified and cost is reduced, but vibration and shaking are generated causing contamination to IMU signals

Engineering Contradiction:

Improvespeaker structureVSAvoidIMU signal accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The speaker system is segmented into two independent moving masses: the first moving mass (diaphragm, voice coil, surround) that generates sound, and the second moving mass (motor assembly) that generates opposing force. This segmentation allows each mass to be optimized for its specific function while working together to cancel vibrations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The motor assembly acts as a counterweight that generates force equal and opposite to the force generated by the diaphragm. By tuning the motor assembly mass and suspension stiffness, the system creates anti-phase vibrations that cancel out the harmful vibrations transmitted to the wearable device frame and IMU sensors.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

2Device complexity

If a speaker with single driver is used in a wearable device, then the device structure is simplified, but audio leakage occurs compromising user privacy

Engineering Contradiction:

Improvespeaker structureVSAvoidaudio leakage

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The motor assembly generates acoustic radiation pressure that is equal and opposite to the diaphragm's acoustic radiation. This counteracting force cancels the sound waves radiating from the speaker, preventing audio leakage while the single driver structure maintains simplicity.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Solution Approach 2:

The motor assembly, which normally generates unwanted vibrations and heat, is repurposed to generate beneficial counteracting acoustic radiation pressure. The harmful side effect of motor assembly movement is converted into a useful force that cancels audio leakage and improves privacy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If better bass performance is achieved in speakers, then low frequency response is improved, but shaking and vibration increase making the speaker unsuitable for wearable devices

Engineering Contradiction:

Improvebass performanceVSAvoidshaking and vibration

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The motor assembly is tuned to generate equal and opposite force to the diaphragm's bass-generating movements. This allows the diaphragm to produce strong bass frequencies while the motor assembly simultaneously generates counteracting force that prevents the vibrations from being transmitted to the wearable device structure.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Solution Approach 2:

The system uses dynamic force cancellation where the motor assembly and diaphragm are tuned to operate at the same natural frequency. This dynamic coordination allows the system to maintain bass performance across varying frequencies while continuously canceling vibrations through the opposing forces generated by the two moving masses.

Inventive Principle:

Principle #15Dynamics

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 solution effectively mitigates vibrations and audio leakage, maintaining accurate inertial measurements and ensuring privacy by achieving significant attenuation of reaction forces and displacement, while maintaining acoustic output.

Implementation Method 1

Methodology Applied

Scientific EffectMagnetic forces: Lorentz Force

Implementation Method 2

Methodology Applied

Scientific EffectVibration damping: Damping

Data Source

PatentUS20240292136A1Speaker with Single Driver Force Cancellation

Publication Date: 2024.08.29 META PLATFORMS TECHNOLOGIES LLC

AI summary

A speaker system can include a first moving mass, such as a diaphragm, coupled to a fixed frame via a first non-rigid suspension and coupled to a voice coil. The speaker system can include a second moving mass, such as a motor assembly, coupled to the fixed frame. The speaker system can include a passive radiator coupled to the fixed frame via a second non-rigid suspension. The motor assembly and the diaphragm are configured to move in response to an audio drive signal, causing a pressure to be generated and a first force to be generated on the fixed frame. The fixed frame is configured so that the pressure is shunted to the first passive radiator that is configured to generate a second force in response to the shunted pressure causing a second force on the fixed frame that cancels at least a portion of the first force.