Voice Coil Current Control for Loudspeaker Nonlinearity Compensation
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Solution Overview
Problem
Existing loudspeaker technologies face challenges in achieving accurate linearization due to inherent nonlinearities, particularly in automotive and portable devices, where size and cost constraints hinder the use of high-end components, and existing control methods using membrane acceleration, velocity, or displacement are inaccurate and noisy, limiting frequency response and introducing distortions.
Innovation Solution
A controller that uses a neural network to directly control the current in the voice coil, combining current linearization with static force factor inversion, eliminating the need for real-time measurements and physical sensors, and compensating for nonlinearities by transforming input audio signals into desired current and voltage signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If expensive materials and high-end construction components are used to achieve linear performance, then loudspeaker linearity is improved, but cost and size increase
Solution Approach 1:
The patent applies digital signal processing to transform the input audio signal by applying the inverse of the loudspeaker's nonlinear response function, thereby changing the signal parameters to compensate for nonlinearities without physically modifying the loudspeaker components
Solution Approach 2:
The patent replaces physical/mechanical solutions (expensive materials and high-end construction components) with a digital signal processing approach, substituting the mechanical system with an electronic control system that achieves linearization through software algorithms
2Measurement precision
If accelerometer sensors are attached to the loudspeaker membrane to measure acceleration, then measurement capability is improved, but moving mass increases and performance deteriorates
Solution Approach 1:
The patent extracts the measurement function from physical sensors attached to the membrane and implements it through digital signal processing of the input audio signal, eliminating the need for physical accelerometers on the moving membrane
Solution Approach 2:
The patent uses the input audio signal as an intermediary to derive membrane acceleration information without physically measuring it, computing acceleration from the known input signal and the loudspeaker's response characteristics rather than direct sensing
3Measurement precision
If contactless laser methods are used to measure membrane velocity or displacement, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the measurement information from the input audio signal itself and uses digital signal processing to compute velocity and displacement, eliminating the need for external laser measurement systems
Solution Approach 2:
The system uses the input audio signal to provide its own measurement data, processing the signal through the known response function to derive membrane velocity and displacement without requiring external measurement devices
4Speed
If displacement-based control is used, then low-frequency response is improved, but high-frequency control accuracy deteriorates due to low-pass character
Solution Approach 1:
The patent dynamically adapts the control approach by using different derived quantities from the input signal for different frequency ranges, switching between displacement, velocity, and acceleration information based on the frequency content to maintain accuracy across the full frequency spectrum
Solution Approach 2:
The patent changes the control parameter from displacement to velocity or acceleration depending on the frequency range, using parameter transformation to overcome the low-pass limitation of displacement-based control at high frequencies
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 approach enables precise linearization of loudspeakers, enhancing sound quality and frequency response, extending the dynamic range, and optimizing performance without compromising size or cost, while maintaining consistent audio reproduction across frequencies.
Implementation Method 1
The response of a loudspeaker refers to the relationship between the input audio signal and the resulting acoustic audio output from the loudspeaker... the relation between a voice coil current signal i(t) of the loudspeaker and the voltage input signal u(t)
Data Source
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AI summary
The present invention relates to a controller for controlling a loudspeaker. The controller is configured to generate a loudspeaker control voltage signal from an input audio signal. The controller comprising circuitry configured to execute: a current model function configured to transform the input audio signal into a representation of a current signal; a voice coil displacement model function configured to determine a voice coil displacement signal from the input audio signal; a force factor compensation function configured to determine a force factor compensation signal based on the voice coil displacement signal and a force factor curve of the loudspeaker; a combining function configured to combine the representation of the current signal and the force factor compensation signal into a target current signal; and a nonlinear mapping function configured to transform the target current signal into the loudspeaker control voltage signal