Loudspeaker Excursion Modeling via Linear-Nonlinear Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The characterization of loudspeakers is challenging due to their non-linear response, which introduces frequency content not present in the input signal, making it difficult to model and compensate for, especially in small, cost-effective microspeakers used in applications like mobile devices.
Innovation Solution
A method involving filtering an input test signal with the inverse of a linear model to measure the loudspeaker's excursion, determining non-linear parameters for a more accurate non-linear model, and using this model to modify audio signals for improved sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital signal processing and active control are used to compensate for poor sound quality, then sound quality is improved, but device complexity increases due to the need for accurate loudspeaker modeling
Solution Approach 1:
The loudspeaker model is segmented into separate linear and non-linear components. The linear model captures the primary loudspeaker behavior, while the non-linear model specifically addresses distortion products. This segmentation allows the complex non-linear behavior to be handled separately, reducing the overall modeling complexity while maintaining accuracy for sound quality compensation.
Solution Approach 2:
An inverse filter is introduced as an intermediary component that uses the determined non-linear parameters to pre-distort the input signal. This inverse filter acts as a mediator between the audio source and the loudspeaker, compensating for non-linearities before the signal reaches the loudspeaker, thereby simplifying the overall system complexity while improving sound quality.
2Reliability
If non-linearities are modeled accurately to compensate for distortion, then sound quality is improved, but measurement and characterization difficulty increases
Solution Approach 1:
The method performs preliminary measurement of the loudspeaker's non-linear behavior by capturing distortion products generated in response to a test signal. These measurements are taken before the actual sound reproduction, allowing the non-linear parameters to be determined in advance. This preliminary characterization simplifies subsequent sound quality compensation by having the non-linear model parameters readily available.
Solution Approach 2:
The method converts the harmful effect of non-linear distortion into a useful measurement tool. By intentionally generating distortion products through a test signal and measuring them, the method transforms the difficult-to-measure non-linear behavior into a quantifiable set of parameters. These distortion products, which would normally degrade sound quality, become the basis for determining the non-linear model parameters needed for compensation.
Data Source
AI summary
A method for characterizing a loudspeaker comprises: filtering an input test signal by applying the inverse of a linear model describing an excursion of the loudspeaker in response to a given input signal, the linear model containing only linear terms; applying the filtered input test signal to the loudspeaker; measuring the excursion of the loudspeaker in response to the filtered input test signal; and, based on the measured excursion, determining one or more non-linear parameters for a non-linear model describing the excursion of the loudspeaker in response to a given input signal.