Feedforward ANR Acoustics: Leak Aperture and Windscreen Design
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Solution Overview
Problem
Existing personal active noise reduction (ANR) devices face challenges in effectiveness due to wind noise and occlusions, which can lead to increased noise generation and poor noise attenuation, especially in feedforward-based systems where microphones detect localized vortices and occlusions block environmental noise access.
Innovation Solution
The design incorporates a combination of feedforward and feedback-based ANR, along with passive noise reduction, using a controlled leak aperture and acoustically resistive and mass ports to stabilize noise reduction across audible frequencies, and a vibration isolator to minimize interference from external vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedforward microphone is acoustically coupled to the surrounding environment to detect noise sounds, then feedforward-based ANR can be implemented, but wind noise and localized vortices generate additional noise that cannot be correlated with earpiece acoustic noises
Solution Approach 1:
A windscreen is introduced as an intermediary component between the feedforward microphone and the external environment. The windscreen allows acoustic waves to pass through to the microphone while physically blocking direct wind flow and vortex formation at the microphone diaphragm, thereby eliminating wind noise without compromising feedforward ANR functionality
Solution Approach 2:
The harmful wind noise and vortex noise are extracted and separated from the useful environmental noise signal. By protecting the microphone from direct wind exposure while maintaining acoustic coupling, the system isolates the microphone from harmful factors while preserving its ability to detect relevant noise for ANR processing
2Ease of manufacture
If occlusions physically block the access of the feedforward microphone to the surrounding environment, then the device structure is simplified, but environmental noise sounds are greatly attenuated resulting in poorer noise attenuation
Solution Approach 1:
The earpiece housing incorporates porous or perforated materials that allow acoustic waves to pass through while maintaining structural integrity and simplicity. These porous structures provide acoustic access to the feedforward microphone without requiring complex open designs, thereby preserving noise attenuation performance while keeping the device structure relatively simple
3Object-affected harmful factors
If passive noise reduction is used to isolate ears from environmental noise, then physical isolation is achieved, but variability in seal quality causes variability in noise reduction effectiveness
Solution Approach 1:
A feedback microphone is implemented to continuously monitor the actual acoustic environment inside the earpiece. The feedback signal is used to adjust the active noise reduction output in real-time, compensating for variations in passive seal quality and ensuring consistent noise reduction performance across different wearing conditions
Solution Approach 2:
The system merges passive noise reduction (physical isolation) with active noise reduction (electronic counter-noise generation). This combination allows the system to benefit from both the physical blocking of high-frequency noise and the electronic cancellation of low-frequency noise, providing more consistent overall performance than passive isolation alone
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
This approach enhances the consistency and effectiveness of noise reduction across a wide range of frequencies, reducing variability in passive noise reduction and improving the performance of feedforward-based ANR by maintaining acoustic access to environmental noise while minimizing interference from occlusions and wind noise.
Implementation Method 1
an acoustic driver disposed within the casing to acoustically output anti-noise sounds into the front cavity
Implementation Method 2
a feedback microphone disposed within the front cavity to detect noise sounds present within at least the front cavity
Implementation Method 3
a feedforward microphone carried by the casing and acoustically coupled to the environment external to the casing
Implementation Method 4
a leak aperture formed in the casing to couple the front cavity to the environment external to the casing to reduce variability in the passive noise reduction
Implementation Method 5
the ear coupling being structured to engage the portion of the head of the user to form at least a partial seal between the ear coupling and the portion of the head of the user to provide passive noise reduction
Data Source
AI summary
An earpiece of an ANR device incorporates one or more of feedforward-based ANR; feedback-based ANR; passive noise reduction (PNR) of environmental noise sounds in the environment external to the casing of the earpiece in higher audible frequencies; a controlled leak acoustically coupling the front cavity to the environment external to the casing of the ANR device where the coupling may be through another cavity that is closable to the environment external to the casing with a leaky cover; a combination of an acoustically resistive port and a mass port coupling a rear cavity to the environment external to the casing where the coupling may be through another cavity that is closable to the environment external to the casing with a leaky cover; a feedforward microphone given acoustic access to the environment external to the casing through an aperture that is overlain with a leaky cover or that is enclosed within a cavity that is acoustically coupled to the environment external to the casing with a leak.