Headphone ANC Dynamic Range Control for Speaker Protection
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Solution Overview
Problem
Sealed in-ear headphones can cause the occlusion effect, leading to speaker overdriving due to trapped air and loud ambient noise, potentially damaging the speaker and affecting user experience.
Innovation Solution
A digital audio signal processing method that filters microphone signals using adaptive filters in feedforward and feedback paths, applying dynamic range control with low shelf cut filters to prevent speaker overdriving, particularly in loud environments and during physical activities like walking, and attenuates infrasound to improve user experience during events like riding a bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If acoustic noise cancellation system actively reproduces user's voice through the speaker to mitigate occlusion effect, then user experience is improved, but speaker may be overdriven and damaged
Solution Approach 1:
The system uses a feedback path with a first microphone inside the headphone to detect sound pressure levels within the wearer's ear, and uses this feedback information to dynamically adjust the audio signal sent to the speaker, preventing overdriving while maintaining noise cancellation effectiveness
Solution Approach 2:
The system dynamically adjusts the audio signal in real-time based on detected sound pressure levels and ambient noise conditions, varying the signal strength and frequency content to prevent speaker overdriving while maintaining effective noise cancellation and occlusion effect mitigation
2Object-affected harmful factors
If ANC system processes audio signals to cancel ambient noise, then noise cancellation performance is improved, but speaker excursion limit is exceeded under loud ambient conditions
Solution Approach 1:
The system changes audio signal parameters including frequency content and amplitude based on ambient noise levels and speaker displacement estimates, using adaptive filtering and dynamic range control to maintain noise cancellation while preventing speaker excursion limits from being exceeded
Solution Approach 2:
The system applies partial attenuation to specific frequency ranges (particularly low frequencies below 20Hz) using dynamic range control and low shelf cut filters, reducing only the excessive portions of the signal that would cause speaker overdriving while preserving the essential noise cancellation functionality
3Object-affected harmful factors
If sealed in-ear headphone design is used to acoustically isolate ambient noise, then passive noise isolation is improved, but occlusion effect is intensified
Solution Approach 1:
The system converts the harmful occlusion effect into a beneficial feature by actively reproducing the user's own voice through the speaker, using the trapped air pocket and occlusion effect as an acoustic amplifier to deliver the user's voice back to them with enhanced clarity and presence
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively protects the speaker from overdriving and enhances user experience by reducing noise and artifacts, maintaining sound quality in loud environments and during motion.
Implementation Method 1
The feedforward and feedback paths may be part of an ANC system and can be configured to process the respective audio signals to result in anti-noise produced by the speaker, intended to acoustically cancel any external or ambient noise
Implementation Method 2
The dynamic range control includes producing the first DRC adjusted signal by a first low shelf cut filter, and then applying a second low shelf cut filter to the first DRC adjusted signal
Data Source
AI summary
A method for audio signal processing of microphone signals of a headphone. An audio signal from a first microphone of a headphone is filtered by an ANC system to produce a first filtered signal. Dynamic range control is performed upon the first filtered signal to produce a first dynamic range adjusted signal that drives a speaker of the headphone. Other aspects are also described and claimed.