Active Damping of Ear Canal Resonances in ANR Devices
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Solution Overview
Problem
Existing acoustic devices with active noise reduction capabilities struggle to effectively dampen audio signals at high frequencies (3,000-10,000 Hz) due to resonant modes of the ear canal, leading to an unnatural listening experience and variability in performance across different users.
Innovation Solution
Implementing modal control to target and dampen audio signals at resonant frequencies of the ear canal by using existing hardware components, such as microphones and output transducers, without requiring additional sensors in the ear canal, and combining this with broadband noise reduction for lower frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If broadband control is used to cancel audio signals, then audio cancellation is achieved across a wide frequency range, but the upper frequency limit is restricted to 1,000-2,000 Hz
Solution Approach 1:
The patent divides the frequency range into two segments: low frequencies (below 1,000-2,000 Hz) handled by broadband control and high frequencies (3,000-10,000 Hz) handled by modal control targeting resonant modes. This segmentation allows each control method to operate optimally within its designated frequency band, resolving the contradiction between broadband cancellation effectiveness and high frequency coverage.
Solution Approach 2:
The patent merges broadband control and modal control into a unified active noise reduction system. The broadband control handles low frequency cancellation while modal control specifically targets high frequency resonant modes, creating a comprehensive solution that covers the entire audible spectrum effectively.
2Reliability
If in-ear headphones are inserted into the user's ears, then noise reduction is provided, but the resonant frequencies shift substantially causing an unnatural listening experience
Solution Approach 1:
The patent converts the harmful effect of resonant frequency shifts and peaks into a benefit by using modal control to actively dampen these resonances. The same ear canal geometry that causes problematic resonances when headphones are inserted becomes the target for selective damping, allowing the system to maintain noise reduction performance while restoring natural listening quality by reducing the unnatural resonant peaks.
3Measurement precision
If additional microphones are inserted into the user's ear canal to measure audio response, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses the existing output transducer as an intermediary to indirectly measure the audio response within the ear canal. Instead of inserting additional microphones, the system uses the transducer's known characteristics and the physics of resonant modes to infer the ear canal's resonant frequencies, thereby achieving measurement precision without increasing device complexity.
Solution Approach 2:
The system uses the existing hardware components (output transducer and existing microphones) to serve the dual purpose of audio output and resonant frequency measurement. The output transducer's interaction with the ear canal acoustics provides the measurement information needed for modal control, eliminating the need for additional dedicated measurement devices.
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
Improves the listening experience by reducing noise at high frequencies and minimizing head-to-head variability, providing a more natural audio response and personalized noise reduction.
Implementation Method 1
The ear canals of many humans have one or more strong acoustic resonant modes (e.g., between 2,000 Hz and 4,000 Hz). However, when using an acoustic device such as an in-ear headphones that are inserted into the user's ears, the frequencies of the resonant modes for a particular user can shift substantially
Implementation Method 2
actively damping the audio attributable to resonant modes of a user's ear canal
Data Source
AI summary
An active noise reduction (ANR) device includes an acoustic transducer, a first sensor, and a second sensor. The acoustic transducer is configured to generate output audio. The first sensor is configured to capture audio originating from an external environment of the ANR device. The second sensor is configured to generate a signal indicative of (1) the audio originating from the external environment and (2) the output audio generated by the acoustic transducer. The output audio generated by the acoustic transducer is modified based on a portion of the signal generated by the second sensor, the portion being attributable to a resonant mode of a user's ear canal.