Sealed Speaker Equalization With Variable Sub-Resonance Cutoff
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Solution Overview
Problem
Existing audio signal processing technologies fail to generate speaker feeds that provide a flat frequency response below a speaker's resonance frequency without exceeding the speaker's excursion limit, leading to potential physical damage and distortion.
Innovation Solution
A digital signal processing (DSP) based equalizer is used to generate a speaker feed with a variable sub-resonance frequency range, adjusting parameters to boost gain at sub-resonance frequencies and prevent over-excursion, ensuring a flat frequency response from resonance frequency down to a feedback-determined sub-resonance frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gain is boosted at sub-resonance frequencies to achieve flat frequency response, then frequency response quality is improved, but speaker excursion limit is exceeded causing potential damage
Solution Approach 1:
The patent applies dynamics by making the high-pass filter cutoff frequency variable rather than fixed. The cutoff frequency automatically adjusts based on the speaker's operating conditions, particularly the excursion limit. When the speaker operates at high power levels where excursion limits are approached, the filter dynamically raises the cutoff frequency to prevent over-excursion. At lower power levels, the cutoff frequency lowers to allow broader sub-resonance frequency reproduction. This dynamic adaptation resolves the contradiction between maintaining flat frequency response and protecting the speaker from damage.
Solution Approach 2:
The patent implements feedback by monitoring the speaker's excursion status and using this information to control the high-pass filter characteristics. The system continuously adjusts the filter cutoff frequency in response to feedback about the speaker's mechanical state, ensuring that gain boosting at sub-resonance frequencies does not cause the speaker to exceed its excursion limit. This closed-loop control resolves the contradiction by adapting the frequency response to the speaker's safe operating range.
2Reliability
If a fixed high-pass filter is used to prevent over-excursion, then speaker protection is improved, but frequency response range is reduced due to unnecessary gain reduction
Solution Approach 1:
The patent replaces the fixed high-pass filter with a dynamic filter whose cutoff frequency automatically adjusts based on operating conditions. Instead of permanently blocking sub-resonance frequencies below a fixed threshold, the filter only raises the cutoff when necessary to prevent over-excursion at high power levels. At lower power levels, the filter allows the full sub-resonance frequency range to pass through, providing flat frequency response. This dynamic behavior resolves the contradiction between speaker protection and frequency range by applying protection only when needed.
Data Source
AI summary
Methods and systems for generating a speaker feed for driving a sealed speaker, including: generating feedback indicative of excursion of the speaker; in response to the feedback, equalizing an input signal to generate the speaker feed, such that the speaker feed is equalized for driving the speaker with: a desired frequency response above the speaker's resonance frequency; and an at least substantially flat frequency response in a variable sub-resonance equalization band without exceeding the speaker's excursion limit, where the sub-resonance equalization band extends from the resonance frequency down to a variable cutoff frequency, and the cutoff frequency is determined in response to the feedback. The speaker feed is generated in a feedback-controlled filter configured to boost the input signal at frequencies in the sub-resonance equalization band, the boost having a sloping frequency-amplitude response whose slope is set to overcome or cancel the speaker's natural falloff in the speaker's spring-loaded region.