Adaptive Filter Bank for Directional Noise Suppression

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Solution Overview

Problem

Existing active noise cancellation (ANC) headphones are suboptimal in suppressing high- or low-frequency outside noise coming from various directions due to the use of a single fixed analog filter, which restricts noise cancellation effectiveness across different sound incidence directions.

Innovation Solution

The implementation of a headphone system with a filter bank comprising at least two adaptively linked analog filters, along with a voltage-controlled amplifier (VCA) and an error microphone, utilizes the least mean square (LMS) algorithm to generate an adaptive anti-interference signal, ensuring optimal noise cancellation across all sound incidence directions by dynamically adjusting the filter outputs based on the interference signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single fixed analog filter is used in ANC headphones, then the device complexity is reduced, but the noise cancellation effectiveness across different sound incidence directions deteriorates

Engineering Contradiction:

Improvefilter structureVSAvoidnoise cancellation effectiveness

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The single fixed analog filter is divided into multiple analog filters arranged in parallel, forming a filter bank. Each filter processes different aspects of the noise signal, allowing the system to handle various sound incidence directions effectively. This segmentation enables the system to achieve superior noise cancellation (up to 26 dB) compared to single-filter designs (14.5-6 dB), while maintaining manageable complexity through modular architecture.

Inventive Principle:

Principle #1Segmentation

2Object-affected harmful factors

If adaptively linked analog filters are used to improve noise cancellation for all directions, then the noise suppression performance is improved, but the device complexity increases

Engineering Contradiction:

Improvenoise suppression performanceVSAvoidfilter bank structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The analog filters are dynamically linked through adaptive weighting controlled by VCAs (voltage-controlled amplifiers). The weighting factors are adjusted in real-time based on feedback from the error microphone and the interference signal, allowing the filter bank to adapt to different sound incidence directions. This dynamic adaptation enables optimal noise suppression across all directions without requiring complex digital signal processing, achieving up to 26 dB suppression while managing device complexity through analog-based control.

Inventive Principle:

Principle #15Dynamics

3Object-affected harmful factors

If a filter bank with multiple analog filters is implemented, then the noise cancellation across all directions is improved, but the manufacturing complexity increases

Engineering Contradiction:

Improvenoise cancellation across directionsVSAvoidfilter bank assembly

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

Instead of using complex digital filters that require precise digital signal processing, the invention employs multiple analog filters with adjustable parameters. The analog filters use variable gain and frequency characteristics that can be tuned during manufacturing and operation. This approach simplifies manufacturing compared to high-precision digital filter implementation, while still achieving superior noise cancellation performance across all directions through the analog filter bank architecture.

Inventive Principle:

Principle #35Parameter changes

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 significantly enhances noise cancellation performance, achieving up to 26 dB of active noise suppression, as demonstrated by the reduction in residual noise spectrum, compared to the 14.5 dB and 6 dB achieved with fixed filters, thereby providing superior noise cancellation across all directions.

Implementation Method 1

a voltage-controlled amplifier (VCA) with weighting dependent on the interference signal is arranged between each adaptively linked analog filter and its filter output

Methodology Applied

Scientific EffectVoltage-controlled amplification:

Implementation Method 2

a loudspeaker arranged on the inside with a membrane

Methodology Applied

Scientific EffectElectroacoustic transduction:

Implementation Method 3

an error microphone is arranged after the membrane, which is fed back to a filtered x least mean square (fxLMS) circuit

Methodology Applied

Scientific EffectAcoustic to electrical conversion:

Data Source

PatentEP2677765B1Headphone for active noise suppression

Publication Date: 2018.11.28 AKG ACOUSTICS GMBH

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Figure 4~5

AI summary

Headphone for active noise suppression of surrounding influences, as occur at a construction site, in street or air traffic, in which two corresponding headphone cups (1) each include an externally arranged microphone (2) and an internally arranged loudspeaker (3) with membrane (6) and analog filter (H). For suppression of high- and low-frequency external noise coming from different directions, at least one parallel filter bank of at least two adaptively linked analog filters (H1, H2) is arranged in at least one headphone cup (i), whose filter outputs are connected to an adder (5), which is connected to the membrane (6) of at least one internal loudspeaker (3).