Nested Loudspeaker Asymmetry Mitigates Diffraction
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Solution Overview
Problem
Conventional compound loudspeakers suffer from acoustical mismatches between high and low frequency diaphragms, leading to diffraction and comb-filter effects that degrade high frequency radiation characteristics due to radial discontinuities and acoustical coupling issues.
Innovation Solution
A new compound loudspeaker driver design featuring a radially irregular discontinuity on the forward face, where the distance between the acoustic center axis and the functional edge of the outer driver varies non-constantly in different radial directions, reducing diffraction and maintaining smooth frequency responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the high frequency diaphragm is elevated forward from the low frequency cone neck, then the axial movement of the voice coil is enabled, but the radiation of the high frequency diaphragm is directed rearwards towards the low frequency cone and reflected back forward causing comb-filter effect
Solution Approach 1:
The invention applies asymmetry by positioning the high frequency diaphragm off the acoustic center axis of the low frequency driver. This asymmetric placement prevents the high frequency radiation from being symmetrically reflected back by the cone, thereby eliminating the comb-filter effect while maintaining axial movement capability through proper clearance design
2Ease of operation
If a circular gap is left between the cone and the high frequency driver annular baffle, then axial movement of the low frequency cone is allowed, but significant diffraction occurs on the frontal radiation axis in the frequency range between 2 kHz and 20 kHz
Solution Approach 1:
The invention replaces the circular (symmetric) gap with a non-circular, irregularly shaped gap that extends preferentially in the vertical direction. This asymmetric geometry prevents simultaneous arrival of diffracted sound waves at the listener position, thereby reducing diffraction effects while preserving the necessary axial movement clearance
3Ease of operation
If the outer flexible surround is made radial to allow cone movement, then the cone can move axially, but the surround generates acoustical mismatch resulting in radial diffraction at different frequencies
Solution Approach 1:
The invention modifies the surround geometry from a radially symmetric configuration to an asymmetric one where the surround extends more in the vertical direction than horizontally. This asymmetric shape prevents simultaneous diffraction of sound waves in all radial directions, reducing the acoustical mismatch and radial diffraction effects while maintaining cone movement capability
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 design mitigates frequency response impairments by minimizing diffraction, ensuring smooth on- and off-axis frequency responses and reducing axial excursions' impact on sound quality.
Implementation Method 1
a significant diffraction typically occurs on the frontal radiation axis of the system. The frequency range of such diffraction is typically between 2 kHz and 20 kHz
Data Source
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AI summary
A nested compound loudspeaker comprising a speaker assembly chassis (11), an outer driver (18) connected to the speaker assembly chassis (11) and having an inner edge, which defines an opening in the outer driver (18) and forms a functional edge (20), and an inner driver (8) connected to the speaker assembly chassis (11) and at least partially surrounded by the opening of the outer driver (18) and the inner driver (8) having an acoustical centre axis located at a distance (r) from the functional edge (20) in a radial direction (a). The distance (r) is non-constant around the acoustical centre axis, wherein the distance (r) has a first value in a first radial direction (a) and a second value different to the first value in a second radial direction (a).