Sound Field Planarity Control for Acoustic Zone Separation
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Solution Overview
Problem
Existing sound zone control methods face challenges in achieving excellent acoustic contrast between target and dark zones while maintaining phase control and avoiding self-cancellation artefacts, often requiring high array effort and being limited by spatial aliasing issues, especially at higher frequencies.
Innovation Solution
A novel cost function, 'planarity control', constrains the incoming plane wave direction within a range of angles to optimize sound field planarity and cancellation, using a weighting matrix to control the energy distribution in the target zone, allowing the system to find the best plane wave direction and minimizing effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If energy cancellation methods are used to create dark zones, then acoustic contrast between zones is improved, but phase control in the target zone deteriorates leading to self-cancellation artefacts
Solution Approach 1:
The patent merges two previously separate optimization objectives into a single unified cost function. The cost function simultaneously optimizes for acoustic contrast (energy cancellation in dark zone) and phase control (planarity in target zone) by combining their respective mathematical formulations. This integration allows the system to achieve both excellent cancellation and controlled phase behavior without the trade-offs of separate optimizations.
Solution Approach 2:
The patent introduces a new parameter - the planarity measure - that quantifies the uniformity of sound pressure across the target zone. By adding this parameter to the optimization framework, the system can directly control phase behavior and avoid self-cancellation artefacts. The cost function incorporates this parameter with appropriate weighting to balance contrast and planarity requirements.
2Reliability
If synthesis approaches are used to control sound fields, then phase control and homogeneity are improved, but acoustic contrast and array effort deteriorate
Solution Approach 1:
The unified cost function merges the strengths of both synthesis and cancellation approaches. It incorporates the planarity measure from synthesis methods (which ensures phase control and homogeneity) while simultaneously including the acoustic contrast objective from cancellation methods (which ensures energy attenuation in dark zones). This combination allows the system to achieve both good phase control and high acoustic contrast.
3Stability of the object's composition
If plane wave specification is used for target zone, then sound field homogeneity is improved, but spatial aliasing limits high frequency reproduction
Solution Approach 1:
The patent applies dynamic optimization that adapts to frequency content. The planarity measure and cost function are evaluated and optimized across the frequency spectrum, allowing the system to maintain sound field homogeneity at frequencies below the spatial aliasing limit while gracefully degrading or adjusting behavior at higher frequencies where aliasing becomes problematic. This frequency-dependent optimization enables robust performance across a wide bandwidth.
4Manufacturing precision
If acoustic contrast optimization is prioritized, then cancellation performance is improved, but control effort increases
Solution Approach 1:
The patent introduces the planarity measure as an additional optimization parameter that works synergistically with acoustic contrast. By optimizing for both contrast and planarity simultaneously through the unified cost function, the system achieves effective cancellation with reduced control effort. The planarity constraint helps guide the optimization toward solutions that are physically realizable and energy-efficient, preventing excessive control effort while maintaining cancellation performance.
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
The planarity control method achieves excellent cancellation and sound field planarity across a wide frequency range, outperforming existing methods in contrast and control effort, and effectively reduces self-cancellation artefacts, with robust performance above the spatial aliasing limit.
Implementation Method 1
Fundamentally, at least two kinds of region must be created by the loudspeaker array - the target zone, where the sound pressure reaches a certain target level, and the dark zone, a region of cancellation where the audio programme delivered to the target zone is attenuated
Data Source
AI summary
A method of deriving parameters for sound output into a space having a target zone and a dark zone. Sound may be desired output into the target zone but not into the dark zone. The parameters are optimized so that the sound within the target zone is planar and homogeneous, but the direction of arrival is allowed to vary within a predetermined range, so that the parameters may be optimized in a more suitable manner.