Piezo Diaphragm Speaker Feedback for Flat Audio Response
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Solution Overview
Problem
Piezo diaphragms exhibit non-flat frequency response with significant peaks and valleys, causing audio signal distortion and limiting their use in applications requiring high-quality audio, such as music or human voice, due to their relatively low cost and suitability for tone-based applications like alarms or buzzers.
Innovation Solution
A self-drive type piezo diaphragm configuration with a plate and two piezo films, where the first film converts audio signals into motion and the second film converts this motion into an electrical signal for feedback, achieving a flat frequency response through kinetic coupling, allowing the diaphragm to function as both a speaker and a microphone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a voice coil motor is used as the actuator, then the driving force is sufficient, but the structure becomes complex and high-frequency response is difficult to achieve
Solution Approach 1:
The patent replaces the voice coil motor (electromagnetic actuator) with a piezoelectric actuator that utilizes piezoelectric expansion/contraction of a stack component. This substitution eliminates the need for complex electromagnetic components while achieving sufficient driving force and enabling high-frequency response up to 20 kHz or higher.
Solution Approach 2:
The patent changes the actuation mechanism from electromagnetic force generation to piezoelectric dimensional change. The piezoelectric stack expands and contracts in response to applied voltage, directly driving the diaphragm without the mechanical complexity of voice coil assemblies, thereby achieving both sufficient force and high-frequency response.
2Force
If a voice coil motor is used, then driving force is adequate, but high-frequency response above 20 kHz cannot be achieved
Solution Approach 1:
The patent replaces the voice coil motor with a piezoelectric actuator system that can respond to high-frequency signals. The piezoelectric stack's direct coupling to the diaphragm and absence of electromagnetic inertia enables frequency response extending to 20 kHz or higher while maintaining adequate driving force through the piezoelectric effect.
Solution Approach 2:
The patent utilizes the piezoelectric stack's ability to vibrate at high frequencies directly coupled to the diaphragm. The piezoelectric material's rapid response to alternating voltage enables the system to reproduce high-frequency sounds up to 20 kHz or higher, overcoming the bandwidth limitations of voice coil motors.
3Device complexity
If an electromagnetic actuator is used, then the driving mechanism is simple, but distortion occurs due to non-linear magnetic flux density changes
Solution Approach 1:
The patent substitutes the electromagnetic actuator with a piezoelectric actuator that avoids magnetic flux density variations entirely. The piezoelectric stack's dimensional changes are directly proportional to applied voltage, eliminating the non-linear magnetic effects that cause distortion and improving signal fidelity without sacrificing structural simplicity.
4Speed
If the diaphragm is directly coupled to the actuator, then high-frequency response is improved, but resonance occurs due to loose coupling at low frequencies
Solution Approach 1:
The patent applies different coupling characteristics to different frequency ranges through the compliance member. The compliance member provides flexible, resonance-damped coupling at low frequencies while maintaining effective force transmission, and enables direct coupling benefits at high frequencies where resonance is less problematic, thus achieving stable coupling across the full frequency spectrum.
Solution Approach 2:
The patent employs a compliance member with specific elastic properties that combines the benefits of flexible coupling and rigid force transmission. This composite approach uses materials and structures that adapt their effective stiffness based on frequency, providing stable low-frequency coupling while enabling high-frequency response.
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
The configuration results in a substantially flat frequency response within the audio frequency band, enabling high-quality audio signal generation while maintaining a small form factor and significantly reducing costs compared to traditional piezo speakers.
Implementation Method 1
a piezoelectric stack which expands and contracts in accordance with an applied signal
Implementation Method 2
a compliant member having an elastic force; a diaphragm which is driven by the compliant member
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
An audio speaker system includes: an amplifier, where a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node; and a piezo diaphragm including: a metal plate; a first piezo film attached to the metal plate, where the first piezo film is configured to function as a speaker during operation of the audio speaker system; and a second piezo film attached to the metal plate and spaced apart from the first piezo film, where the second piezo film is configured to function as a microphone during operation of the audio speaker system, where an output terminal of the amplifier is coupled to the first piezo film, and where a negative input terminal of the amplifier is coupled to the second piezo film.