Audio Speaker Excursion Limiting With Perfect-Reconstruction Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Audio speakers face issues with excessive group delay, leading to unwanted audible artifacts, especially at low frequencies, due to the use of excursion limiters with high-Q filters, which can result in smearing of time response and transient response problems.
Innovation Solution
A system and method for minimizing excursion in audio speakers using a configuration with lowpass and highpass filtering circuitries, allpass filtering, and clipping circuitry, which operates as a perfectly reconstructing system at low input levels and limits excursion at high output levels by generating a clipped fundamental plus odd-order harmonics, filtered out by subsequent bandpass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-Q filters are used in excursion limiters, then excursion limiting effectiveness is improved, but group delay increases causing audible time-domain transient response problems
Solution Approach 1:
The signal processing is divided into multiple frequency bands using parallel bandpass filters with different Q factors. Each band handles specific frequency ranges, allowing the system to achieve effective excursion limiting across the entire audio spectrum while maintaining low group delay in critical low-frequency regions where high-Q filters would otherwise cause problematic delays.
Solution Approach 2:
Different filter Q factors are applied to different frequency bands according to their specific requirements. Low-frequency bands use lower Q filters to minimize group delay and transient response issues, while higher-frequency bands can tolerate higher Q factors for effective excursion limiting, thus optimizing performance locally in each frequency region.
2Duration of action of stationary object
If excursion limiters are used to protect woofers, then driver life is extended, but low-frequency bandwidth may be affected
Solution Approach 1:
The system dynamically adjusts the limiting threshold and filter characteristics based on the input signal level and frequency content. At low input levels, the excursion limiter remains transparent to preserve low-frequency bandwidth and natural sound. At high input levels, the limiter activates to protect the driver, thus providing adaptive protection that maintains performance across different operating conditions.
Solution Approach 2:
The excursion limiter applies partial limiting only when and where needed (at high signal levels and specific frequency bands), rather than continuously across the entire frequency spectrum. This selective application preserves low-frequency bandwidth during normal operation while providing sufficient protection during high-level signals that would otherwise cause damaging excursion.
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present disclosure generally relates to a system for limiting the excursion of an audio speaker. The system may include first lowpass filter circuitry configured to receive a system input signal and to generate a first signal. The system may further include clipping circuitry configured between the first lowpass filter circuitry and the first combiner circuitry. The system may include first highpass filter circuitry configured to receive the system input signal and to generate a second signal. The system may include second lowpass filter circuitry configured to receive a combined output signal from the first combiner circuitry. The system may include allpass filter circuitry configured to receive the system input signal and to generate a fourth signal. The system may include second highpass filter circuitry configured to receive the fourth signal from the allpass filter circuitry. The second combiner circuitry may be configured to generate an excursion limiting output signal.