Local Sound Field Synthesis via Virtual Scattering Body
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Solution Overview
Problem
Existing sound field synthesis methods, such as stereophony, wave field synthesis, and ambisonics, face limitations in achieving accurate spatial sound reproduction beyond a limited 'sweet spot' due to finite loudspeaker arrangements, leading to artifacts across the listening area.
Innovation Solution
The method combines sound field synthesis with time-reversal acoustics, using a virtual scattering body to recreate the desired sound field within a local area by time-reversing signals from loudspeakers outside the listening area, allowing for improved accuracy and flexibility in sound field reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If wave field synthesis is used to extend the listening area, then the sweet spot is enlarged, but large deviations and aliasing artifacts occur over the entire listening area due to finite loudspeaker spacing
Solution Approach 1:
The patent divides the listening area into a local target area and surrounding regions. By segmenting the sound field synthesis problem, the system achieves high accuracy within the target area while managing artifacts in surrounding regions through controlled scattering bodies.
Solution Approach 2:
The patent applies different quality requirements to different spatial regions. The local target area receives high-precision sound field reconstruction, while surrounding areas tolerate controlled artifacts. This is achieved by positioning scattering bodies to confine accurate reproduction to the desired local region.
2Ease of manufacture
If ambisonics with circular or spherical speaker arrangements is used, then analytical calculation of loudspeaker signals is enabled, but the sweet spot is restricted to the center of the speaker array
Solution Approach 1:
The patent makes the listening area dynamically positionable within the loudspeaker array by adjusting the parameters of the virtual scattering body. This allows the sweet spot to be moved to different locations while maintaining analytical calculation capabilities.
Solution Approach 2:
The patent uses a virtual scattering body as a mathematical model to represent the desired sound field configuration. This virtual copy allows flexible positioning of the sweet spot without requiring physical reconfiguration of the loudspeaker array.
3Loss of information
If generalized sound field synthesis methods are used to solve the synthesis equation explicitly, then insight into synthesis mechanisms is gained, but the method becomes numerically expensive and ill-conditioned
Solution Approach 1:
The patent transforms the complex general synthesis equation into a simplified form by introducing specific parameters for the virtual scattering body (position, size, shape). This parameterization reduces computational complexity while preserving the essential synthesis mechanisms.
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 enables more accurate sound field reconstruction within a local, dynamically placed listening area with reduced artifacts, supporting both circular and linear speaker arrangements and allowing for the creation of quiet zones or reduced sound pressure areas.
Implementation Method 1
the external sound field of a system for sound field synthesis corresponds to the scattering of the desired sound field at the contour of the system
Implementation Method 2
The corresponding acoustic boundary conditions must now be synthesized at the edge of the local audience area. This could, for example - similar to the method from the above-mentioned publication by F.M. Fazi et al. - done by an explicit solution of the underlying integral equations. However, this requires complex mathematical calculations. According to the present invention, the principles of time-reversal acoustics are used for this purpose.
Data Source
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AI summary
The method involves determining a virtual sound field outside the listener area, which is created by scattering a desired sound field at a virtual scattering body with geometry equivalent to the geometry of the listener area. The signals of the scattered virtual sound field are determined at the positions of the speakers, where the time signals of the virtual sound field are reversed. The speakers are arranged in a circular, linear, rectangular, oval or spherical form, where the amplitudes of the speaker signals are corrected. Independent claims are included for the following: (1) a method for reproducing a desired sound field inside a local area by multiple speakers at positions outside the listener area; and (2) a method for generating a quiet zone or a zone with reduced sound pressure in a sound field.