Voice Coil Current Reversal in Multi-Gap Speakers for Bass Linearity
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Solution Overview
Problem
Existing speakers, such as those described in JP 2000-197189 A and JP 5-227593 A, face issues with linearity of driving force when reproducing bass tones, leading to distortion due to opposing magnetic flux directions in different magnetic gaps, which is unsuitable for subwoofers requiring large-area vibration plates with large amplitudes.
Innovation Solution
A speaker design with a magnetic circuit section featuring multiple magnetic gaps, including a main and sub-magnetic gaps with opposite magnetic flux directions, combined with a vibration controller that reverses or attenuates current direction or magnitude to maintain linearity of driving force, using a detector to monitor voice coil position and adjust current accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If two magnets are used to concentrate magnetic flux in the central magnetic gap, then the driving force for large-area vibration plates is improved, but the linearity of driving force deteriorates when voice coil enters sub-magnetic gaps causing distortion
Solution Approach 1:
The patent dynamically controls the current direction to the voice coil based on its position. When the voice coil enters the sub-magnetic gap, the controller reverses the current direction to counteract the opposing magnetic flux, thereby maintaining linearity of driving force throughout the full range of motion while preserving the concentrated flux benefit in the main magnetic gap
Solution Approach 2:
The patent changes the electrical parameter (current direction) in response to positional changes of the voice coil. By detecting when the voice coil enters the sub-magnetic gap and reversing current direction, the system adapts the driving parameters to maintain consistent force linearity across different operational states
2Speed
If large amplitude vibration is used for bass reproduction, then the sound pressure output is improved, but distortion occurs due to braking force from opposing magnetic flux in sub-magnetic gaps
Solution Approach 1:
The patent applies preliminary anti-action by reversing the current direction before or when the voice coil enters the sub-magnetic gap. This preemptive measure counteracts the opposing magnetic flux that would otherwise create braking force and distortion, enabling sustained large-amplitude vibration for bass reproduction without quality degradation
3Length of moving object
If voice coil enters sub-magnetic gap during large amplitude operation, then the driving range is extended, but braking force acts on voice coil impairing linearity
Solution Approach 1:
The system dynamically adjusts current direction based on voice coil position. When the detector identifies that the voice coil has entered the sub-magnetic gap, the controller reverses current direction to eliminate braking force, thereby maintaining driving force linearity throughout the extended travel range
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
Ensures linearity of driving force and reduces distortion in bass reproduction by effectively managing magnetic flux interactions, allowing large-area vibration plates to operate with minimal braking forces, thus improving sound quality.
Implementation Method 1
a magnetic flux is generated by a magnetic circuit section and crosses the voice coil
Data Source
AI summary
A magnetic circuit section having a main magnetic gap and sub-magnetic gaps is used. A vibrator is vibrated by an electromagnetic force generated by a voice current, which flows through a voice coil and a magnetic flux crossing the main magnetic gap. When the voice coil approaches or enters a sub-magnetic gap, the voice current which flows through the voice coil is reversed, temporarily cut-off or attenuated.