Audio Distortion Reduction via Capacitive Diaphragm Displacement Feedback
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Solution Overview
Problem
Loudspeakers, especially small ones in portable devices, suffer from distortion due to non-proportional diaphragm movement caused by varying magnetic fields and springiness, leading to loss of acoustical fidelity.
Innovation Solution
An audio system measures a test current through the loudspeaker to determine its capacitance, using this feedback to adjust the target audio signal and reduce distortion by generating a feedback signal that represents actual diaphragm displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a loudspeaker is made small for portable devices, then the device size is reduced, but audio distortion increases due to non-proportional diaphragm movement
Solution Approach 1:
The patent applies feedback by measuring the actual diaphragm displacement using a capacitive sensor and comparing it to the target displacement from the audio signal. The difference (distortion) is fed back to a correction circuit that generates a compensating signal to adjust the voice coil drive, thereby reducing distortion and improving audio fidelity in small loudspeakers
Solution Approach 2:
The patent replaces direct mechanical measurement of diaphragm position with an electrical measurement system. A capacitive sensor converts mechanical displacement into an electrical signal that can be processed electronically, enabling precise measurement and feedback control without adding mechanical complexity to the small loudspeaker system
2Device complexity
If the magnetic field interaction varies with coil position, then the loudspeaker structure is simpler, but distortion increases due to non-constant magnetic field effects
Solution Approach 1:
The patent uses feedback to measure the actual diaphragm position and the resulting distortion caused by varying magnetic field interaction. The feedback signal is used to generate a correction that compensates for the non-constant magnetic field effects, maintaining accurate diaphragm movement without requiring complex magnetic field control mechanisms
Solution Approach 2:
The patent employs a capacitive sensor that automatically tracks the diaphragm position and provides real-time feedback about the actual displacement. This self-measuring system continuously monitors the distortion caused by magnetic field variations and enables automatic correction without external intervention or complex control mechanisms
3Device complexity
If the suspension springiness varies with diaphragm displacement, then the loudspeaker construction is simpler, but distortion increases due to non-linear mechanical response
Solution Approach 1:
The patent measures the actual diaphragm displacement using a capacitive sensor and compares it to the target displacement. The feedback signal captures distortion caused by non-linear suspension springiness, and a correction circuit generates a compensating signal to adjust the voice coil drive, thereby linearizing the frequency response without requiring a complex suspension system
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 system increases audio fidelity by ensuring the loudspeaker's displacement more accurately matches the target audio signal, thereby reducing distortion and improving frequency response.
Implementation Method 1
A test signal generator is configured to generate a test signal having a higher frequency than the target audio signal
Implementation Method 2
A current sensing circuit is configured to measure the test current flowing through the loudspeaker and to generate a current sense signal indicative of the test current
Implementation Method 3
When an electrical signal is applied to the voice coil, the coil generates a magnetic field that causes the voice coil and its attached diaphragm to move
Implementation Method 4
the effect of the magnetic field of the magnet on the coil is not constant as the position of the coil changes inside the magnet
Implementation Method 5
A feedback circuit configured to generate the feedback signal responsive to the current sense signal
Data Source
AI summary
An audio system comprises an audio driver configured to receive a target audio signal and a feedback signal and to generate an adjusted audio signal responsive to the target audio signal and the feedback signal. A loudspeaker is configured to convert the adjusted audio signal into acoustical sound. A test signal generator is configured to generate a test signal having a higher frequency than the target audio signal. The test signal causes a test current to flow through the loudspeaker. A current sensing circuit is configured to measure the test current flowing through the loudspeaker and to generate a current sense signal indicative of the test current. A feedback circuit is configured generates the feedback signal responsive to the current sense signal.