Loudspeaker Array FIR Filter Design for Directivity Control
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Solution Overview
Problem
Existing multi-way loudspeaker systems face challenges in achieving smooth, frequency-independent sound responses across a large area due to physical driver spacing and phase distortion issues, particularly outside the acoustic center, and are limited by the use of specific driver types and logarithmic spacing designs.
Innovation Solution
A multi-way loudspeaker system with a line array configuration featuring digitally controlled FIR filters and power D/A converters, where drivers of various sizes are arranged in sealed compartments to minimize coupling, and a filter design algorithm adjusts driver positions and coefficients to achieve optimal frequency response and directivity using a cost minimization function and Fourier approximation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple specialized drivers are used for dedicated frequency bands, then sound quality is improved, but driver spacing causes frequency response distortion outside the acoustic center
Solution Approach 1:
The system divides the audio frequency spectrum into multiple dedicated bands, with each driver (tweeter, midrange, woofer) handling a specific frequency range. This segmentation allows each driver to operate optimally within its designated band, improving overall sound quality while managing the complexity of driver interactions through structured frequency separation.
Solution Approach 2:
The patent employs digital signal processing with FIR filters to dynamically adjust the frequency response parameters across different listening positions. By changing the digital filter parameters based on position detection, the system compensates for interference distortion that occurs outside the acoustic center, maintaining frequency response accuracy throughout the listening area.
2Ease of operation
If logarithmically spaced transducer arrays are used, then directivity control is improved, but design is restricted to full-range drivers and public address systems
Solution Approach 1:
The system creates a universal loudspeaker design that can accommodate multiple driver types (tweeters, midrange drivers, woofers) in addition to full-range drivers. The logarithmic spacing framework is made adaptable through digital signal processing that can handle different driver characteristics, allowing the same physical configuration to serve multiple application types including high-fidelity audio and public address systems.
Solution Approach 2:
The patent uses digital filtering and signal processing parameters to adapt the logarithmically spaced array to work with various driver types. By changing the digital processing parameters rather than the physical configuration, the system maintains optimal directivity control while becoming versatile enough to handle different driver specifications and application requirements.
3Manufacturing precision
If very steep brick-wall FIR filters are applied, then transition band errors are reduced, but individual driver polar responses create audible discontinuities
Solution Approach 1:
The system incorporates position detection and adaptive digital signal processing that provides feedback about the listener's location. Based on this feedback, the FIR filter parameters are dynamically adjusted to compensate for polar response variations across different listening positions. This feedback mechanism smooths out the discontinuities that would otherwise be audible when using steep brick-wall filters.
Solution Approach 2:
Rather than using fixed static filters, the patent implements dynamic digital filtering where the FIR filter coefficients are adjusted in real-time based on listening position and frequency content. This dynamic approach allows the system to maintain smooth frequency responses across different polar angles by adapting the filter characteristics to compensate for individual driver polar response variations.
4Ease of manufacture
If drivers are spaced according to physical dimensions, then manufacturing is simplified, but out-of-axis aberrations cannot be completely avoided
Solution Approach 1:
The patent introduces digital signal processing as an intermediary between the physical driver spacing and the acoustic output. The FIR filters and DSP algorithms compensate for the aberrations caused by fixed physical spacing, allowing manufacturers to use practical driver dimensions while still achieving accurate out-of-axis responses through digital correction.
Solution Approach 2:
The system changes the electrical and digital parameters (filter coefficients, gain, phase) to compensate for the fixed physical spacing of drivers. By adjusting these controllable parameters, the patent maintains manufacturing simplicity while achieving precise acoustic performance across different listening positions, effectively decoupling manufacturing constraints from acoustic performance requirements.
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 system provides high-quality sound with low distortion and controlled out-of-axis responses, capable of suppressing reflections and maintaining performance across both vertical and horizontal planes, allowing for compact, versatile installation in surround sound systems.
Implementation Method 1
Each signal path comprises digital input and contains a digital FIR filter and a power D/A converter
Implementation Method 2
Each signal path comprises digital input and contains a digital FIR filter and a power D/A converter
Implementation Method 3
having sealed compartments that separate certain drivers from one another to prevent coupling of the drivers
Implementation Method 4
The system provides high-quality sound with low distortion and controlled out-of-axis responses, capable of suppressing reflections and maintaining performance across both vertical and horizontal planes
Data Source
AI summary
The invention is a multi-channel loudspeaker system that provides a compact loudspeaker configuration and filter design methodology that operates in the digital signal processing domain. Further, the loudspeaker system can be designed to include drivers of various physical dimensions and can achieve prescribed constant directivity over a large area in both the vertical and horizontal planes.