Line Array Speaker Delay Control Using FIR Filters
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Solution Overview
Problem
Existing speaker devices with line array speakers face challenges in controlling very small delays less than the sampling period without significantly increasing calculation load, which affects the formation of a uniform sound field over a wide range.
Innovation Solution
The use of FIR filters to delay digital sound signals, combined with D/A converters and filter coefficient storage, allows for precise control of delay time differences between speakers, enabling the formation of a desired sound field even on a flat plate front panel, with optional IIR filters for amplitude and phase control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital signal processing is used to provide delay less than the sampling period, then the desired curved sound field can be formed, but the calculation load becomes excessive
Solution Approach 1:
The delay function is segmented into two parts: a large delay component implemented using standard digital signal processing techniques, and a small delay component (less than sampling period) implemented using a specialized circuit that operates in parallel. This segmentation allows the majority of the delay to be handled by efficient software algorithms while only a small correction is made by the dedicated hardware circuit, significantly reducing the overall calculation load requirement.
Solution Approach 2:
A dedicated delay circuit is introduced as an intermediary component between the digital signal processor and the speakers. This circuit specifically handles the small delay portions (less than sampling period) that cannot be accurately achieved through digital processing alone. By using this intermediary hardware component, the digital signal processor is relieved of the burden of computing extremely precise delays, thereby reducing its calculation load.
2Device complexity
If linear interpolation is used to provide small delay, then the calculation load is reduced, but reproducibility in high range is considerably reduced
Solution Approach 1:
A dedicated delay circuit serves as an intermediary that handles the small delay portions (less than sampling period) with high precision. This circuit uses hardware-based timing mechanisms rather than software interpolation, ensuring accurate delay control even at high frequencies where interpolation would fail. The digital signal processor works in conjunction with this intermediary to provide both the delay function and high-frequency fidelity.
3Manufacturing precision
If oversampling and linear or polynomial interpolation are combined, then small delay can be provided, but a low pass filter with sharp cutoff is required which makes calculation load excessive
Solution Approach 1:
The delay system is segmented such that the majority of the delay (integral multiples of sampling period) is handled by the digital signal processor using efficient algorithms, while only a small delay portion is handled by the dedicated circuit. This segmentation eliminates the need for oversampling and complex interpolation filters, as the dedicated circuit can handle the remaining small delay without requiring sharp cutoff filtering.
Solution Approach 2:
The dedicated delay circuit acts as an intermediary that handles the small delay portions without requiring subsequent filtering. By using hardware-based timing mechanisms, the circuit can provide precise delay control directly without needing to compensate for interpolation artifacts through sharp cutoff low pass filters, thereby eliminating the excessive filter processing load.
Data Source
AI summary
To provide a speaker device that can form a substantially uniform sound field over a range from a long distance to a short distance without significantly increasing a calculation load. A plurality of FIR filters 21 to 2n perform delay control of respective speakers so as to increase a delay time difference between adjacent speakers 51 to 5n in a line array speaker 5 toward one end of the line array speaker 5, and thereby over a wide range from a long distance to a short distance, a sound filed 12 is formed. Also, by adding a common shift delay time Dc to filter coefficients for the FIR filters 21 to 2n, the delay time difference between adjacent speakers 51 to 5n is made less than a sampling period of a sound signal to form a wide and uniform sound field 12.