Active Noise Control with Dynamic Control Point Switching
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Solution Overview
Problem
Conventional noise reduction methods, such as active attenuating means using loudspeakers, are ineffective at high noise levels as they exceed the loudspeaker's reproducing capability, leading to deteriorated noise reduction effects in enclosed spaces like airplanes.
Innovation Solution
A noise reduction apparatus with multiple loudspeakers, control sound signal generating units, and error microphones that dynamically adjust the number of control points and error audio signal input based on noise levels, allowing the loudspeakers to operate within their dynamic range by generating control sounds to cancel noise at specific points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single loudspeaker is used to generate control sounds for noise cancellation, then the device complexity is low, but the noise reduction capability deteriorates at high noise levels exceeding the loudspeaker's reproducing capability
Solution Approach 1:
The patent divides the noise cancellation task across multiple loudspeakers positioned at different locations. Each loudspeaker handles a specific spatial zone, allowing the system to cover a broader frequency and spatial range without requiring any single loudspeaker to exceed its reproducing capability. This segmentation enables effective noise reduction even when overall noise levels are high.
2Reliability
If multiple control points are used to reduce noise at multiple locations, then the noise reduction coverage is improved, but the device complexity and signal processing load increase
Solution Approach 1:
The system dynamically adjusts the number and positioning of control points based on the detected noise characteristics and loudspeaker capabilities. When noise levels are high, the system optimizes by using fewer control points to prevent any single loudspeaker from being overloaded, while still maintaining effective noise reduction coverage. This dynamic adaptation resolves the contradiction between coverage and complexity.
3Reliability
If the loudspeaker operates at maximum output to cancel high noise levels, then the noise reduction effect is improved, but the reproducing capability is exceeded leading to distortion and deterioration
Solution Approach 1:
Instead of requiring a single loudspeaker to produce excessive output that exceeds its reproducing capability, the system distributes the required sound pressure level across multiple loudspeakers. Each loudspeaker operates within its optimal power range, producing partial control sounds that collectively achieve the necessary noise cancellation effect without distortion.
4Reliability
If error audio signals from multiple control points are fed to all control sound signal generating units, then the noise reduction at all points is optimized, but the signal processing complexity increases
Solution Approach 1:
The system implements local quality by feeding error audio signals selectively - each control sound signal generating unit receives error signals primarily from its corresponding control point. This localized signal processing approach maintains optimal noise reduction at each position while avoiding the excessive complexity of distributing all error signals to all generating units. The system processes signals locally where they are most needed.
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 reduces noise levels regardless of the noise intensity by optimizing the loudspeaker's output within its capabilities, ensuring consistent noise cancellation even at high noise levels.
Implementation Method 1
an audio regulating unit that amplifies the electric signal received from the microphone and inverts a phase of the electric signal
Implementation Method 2
Since the phase of the sound from the loudspeaker and the phase of the sound from the sound source are different from each other by 180 degrees, a silent part can be formed in a sound field
Implementation Method 3
error microphones, each of the error microphones is arranged at a corresponding control point of the plurality of control points and detecting error sound between the noise at the corresponding control point and the control sound at the corresponding control point
Data Source
AI summary
The noise reduction apparatus according to the present disclosure includes a plurality of loudspeakers, control sound signal generating units, and a plurality of error microphones. Each of the control sound signal generating units generates control sound signal based on the error sound detected by a corresponding error microphone of the plurality of error microphones. The noise reduction apparatus further including an input switching unit that, when a level of the noise at a predetermined position is higher than the predetermined threshold value, feeds an error audio signal at a predetermined control point of the plurality of control points or a control point that is newly set based on the plurality of control points into each of the control sound signal generating units, the number of the newly set control point being less than the number of the plurality of control points.