Speaker Excursion Limiter With Low-Delay Parallel Filter Paths
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Solution Overview
Problem
Existing excursion limiters for audio speakers often introduce excessive group delay, particularly at low frequencies, leading to unwanted audible artifacts such as smearing of time response, and may not effectively minimize excursion-related damage to the driver.
Innovation Solution
A system and method utilizing a combination of lowpass, highpass, and allpass filter circuitries, along with clipping circuitry, to generate an excursion limiting output signal that minimizes group delay at low input levels while controlling excursion at high output levels, using configurations such as 3rd or 5th order Butterworth filters and allpass filters to ensure phase alignment and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-Q filters are used in excursion limiter, then excursion control effectiveness is improved, but group delay increases causing audible time-domain transient response problems
Solution Approach 1:
The excursion limiter is divided into multiple parallel filter paths (first and second lowpass filter paths, first and second highpass filter paths) with different Q factors. Each path processes the input signal independently and their outputs are combined, allowing the system to achieve effective excursion control while minimizing overall group delay through the parallel architecture.
Solution Approach 2:
Instead of using a single high-Q filter that would provide complete excursion control but excessive group delay, the patent applies multiple filters with progressively lower Q factors in parallel. This partial action approach ensures that each filter contributes to excursion control without any single filter introducing excessive time delay, achieving a balance between control effectiveness and temporal fidelity.
2Reliability
If standard high pass filter is used to protect woofer from excessive excursion, then driver protection is improved, but low frequency bandwidth is limited and spectral quality is compromised
Solution Approach 1:
The protection function is segmented across multiple parallel filter paths with different characteristics. The first lowpass path and first highpass path handle certain frequency ranges, while the second lowpass path and second highpass path handle other ranges. This segmentation allows each path to use gentler filter slopes, collectively providing comprehensive driver protection while preserving extended low frequency bandwidth.
Solution Approach 2:
The parallel filter architecture serves multiple functions simultaneously: it protects the driver from excessive excursion, preserves low frequency bandwidth, maintains spectral quality, and minimizes group delay. Each filter path contributes to multiple objectives, making the system universally effective across different operating conditions and frequency ranges.
3Ease of operation
If excursion limiter is tuned to take effect only at high listening levels, then sound quality at low levels is preserved, but excursion-related damage protection may be insufficient
Solution Approach 1:
The excursion limiter dynamically adapts its control characteristics across different input levels through the parallel filter architecture. At low listening levels, the system preserves signal fidelity with minimal intervention. As input levels increase and approach dangerous excursion thresholds, the parallel filter paths progressively engage to provide stronger excursion control, creating a dynamic response that adapts to operating conditions.
Solution Approach 2:
The multiple parallel filter paths are pre-configured with different Q factors and cutoff frequencies to anticipate different operating scenarios. This preliminary configuration ensures that appropriate filter paths are already in place to handle various input levels, allowing the system to provide both sound quality preservation at low levels and comprehensive protection at high levels without real-time adjustment delays.
Data Source
AI summary
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.