Speaker Back-EMF Feedback for Nonlinear Distortion Control
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Solution Overview
Problem
Speakers face non-linear parameter changes due to cone movement, leading to distortion, which existing solutions fail to effectively address, especially in small speakers where sound quality is compromised by non-linearities and excursion limitations.
Innovation Solution
The system employs a BEMF extractor to measure sense voltage and current at the speaker, calculating the voltage drop across the speaker impedance to determine BEMF, which is then used in a feedback loop to adjust the audio signal and compensate for non-linearities, thereby reducing distortion and increasing excursion while maintaining sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing solutions are used to address speaker non-linearities, then distortion is reduced, but they fail to effectively address non-linearities in small speakers due to excursion limitations
Solution Approach 1:
The patent implements a feedback mechanism using back electromotive force (BEMF) sensing to detect speaker cone movement in real-time. The BEMF extractor measures the voltage generated by the moving coil in the magnetic field, which is directly proportional to cone velocity. This feedback signal is then used to adjust the audio signal, enabling dynamic compensation for non-linearities and excursion limitations specific to small speakers, thereby resolving the contradiction between general distortion reduction and effectiveness in small speaker applications
2Manufacturing precision
If adaptation loops are used to compensate for non-linearities, then sound quality is improved, but lag is introduced reducing bandwidth
Solution Approach 1:
The patent applies preliminary action by using the BEMF signal, which naturally leads the cone position signal by 90 degrees (BEMF is proportional to velocity, which is the derivative of position). This phase relationship allows the feedback system to anticipate and compensate for non-linearities before they fully manifest, reducing the need for heavy filtering and adaptation that would introduce lag. The system proactively adjusts for expected non-linear behavior based on the instantaneous BEMF measurement, maintaining both sound quality and bandwidth
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 approach effectively reduces non-linearities and increases speaker excursion, improving sound quality by directly tracking cone movement in real-time, avoiding the lag of adaptation loops and maintaining acceptable bandwidth, particularly beneficial for small speakers in constrained applications.
Implementation Method 1
Current flowing through the coil causes a magnetic field, and the coil moves rapidly back and forth due to the interaction of the magnetic field and the permanent magnet
Implementation Method 2
BEMF extractor is configured to extract a sense voltage and a sense current at the speaker... subtract the voltage drop from the sense voltage to determine a BEMF
Data Source
AI summary
A system includes a feedforward path coupled to a signal input. The system also includes a speaker coupled to the feedforward path. The system includes a back electromotive force (BEMF) extractor coupled to the speaker, where the BEMF extractor has a first input, a second input, and an output. The BEMF extractor includes a first summing point coupled to the first input. The BEMF extractor includes a resistor amplifier coupled to the second input and the first summing point. The BEMF extractor includes a high pass filter coupled to the second input and to an inductor amplifier. The BEMF extractor also includes a low pass filter coupled to the first summing point. The BEMF extractor includes a second summing point coupled to the low pass filter, the inductor amplifier, and the output.