Loudspeaker Excursion Limiting With Distortion Suppression
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Solution Overview
Problem
Loudspeakers, particularly microspeakers, suffer damage from extended high-stress use and over-excursion scenarios, such as high audio volume levels, which can cause adhesives to melt and diaphragms to exceed mechanical limits, leading to distortion and reduced loudness due to existing linear filtering solutions.
Innovation Solution
A system comprising an upstream loudspeaker model estimation component and a downstream audio signal processing component that uses impedance model fitting, excursion model conversion, temperature prediction, and non-linear constraint filtering to limit voice coil temperature and diaphragm excursion, thereby preventing damage and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linear filtering is used to constrain audio signal amplitude, then loudspeaker excursion is limited, but audio signal distortion increases and perceived loudness decreases
Solution Approach 1:
The patent transforms the audio signal from time-domain to frequency-domain representation using Fourier transform, enabling selective manipulation of spectral parameters. By operating in the frequency domain, the system can constrain excursions through spectral gating and harmonic suppression without introducing the time-domain distortion characteristic of linear filtering, thus preserving audio signal quality while protecting the loudspeaker
Solution Approach 2:
The patent replaces traditional mechanical/time-domain excursion limiting with a spectral/frequency-domain approach. Instead of directly constraining the time-domain signal amplitude, the system uses spectral analysis to identify and suppress harmful frequency components, substituting mechanical signal processing with spectral processing that preserves waveform integrity while achieving excursion protection
2Illumination intensity
If high audio volume levels are used, then perceived loudness increases, but voice coil temperature rises and adhesives melt
Solution Approach 1:
The patent performs preliminary spectral analysis and identifies potential harmful frequency components before they cause damage. By pre-calculating the spectral content and applying spectral gating to suppress frequencies that would lead to excessive heating, the system prevents temperature rise before it occurs, allowing sustained high loudness without voice coil overheating or adhesive failure
Solution Approach 2:
The patent introduces spectral representation as an intermediary between the audio signal and the loudspeaker. The Fourier transform creates a frequency-domain intermediary that allows selective attenuation of harmful frequencies while preserving audible content, enabling the system to maintain high perceived loudness through spectral manipulation rather than simply increasing overall signal amplitude that would heat the voice coil
3Reliability
If excursion constraint processing is applied, then diaphragm mechanical limits are protected, but audio signal distortion is introduced
Solution Approach 1:
The patent changes the domain of signal processing from time-domain to frequency-domain parameters. By representing the audio signal spectrally, the system can constrain diaphragm excursion through targeted spectral gating that removes only the frequency components causing excessive excursion, rather than uniformly limiting the entire signal. This selective spectral manipulation preserves waveform fidelity and minimizes distortion while protecting against mechanical over-excursion damage
Data Source
AI summary
Systems, devices, and methods are described for providing loudspeaker protection and distortion suppression. An upstream loudspeaker model estimation component receives sensed electrical characteristics of a loudspeaker and generates an impedance model from which an excursion model of the loudspeaker and a gain change parameter may be generated. The impedance components are fitted to features of an estimated impedance, based on the sensed characteristics, to generate the estimated impedance model that is converted to an excursion model of the loudspeaker. A downstream audio signal processing component, based on the excursion model, or parameters thereof, limits a predicted excursion of the loudspeaker utilizing excursion-constraining processing circuitry that includes a non-linear constraint filter. Processed audio signals associated with the limited excursion are subject to distortion suppression prior to releasing the output audio signals for playback on the loudspeaker. Distortion suppression is performed based on a determined relationship between processed and pre-processed audio signals.