Loudspeaker Doppler Distortion Cancellation via Feedback Coil

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The Doppler effect causes unwanted distortion in audio loudspeakers, particularly in small devices lacking crossover circuitry, leading to complex pitch variations in music playback.

Innovation Solution

A signal processing system that includes a moving sleeve connected to a coil wrapped around a cone, with a ferromagnetic shaft inside, generating a voltage proportional to the audio signal and its distortion, allowing for the subtraction of distortion from the original signal to minimize or eliminate Doppler distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the speaker diaphragm moves outwardly to produce sound waves, then the sound output increases, but pitch distortion occurs due to the Doppler effect

Engineering Contradiction:

Improvesound outputVSAvoidpitch accuracy

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent generates a feedback signal by moving the coil through the magnetic field in response to diaphragm movement. This feedback signal contains the Doppler distortion components, which are then subtracted from the original audio signal to cancel out the distortion and recover the accurate pitch information.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces a magnetic field interaction mechanism as an intermediary. The coil moving through the magnetic field generates a voltage signal that mediates between the mechanical diaphragm movement and the electrical audio signal, allowing extraction and cancellation of Doppler distortion components.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple tones are present in the audio signal, then the music complexity increases, but Doppler distortion becomes more prevalent and complex

Engineering Contradiction:

Improvemusic complexityVSAvoidDoppler distortion

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The feedback mechanism captures the actual Doppler distortion produced by the speaker's motion, regardless of how complex the input signal is. By continuously generating feedback based on real-time diaphragm movement and subtracting it from the input, the system handles complex multi-tone music signals effectively.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent converts the harmful Doppler distortion into a useful feedback signal. The same physical phenomenon that causes distortion (coil movement through magnetic field) is harnessed to generate a cancellation signal, turning the harmful effect into a beneficial tool for distortion removal.

Inventive Principle:

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

3Manufacturing precision

If a coil is moved through a magnetic field to generate feedback voltage, then Doppler distortion can be cancelled, but device complexity increases

Engineering Contradiction:

Improvedistortion cancellationVSAvoiddevice complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent makes the voice coil serve multiple functions: it acts as both the actuator that drives the diaphragm and the sensor that generates the feedback signal for distortion cancellation. This multi-functionality eliminates the need for separate components, reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the feedback generation mechanism with the existing speaker components. The coil and magnetic field, already present in the speaker for driving the diaphragm, are combined with the feedback signal generation function, eliminating the need for separate feedback hardware.

Inventive Principle:

Principle #5Merging (Combining)

4Manufacturing precision

If crossover circuitry is added to reduce Doppler effect, then distortion decreases, but small speakers cannot be used

Engineering Contradiction:

Improvedistortion reductionVSAvoidcrossover circuitry

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces the electrical crossover circuitry with a mechanical/electromagnetic feedback mechanism. Instead of using complex electrical networks to manage different frequency ranges, the system uses the physical motion of the coil through the magnetic field to generate and subtract distortion signals, enabling use in small speakers without crossover circuits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system effectively reduces or eliminates Doppler distortion in loudspeakers, providing a more pleasing sound experience by compensating for the frequency shifts caused by the movement of the speaker cone within the magnetic field.

Implementation Method 1

movement of the speaker cone causes the coil to move through a magnetic field which creates a voltage across the coil

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS8189811B1System and method for processing audio signals

Publication Date: 2012.05.29 TILLIS ROY R

AI summary

An audio signal is processed by passing it through a speaker, the cone of which is mechanically connected to a moving sleeve. A coil is wrapped around the sleeve. There is a metal shaft displaced inside of the sleeve. The shaft is connected to a magnet. Thus, movement of the speaker cone causes the coil to move through a magnetic field which creates a voltage across the coil which is subtracted from the original audio signal to produce a processed output.