Loudspeaker Reaction Force Cancellation Using a Series Actuator

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Solution Overview

Problem

Loudspeakers experience undesirable reaction forces that degrade sound quality due to the vibrational reaction force transmitted via the mechanical coupling of the diaphragm and motor assembly, which are not effectively addressed by existing technologies.

Innovation Solution

A voltage-controlled current source is connected in series with the loudspeaker to drive an actuator that generates a force opposing the reaction force, using a sense resistor and power-controlled current source to provide a current proportional to the loudspeaker current, thereby canceling the reaction force.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a motor assembly is used to generate force on the diaphragm, then acoustic output is produced, but reaction force vibrations are generated that degrade sound quality

Engineering Contradiction:

Improveacoustic outputVSAvoidreaction force vibrations

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent applies the counterweight principle by introducing a second actuator that generates a force equal and opposite to the reaction force produced by the motor assembly. This secondary actuator effectively cancels the harmful reaction force vibrations, allowing the primary motor assembly to operate at full power without degrading sound quality through reaction forces.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Solution Approach 2:

The patent converts the harmful reaction force into a useful control signal. By sensing the reaction force and using it to drive the compensating actuator, the system transforms the problematic vibration into a beneficial cancellation mechanism, where the harmful effect becomes the basis for its own elimination.

Inventive Principle:

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

2Object-affected harmful factors

If an actuator is added to counteract reaction forces, then sound quality is improved, but device complexity increases

Engineering Contradiction:

Improvereaction force vibrationsVSAvoidsystem structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent merges the compensating actuator with the existing motor assembly structure, integrating the reaction force cancellation function into the overall loudspeaker system. By sharing mechanical components and using a unified control architecture, the system reduces the net increase in complexity while achieving vibration cancellation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces a sense resistor as an intermediary element that measures the reaction force without adding significant complexity. This simple sensing component provides the necessary feedback signal to drive the compensating actuator, serving as a low-complexity mediator between the motor assembly and the cancellation mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If a voltage-controlled current source is used to drive the actuator, then reaction force cancellation is achieved, but manufacturing complexity increases

Engineering Contradiction:

Improvereaction force vibrationsVSAvoidassembly process

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent implements a self-service control system where the sense resistor automatically provides the control signal for the voltage-controlled current source based on the actual reaction force being generated. This self-regulating mechanism eliminates the need for complex external control circuits or manual tuning, simplifying the manufacturing process while maintaining effective reaction force cancellation.

Inventive Principle:

Principle #25Self-service

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 method effectively reduces reaction forces, improving sound quality by counteracting the undesirable vibrations caused by the reaction force, suitable for various loudspeaker configurations without requiring extensive tuning adjustments.

Implementation Method 1

A motor of a loudspeaker creates an acoustic force on a diaphragm... An actuator is connected to a loudspeaker in a manner that the actuator creates an actuator force on a mass

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

measuring, using a current sense resistance connected in series to the loudspeaker, the current through the loudspeaker

Methodology Applied

Scientific EffectElectrical resistance: Electrical Resistance

Data Source

PatentUS12445773B2Method and apparatus for reducing reaction forces in loudspeakers

Publication Date: 2025.10.14 BAREFOOT SOUND LLC

AI summary

A method and apparatus are provided for reducing reaction forces in loudspeakers. The method includes providing, from a power source (312) connected to a loudspeaker (304), a current to the loudspeaker. The method also includes measuring, using a current sense resistance (308) connected in series to the loudspeaker, the current through the loudspeaker. The method further includes providing, using a voltage-controlled source (310) connected in series to the loudspeaker, a current substantially proportional to the measured current through the loudspeaker to an actuator (306), wherein the actuator is connected in series to the loudspeaker.