Stereo Imaging Layout for Directional Compact Speakers
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Solution Overview
Problem
Existing audio playback systems face limitations in achieving wide stereo imaging, particularly at low and mid-frequencies, and struggle with directionality issues due to the inherent characteristics of side-firing and forward-firing transducers.
Innovation Solution
A combination of partial-direct and partial-dipole reproduction of stereo signals is achieved by up-mixing left and right channels to generate a center audio signal, filtering mid-frequency bands, and using side-firing and forward-firing transducers to output ambient and direct components, respectively, while employing obstruction detection and steering techniques to optimize output directionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If side-firing transducers are used to achieve wide stereo imaging, then spatial width is improved, but directionality deteriorates at low and mid-frequencies
Solution Approach 1:
The audio signal is segmented into different frequency bands (low, mid, high frequencies), and each band is processed differently. Low and mid-frequency signals are routed to forward-firing transducers for directional reproduction, while high-frequency signals are routed to side-firing transducers for spatial width, resolving the contradiction between stereo image width and directionality across the frequency spectrum.
Solution Approach 2:
Different frequency ranges are assigned different spatial characteristics: low and mid-frequencies are reproduced with directional quality from forward-firing transducers, while high-frequencies are reproduced with omnidirectional quality from side-firing transducers. This local quality differentiation allows each frequency band to optimize its spatial reproduction characteristics.
2Measurement precision
If forward-firing transducers are used to achieve directionality, then directionality is improved, but stereo image width deteriorates
Solution Approach 1:
The frequency spectrum is segmented into low/mid-range and high-range components. Forward-firing transducers handle low and mid-frequencies to provide directionality, while side-firing transducers handle high-frequencies to provide stereo image width, allowing both requirements to be satisfied simultaneously in their respective frequency domains.
Solution Approach 2:
The solution adds a frequency dimension to the spatial reproduction problem. Instead of trying to achieve both directionality and width at all frequencies, the system uses frequency as an additional dimension to differentiate the spatial characteristics of different transducer types, with forward-firing transducers providing directional low/mid-bass and side-firing transducers providing omnidirectional high-frequency content.
3Volume of moving object
If compact speaker design is used, then device size is reduced, but spatial imaging capability deteriorates due to omnidirectional reproduction at frequencies where wavelength exceeds device dimensions
Solution Approach 1:
The audio frequency spectrum is segmented into low/mid-frequencies and high-frequencies. Compact speakers use forward-firing transducers for low and mid-frequencies to maintain directionality and spatial imaging, while using side-firing transducers for high-frequencies where the compact size naturally provides sufficient directionality, thus maintaining spatial imaging capability despite reduced device dimensions.
Solution Approach 2:
The system changes the operational parameters of the transducers by frequency: directionality is maintained at low and mid-frequencies through forward-firing configuration, while at high-frequencies the side-firing configuration provides adequate directionality despite the compact form factor, allowing the device to maintain spatial imaging across its size-constrained design.
Data Source
AI summary
Example techniques relate to stereo imaging with audio playback devices. Example playback devices described herein may include multiple speakers, such as a forward-firing audio transducer and side-firing audio transducers. Using example techniques, such playback devices may play stereo content partially directly and partially as a dipole, which may enhance (e.g., widen) a stereo image formed by the transducers. Yet further, such techniques may be combined with steering techniques to direct output of the transducers away from obstructions that may be present in proximity to the audio playback devices.