Active Noise Control Filter for Acoustic Mode Stability
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Solution Overview
Problem
Existing active noise reduction devices face instability in noise cancellation due to acoustic modes in vehicle compartments, leading to inconsistent noise reduction at different control points.
Innovation Solution
An active vibration noise reduction device utilizing a control filter that adaptively updates using the sum of squares of sound pressures from multiple microphones as an evaluation function, along with secondary path filters and adaptive algorithms to stabilize noise reduction across multiple control points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signals from multiple microphones are added up as error signals in a vehicle compartment, then noise reduction can be achieved at control points, but acoustic modes cause certain frequency signals to be enhanced or canceled, leading to instability in noise reduction
Solution Approach 1:
The patent changes the evaluation function parameter from simple sum of error signals to sum of squares of sound pressures. This parameter transformation resolves the instability caused by acoustic modes, as the squared pressure values remain positive and contribute constructively to the evaluation function regardless of phase relationships, enabling stable noise reduction across wide frequency ranges
Solution Approach 2:
The patent substitutes the conventional error signal summation approach with a sound pressure squared summation approach. This substitution transforms the mathematical operation from linear addition (which is sensitive to phase cancellation) to quadratic addition (which is not), thereby replacing the problematic mechanical signal processing method with a more robust alternative
2Adaptability or versatility
If a control filter is updated using conventional error signals, then adaptation to noise patterns can occur, but acoustic modes prevent effective control when error signals are canceled
Solution Approach 1:
The patent transforms the update parameter from conventional error signals to sum of squares of sound pressures. This parameter change ensures that the adaptive filter receives always-positive contributions from all microphone channels, preventing cancellation effects and enabling reliable adaptation across all frequency ranges including those affected by acoustic modes
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
Stable noise reduction is achieved across a wide range by adaptively updating control filters and secondary path filters, ensuring consistent noise cancellation regardless of acoustic modes or seat adjustments.
Implementation Method 1
generate a cancellation sound having a phase opposite to that of noise (for example, road noise) generated in a vehicle compartment and causing the generated cancellation sound to interfere with the noise
Implementation Method 2
a plurality of microphones for generating a plurality of error signals, each of the plurality of microphones generating a respective one of the plurality of error signals from the noise and the cancellation sound
Data Source
AI summary
An active vibration noise reduction device includes: a speaker for outputting a cancellation sound for canceling a noise, a plurality of microphones each for generating an error signal from the noise and the cancellation sound, and a control filter configured to generate a control signal for controlling the cancellation sound based on the error signals generated by the plurality of microphones. The control filter is adaptively updated using a sum of squares of sound pressures of the error signals generated by the plurality of microphones as an evaluation function.