Loudspeaker Protection via Predicted Excursion Gain Control
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Solution Overview
Problem
Existing loudspeaker protection systems face challenges in preventing mechanical damage due to excessive diaphragm excursion, particularly in portable devices where robust speakers are not economically viable, and existing solutions introduce unacceptable delays in applications like telephony.
Innovation Solution
A loudspeaker protection system that includes an input node for digital audio signals, a delay block, a gain block, an excursion predictor, and a gain controller, which determines gain settings based on predicted excursion and a loudspeaker impulse response model to limit excursion without requiring a delay that exceeds the impulse response settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a delay block is used to apply reduced gain early enough in the signal path, then speaker excursion is limited effectively, but signal delay increases causing problems in telephony applications
Solution Approach 1:
The system calculates and stores gain values in advance for all possible input signal combinations before they are needed. When an input signal is received, the pre-calculated gain value is retrieved and applied immediately without requiring a long delay period, thus providing preliminary protection action with minimal latency
Solution Approach 2:
The lookup table is pre-computed based on the speaker's impulse response model and excursion limits, storing the optimal gain reduction values that would be needed for various input conditions. This preliminary computation eliminates the need for real-time complex calculations and long delay periods during actual operation
2Reliability
If robust loudspeakers are used to handle maximum power levels, then mechanical damage is prevented, but device size and weight increase making it uneconomical for portable devices
Solution Approach 1:
The patent replaces the mechanical solution of using oversized robust speakers with an electronic control system that dynamically adjusts the drive signal amplitude. The excursion limiter uses digital signal processing to predict and limit speaker displacement, substituting mechanical robustness with electronic control to achieve the same protection goal with lighter components
Solution Approach 2:
The system uses a feedback mechanism where the input signal is processed through an impulse response model to predict the resulting speaker excursion. Based on this prediction, the system automatically adjusts the gain to keep excursion within safe limits, creating a closed-loop control system that protects the speaker without requiring oversized design margins
Data Source
AI summary
This application relates to methods and apparatus for loudspeaker protection. A loudspeaker protection system receives a digital audio signal comprising a plurality of samples at an input node. A delay block delays the digital audio signal and a gain block applies a controlled gain to the delayed digital audio signal. An excursion predictor is configured to receive a version of the audio signal from the signal path upstream of the delay block and determine a predicted excursion for a loudspeaker based on the audio signal. A gain controller controls a gain setting of the gain block in response to the predicted excursion and a first loudspeaker impulse response model and a predetermined excursion limit. The gain controller is configured to determine at least one gain setting {ga gi} to be applied to a set of samples {Va . . . Vi} of the audio signal delayed by the delay block where the set of samples of the audio signal corresponds to a time-span which is less than an impulse response settling time of the loudspeaker.