Loudspeaker Excursion Control via FIR Filter
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Solution Overview
Problem
Loudspeakers in devices like smartphones face challenges in preventing damage due to excessive excursion and voice coil temperature, as existing technologies lack effective methods to accurately measure and limit these parameters based on applied voltage, leading to potential damage from resonant frequencies and thermal issues.
Innovation Solution
A system and method that measure excursion and voice coil temperature, using specific formulas and algorithms to generate a FIR filter, which processes the input signal to limit excursion and prevent damage, allowing for louder output without exceeding voice coil limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage limits are applied to prevent damage, then loudspeaker reliability is improved, but output volume is reduced due to guard bands for tolerances
Solution Approach 1:
The system implements feedback by measuring the actual excursion and temperature of the loudspeaker diaphragm using sensors, then using this measured information to dynamically adjust the voltage applied to the voice coil. This closed-loop control allows the system to operate closer to the true limits of the loudspeaker without exceeding damage thresholds, thereby increasing output volume while maintaining reliability.
Solution Approach 2:
The invention replaces the conventional mechanical/electrical protection approach (voltage limiting based on manufacturer specifications) with a sensor-based measurement and control system. By using optical or capacitive sensors to directly measure diaphragm position and temperature sensors to monitor voice coil temperature, the system substitutes guesswork-based voltage limits with precise real-time measurements, enabling higher safe output levels.
2Reliability
If guard bands are built in for tolerances, then loudspeaker protection is improved, but manufacturing precision requirements are reduced
Solution Approach 1:
The system enables the loudspeaker to self-monitor and self-protect by incorporating sensors that directly measure its own operational parameters (diaphragm excursion, voice coil temperature). The control system uses this self-generated data to adjust operating conditions in real-time, making the protection mechanism independent of manufacturing tolerances for sensitivity, acoustic implementation, and ambient temperature variations.
Solution Approach 2:
The invention changes the approach from using fixed voltage limits based on manufacturer specifications to dynamically adjusting operating parameters based on real-time measurements. By continuously monitoring actual excursion and temperature and adjusting the applied voltage accordingly, the system adapts to variations in manufacturing tolerances and environmental conditions, providing robust protection without requiring tight manufacturing precision.
3Reliability
If excursion measurement and control is implemented, then loudspeaker damage prevention is improved, but device complexity is increased
Solution Approach 1:
The system introduces an intermediary measurement layer between the voice coil and diaphragm using optical or capacitive sensors that non-contactually measure diaphragm position. This intermediary measurement system provides direct feedback on actual excursion without requiring complex internal modifications to the loudspeaker structure, enabling precise control while keeping the added complexity manageable through the use of established sensor technologies.
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 solution enables louder sound output while ensuring the loudspeaker operates within safe excursion and temperature limits, preventing damage by accurately measuring and managing excursion and temperature through real-time processing and filtering.
Implementation Method 1
a voice coil, coupled to a diaphragm of the loudspeaker... determine a Fourier space excursion-from-voltage transfer function... whose form is constrained by parameters H IV (ω), Bl, R vc , and L vc
Implementation Method 2
determine a Fourier space excursion-from-voltage transfer function... whose form is constrained by parameters H IV (ω), Bl, R vc , and L vc where... R vc comprises a resistance of the voice coil
Data Source
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AI summary
A method, system and apparatus for loudspeaker excursion domain processing and thermal limiting are provided. At a device comprising: a processor; a loudspeaker and voice coil, device(s) for determining loudspeaker voltage and current; a volume device; and a memory storing a Bl product for the loudspeaker, a Fourier space excursion-from-voltage transfer function HXV(ω) is determined. An acoustic response of the loudspeaker below a dovetail frequency, is determined, relative to a respective acoustic response at the dovetail frequency, using at least a second time derivative of the transfer function HXV(ω). An equalization is determined using the acoustic response, comprising gains that, when applied to the acoustic response, will adjust the acoustic response to the respective acoustic response at the respective acoustic response at the dovetail frequency. Filter coefficients are determined corresponding to the equalization, which are used in a filter applied to a loudspeaker input signal.