Backpropagation Distortion Compensation in Loudspeaker Waveguides

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Solution Overview

Problem

Conventional loudspeaker systems with waveguides suffer from air path distortions at high sound pressure levels, leading to intermodulation and harmonic distortions that degrade sound quality, hindering the ability to produce high fidelity sound.

Innovation Solution

A method involving a pre-correcting engine that uses a backpropagation partial differential equation model to compensate for air path distortions by virtually propagating a target signal in reverse through a waveguide, generating a pre-corrected signal that mitigates wave steepening distortions, thereby improving sound fidelity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If sound waves propagate through the waveguide at high sound pressure levels, then the loudspeaker system can produce high volume sound, but the speed of sound varies causing intermodulation and harmonic distortions that degrade sound quality

Engineering Contradiction:

Improvesound volumeVSAvoidsound fidelity

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by pre-distorting the audio signal before it enters the waveguide. The system calculates the expected nonlinear distortions that will occur during wave propagation and applies the inverse distortion to the input signal, so that the distortions introduced by the waveguide cancel out the pre-applied opposite distortions, resulting in faithful sound reproduction at high volumes

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by measuring the actual sound output from the waveguide and using this information to adjust and refine the pre-distortion calculation. The system continuously monitors the output signal quality and modifies the pre-correction parameters to optimize compensation for air path distortions, ensuring accurate sound fidelity across varying operating conditions

Inventive Principle:

Principle #23Feedback

2Power

If the speed of sound varies within the waveguide due to sound pressure level changes, then high volume sound can be produced, but wave steepening distortions occur that degrade the quality of emitted sound

Engineering Contradiction:

Improvesound pressure levelVSAvoidwave steepening distortions

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by introducing a pre-correction signal that is specifically designed to counteract the wave steepening distortions that will occur during propagation. The system calculates the anticipated distortion pattern caused by varying sound speeds and generates an opposing distortion pattern in the input signal, so that when the wave propagates through the waveguide, the harmful steepening effects are canceled by the pre-applied opposite distortions

Inventive Principle:

Principle #9Preliminary anti-action

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 air path distortions, enabling loudspeaker systems to produce high fidelity sound at high volumes by compensating for variations in sound speed within the waveguide, resulting in a high fidelity output sound wave.

Implementation Method 1

configuring a backpropagation distortion compensation model based on one or more parameters associated with a waveguide included in the audio system, wherein the backpropagation distortion compensation model corrects for a mechanism that generates air path distortions attributable to wave propagation in waveguides

Methodology Applied

Scientific EffectBackpropagation:

Implementation Method 2

variations in the speed of sound in the air path lead to intermodulation and harmonic distortions in the sound wave

Methodology Applied

Scientific EffectWave propagation:

Implementation Method 3

at high sound pressure levels, the speed of sound in the waveguide changes and distorts the sound waves propagating through the waveguide

Methodology Applied

Scientific EffectSpeed of sound variations: Speed of Sound

Data Source

PatentUS9820046B2Compensation of air path distortions using backpropagation

Publication Date: 2017.11.14 HARMAN INT IND INC

AI summary

In one embodiment, a pre-correcting engine generates a pre-corrected signal that may be used to mitigate air path distortions in sounds generated by loudspeaker systems that include loudspeakers coupled to waveguides. In operation, the pre-correcting engine virtually propagates a target signal in a reverse direction from the output of the waveguide to the output of a driver. Notably, the pre-correcting engine implements a propagation distortion compensation model that, when applied to the target signal, corrects for the effects of air path distortions on the target signal. The pre-correcting engine then transmits the pre-corrected signal to the driver. As the driver drives the waveguide based on the pre-corrected signal, effects of the pre-corrected distortions negate effects of air path distortions and the loudspeaker system generates high-fidelity sounds. By contrast, conventional loudspeaker systems that drive the waveguide based on the target signal typically generate lower fidelity sounds that include air path distortions.