Ultrasonic Loudspeaker Enclosure Phase Control for Secondary Lobe Reduction
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Solution Overview
Problem
Existing directional loudspeaker enclosures using acoustic nonlinearity to convert ultrasounds to audible sound face issues with reduced ultrasound carrier levels only at the center of the beam, leading to uncomfortable listening conditions and increased secondary lobes, which can expose listeners to undesirable ultrasound levels.
Innovation Solution
A loudspeaker enclosure with at least two ultrasound sources that apply distinct gains and phase shifts to different frequency components of the supply signals, allowing for better control of the ultrasound beam and reduction of secondary lobes, thereby widening the listening area and managing exposure to ultrasound waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ultrasound carrier level is reduced at the center of the beam, then audible sound quality is improved, but secondary lobes increase causing excessive ultrasound exposure
Solution Approach 1:
The patent applies different phase shifts to different spatial regions of the ultrasound beam. Specifically, it modifies the phase of ultrasound carriers in secondary lobes differently from the main beam center, allowing localized control of ultrasound exposure. This enables reduction of harmful secondary lobes while preserving audible sound quality in the listening area.
Solution Approach 2:
The patent changes the phase parameter of ultrasound carrier signals dynamically. By applying frequency-dependent phase shifts to different sources, it transforms the ultrasound beam pattern, reducing energy in secondary lobes while maintaining the main beam structure for audible sound generation.
2Object-affected harmful factors
If phase cancellation is applied to reduce carrier level, then audible demodulated levels are maintained, but the listening area becomes limited to the beam center
Solution Approach 1:
The patent introduces dynamic phase shifting that adapts to different spatial positions and frequencies. Unlike fixed phase cancellation, the phase shifts are adjusted based on the desired listening area requirements, allowing the system to dynamically expand or contract the effective listening zone while maintaining carrier level control.
Solution Approach 2:
The patent extends the control from simple amplitude modulation to include phase dimension control. By manipulating phase across multiple frequency components and spatial positions, it creates additional degrees of freedom for shaping the listening area, transforming a 1D amplitude problem into a multi-dimensional phase-amplitude control problem.
3Adaptability or versatility
If secondary lobes are increased to expand listening area, then more listeners can be accommodated, but ultrasound exposure levels become undesirable
Solution Approach 1:
The patent segments the ultrasound beam into distinct spatial regions (main beam and secondary lobes) and applies independent phase control to each. This allows selective manipulation of energy distribution, enabling expansion of the listening area through controlled secondary lobe formation while maintaining safe ultrasound exposure levels through phase-based energy redirection.
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 solution enhances the control over the main and secondary lobes of the ultrasound beam, reducing exposure to high ultrasound levels while maintaining sound quality, and allows for adaptable listening areas based on listener position, ensuring compliance with exposure guidelines.
Implementation Method 1
The acoustic nonlinearity properties of air make it possible to recreate audible sound from only ultrasounds. Indeed, when two ultrasound waves, emitted at a high sound level (typically above 100 dB), propagate in the air, they interact with each other by converting a part of their energy to form two new waves whose frequencies are, on the one hand, the difference between the two ultrasound frequencies and, on the other hand, the sum between the two ultrasound frequencies.
Implementation Method 2
This nonlinear phenomenon, occurring in the air, is called 'self-demodulation'. This acoustic effect occurs at each point of the ultrasound beam emitted by the loudspeaker as long as the residual energy of the ultrasound waves is high enough to generate it.
Implementation Method 3
By adding a second, independent, ring-shaped emitting surface about the circular surface, so that the two surfaces have the same surface area, it is possible to modulate the signals to be transmitted with two carriers of same frequency but different phases on each surface. Hence, by suitably choosing the phase of the carrier emitted on the ring surface, the two carriers interact destructively at a certain distance of propagation and cancel each other.
Data Source
AI summary
Disclosed is a loudspeaker enclosure including: —at least two sources suitable for producing ultrasound signals, and—a supply designed to process and amplify at least one input signal so as to produce, for the sources, supply signals of the same frequency and of different phases, wherein the supply are configured to apply different gains and/or phase shifts to at least two different frequency components of at least one of the supply signals. Also disclosed is a method for signal modulation for such an ultrasonic loudspeaker enclosure.