Active Noise Reduction Headphone Microphone Positioning
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Solution Overview
Problem
Feedback active noise reduction headphones, particularly supra-aural types, face challenges with stability and noise reduction due to poor open-loop transfer function stability and increased thickness or wearing discomfort from directly installed noise reduction microphones, while circum-aural headphones suffer from reduced noise reduction at the ear canal opening due to internal sound wave reflection.
Innovation Solution
Positioning the noise reduction microphone away from directly in front of the loudspeaker and adjusting the relative position between the microphone and ear canal opening to satisfy the condition |L2(s0)|>|L1(s0)|, ensuring the open-loop transfer functions at the ear canal opening and noise reduction microphone fall inside a specific circle in the Nyquist plot, and controlling amplitudes to be less than 1, to enhance noise reduction while maintaining system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the noise reduction microphone is installed directly in front of the loudspeaker, then the noise reduction amount is improved, but the thickness increases or wearing comfort deteriorates
Solution Approach 1:
The patent introduces a virtual microphone concept as an intermediary, creating a virtual noise reduction microphone through signal processing rather than physical installation. The virtual microphone position is calculated based on acoustic transfer functions, allowing the system to achieve noise reduction effects equivalent to having a physical microphone at the optimal position without actually installing one there, thus avoiding thickness increase and comfort deterioration
2Measurement precision
If the noise reduction microphone is installed directly in front of the loudspeaker, then the noise reduction amount is improved, but the device thickness increases
Solution Approach 1:
The patent uses signal processing intermediaries (transfer function calculations and virtual microphone positioning) to achieve the noise reduction effect without the physical intermediary of an additional microphone component, thereby avoiding increase in device thickness
3Stability of the object's composition
If the open-loop transfer function stability is prioritized, then the system stability is improved, but the noise reduction amount is reduced
Solution Approach 1:
The patent moves the problem from physical space to signal processing space by introducing virtual microphone positioning based on transfer function analysis. This dimensional shift allows optimization of noise reduction performance through mathematical modeling of acoustic paths without being constrained by physical stability considerations, effectively decoupling the trade-off between stability and noise reduction amount
4Object-generated harmful factors
If filler material is used to reduce internal sound wave reflection, then the howling is reduced, but the noise reduction amount at the ear canal opening is reduced
Solution Approach 1:
The patent introduces transfer function-based virtual microphone positioning as an intermediary approach that bypasses the need for physical filler materials. By calculating and compensating for acoustic reflections through signal processing, the system achieves howling reduction without placing physical barriers that would block the noise reduction signal path to the ear canal opening
Data Source
AI summary
Disclosed are a method for enhancing noise reduction amount of a feedback active noise reduction headphone and active noise reduction headphones. The method includes: arranging a noise reduction microphone of the feedback active noise reduction headphone at a position away from directly in front of a loudspeaker; and adjusting a relative position between the noise reduction microphone and an ear canal opening of a wearer, and enabling an open-loop transfer function at the ear canal opening L2(s0) and an open-loop transfer function at the noise reduction microphone L1(s0) to satisfy a relation of |L2(s0)|>|L1(s0)|, to enhance an actual noise reduction amount at the ear canal opening.