Loudspeaker Crossover Filters for Off-Axis Response Flatness
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Solution Overview
Problem
Multi-way loudspeaker systems with non-coincident drivers face challenges in achieving a flat or smooth acoustic frequency response across an area due to the required spacing between drivers, leading to interference and deviations from desired frequency curves, despite previous attempts with Linkwitz-Riley, Chebychev, FIR, and d'Appolito filtering methods.
Innovation Solution
A method for computing frequency responses of crossover filters by setting an attenuation factor for sound pressure levels, using a point source model to determine crossover frequencies, and iteratively designing filters in the audible frequency range, low frequency band, and high frequency band to minimize distortion and achieve uniform frequency responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If drivers are spaced apart due to their physical size, then each driver can operate within its designed frequency band, but interferences occur due to different path lengths of sound waves traveling from the drivers to the considered point in space
Solution Approach 1:
The patent applies parameter changes by modifying the crossover filter characteristics (order, type, frequency points) to compensate for the interference caused by driver spacing. Different crossover filter parameters are used to achieve flat frequency responses at specific listening positions despite the fixed physical spacing between drivers.
2Reliability
If 4th order Linkwitz-Riley crossover filters are used to divide frequency bands, then drivers work within their designed frequency bands, but large deviations from flat response curves occur out of the main axis due to interferences around crossover points
Solution Approach 1:
The patent changes the crossover filter parameters (order, type, frequency points) to achieve flat frequency responses. Instead of universally using 4th order Linkwitz-Riley filters, the patent applies different filter parameters (e.g., 2nd order Butterworth, 4th order Chebychev, or other types) depending on the specific listening position requirements and driver configuration.
Solution Approach 2:
The patent applies local quality by optimizing crossover filter characteristics for specific listening positions (on-axis vs. off-axis). Different filter parameters are selected to achieve flat responses at different spatial locations, recognizing that a single filter design cannot optimally serve all listening positions simultaneously.
3Manufacturing precision
If 4th order Chebychev filters with prescribed stopband attenuation and flat passband are used, then error regions are narrowed, but deviation still exists around the crossover points and does not achieve desired flat frequency responses over the desired area
Solution Approach 1:
The patent applies local quality by designing different crossover filter characteristics for different spatial regions. Filters are optimized to provide flat responses at specific listening positions while accepting that other positions may experience variations. This position-specific optimization approach allows achieving flat responses in targeted areas rather than uniformly across all space.
Data Source
AI summary
A method is provided for computing frequency responses of crossover filters for multi-way loudspeakers. The method prescribes driver coordinates for drivers in the multi-way loudspeaker, prescribes an attenuation function for the sound pressure level at a desired angle, computes the crossover frequencies using a point source model and computes the frequency responses in intervals defined by the crossover frequencies.