Segmented Phase Plug for Uniform Loudspeaker Directivity
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Solution Overview
Problem
Automotive sound systems face issues with varying tonal balance due to the directivity characteristics of direct radiating loudspeakers, resulting in different frequency responses for listeners depending on their position, with existing solutions failing to provide uniform sound quality across different listening positions.
Innovation Solution
The use of a phase plug with multiple spaced slots to guide sound energy from the loudspeaker's diaphragm, which radiates sound into an ambient environment without a horn, providing low and uniform directivity over a wide frequency range by minimizing nulls in the response at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct radiating loudspeaker is used, then the structure is simple and cost-effective, but the directivity is high causing non-uniform tonal balance at different listening positions
Solution Approach 1:
The loudspeaker diaphragm is segmented into a central phase plug portion and a surrounding annular radiator portion. The phase plug portion fills the acoustic short circuit between the front and back of the diaphragm, while the annular radiator provides the main sound radiation. This segmentation allows the system to maintain simple structure while achieving improved directivity control and uniform tonal balance across different listening positions.
2Ease of manufacture
If the diaphragm area is reduced to lower directivity, then uniform sound radiation is achieved, but the sound producing surface area is insufficient
Solution Approach 1:
The diaphragm is divided into two functional zones: the phase plug portion (central area) that fills acoustic short circuits and the annular radiator portion (surrounding area) that radiates sound. This allows the total diaphragm area to remain large for sufficient sound production while the effective radiating area is controlled to achieve desired directivity characteristics.
Solution Approach 2:
The phase plug acts as an intermediary element that fills the acoustic short circuit between the front and back of the diaphragm. It has acoustic impedance matching characteristics that allow it to transfer acoustic energy from the back of the diaphragm to the front without creating direct short circuits, thereby improving efficiency while controlling directivity.
3Ease of manufacture
If sound energy is guided through a smaller aperture, then directivity is reduced and uniformity is improved, but nulls appear in the frequency response at higher frequencies
Solution Approach 1:
By segmenting the diaphragm into phase plug and annular radiator portions, the system achieves a larger effective radiating area compared to using only a small central aperture. This segmentation allows sound energy to be distributed more evenly across the frequency spectrum, reducing the formation of nulls while maintaining improved directivity control.
Solution Approach 2:
The phase plug portion changes the acoustic impedance parameters in the central region, creating a gradient that matches the acoustic transition from the back to the front of the diaphragm. This parameter change allows for broader frequency response by preventing the formation of sharp nulls that would occur with a simple small aperture, while still achieving the desired directivity reduction.
Data Source
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AI summary
A phase plugs or acoustic lens improves the directional audio performance of a loudspeaker. Application of the improved directional audio performance to a sound system in a listening area improves the performance of the audio system. Configurations of acoustic lens or phase plug which include both symmetrical and asymmetrical features to provide an improved frequency response and directivity are presented. The application of phase plugs or acoustic lens to a loudspeaker may provide improved sound in a listing location, for example, in a vehicle.