Sound Field Generator Using Dual Modulation for Noise Cancellation
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Solution Overview
Problem
Conventional sound field generation apparatuses face challenges in making sounds within a specific range easily audible and are costly due to the use of multiple ultrasonic wave elements and carrier frequencies, leading to noise interference.
Innovation Solution
A sound field generation apparatus that employs two modulation units with different modulation systems for ultrasonic waves and a filter unit to cancel audible sounds at a control point outside the sound field, using the same type of ultrasonic wave elements to reduce noise and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If two carrier frequencies are used to suppress sound propagation, then sound directionality is improved, but noise from frequency differences is caused and cost increases
Solution Approach 1:
The patent converts the harmful noise effect into a beneficial cancellation effect. By using two different modulation systems (AM and FM) with the same carrier frequency, the patent generates two audible sounds that can be made equal in amplitude and opposite in phase at the control point, causing destructive interference that suppresses sound propagation in the rear direction while eliminating frequency difference noise
Solution Approach 2:
The patent changes the modulation parameters (amplitude and phase) of the two audible sounds generated by different modulation systems. By adjusting these parameters through filter characteristics, the patent makes the amplitudes equal and phases opposite at the control point, achieving sound suppression without requiring different carrier frequencies
2Object-affected harmful factors
If two carrier frequencies are used to suppress sound propagation, then sound directionality is improved, but device cost increases
Solution Approach 1:
The patent uses the same carrier frequency for both modulation systems, which allows the use of identical ultrasonic wave elements (same type of transducers). This homogeneity in frequency parameters translates to cost reduction by eliminating the need for different types of expensive ultrasonic wave elements that would be required if different carrier frequencies were used
3Device complexity
If ultrasonic waves are amplitude-modulated by the same sound signal, then modulation is simplified, but sound in specific area is weakened
Solution Approach 1:
The patent segments the single modulation process into two different modulation systems (AM and FM) operating with the same carrier frequency. This segmentation allows independent control of the modulation characteristics, enabling the system to generate two distinct audible sounds that can be optimized for different spatial regions, thereby strengthening sound in specific areas while maintaining manageable complexity
Data Source
AI summary
A sound field generation apparatus includes: a first modulation unit modulating an ultrasonic wave signal according to a prescribed modulation system; a second modulation unit modulating the ultrasonic wave signal according to a modulation system different from the modulation system of the first modulation unit; a filter unit changing frequency characteristics of an audible range signal used in modulation of the second modulation unit; a first ultrasonic wave output unit outputting a first ultrasonic wave signal modulated by the first modulation unit; and a second ultrasonic wave output unit outputting a second ultrasonic wave signal modulated by the second modulation unit, wherein the filter unit is set to have filter characteristics to cancel a first audible sound reproduced by the first ultrasonic wave signal with a second audible sound reproduced by the second ultrasonic wave signal at a control point provided outside the sound field.