Speaker Temperature Protection by Selective Frequency Scaling
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Solution Overview
Problem
Conventional temperature protection methods for speakers reduce perceived loudness significantly when the voice coil temperature exceeds a threshold, as they typically reduce the amplifier's gain across the entire input voltage signal, leading to potential speaker damage from overheating.
Innovation Solution
The system filters the input signal into component signals, where the perceived loudness is more sensitive to one signal than the other, and scales the less sensitive signal based on estimated speaker temperature to maintain output while reducing power to the speaker, thereby protecting it from overheating without significantly impairing perceived loudness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the amplifier's gain is reduced across the entire input voltage signal when voice coil temperature exceeds a threshold, then the speaker is protected from overheating, but the perceived loudness to a human is significantly reduced
Solution Approach 1:
The input voltage signal is divided into multiple frequency components using a polyphase filter bank. Different frequency components are processed independently, allowing selective gain reduction only for frequencies that contribute significantly to voice coil heating while preserving frequencies that contribute to perceived loudness.
Solution Approach 2:
Different gain adjustments are applied to different frequency components based on their individual characteristics. Frequency components that contribute more to heating receive greater gain reduction, while those contributing more to perceived loudness maintain higher gain, creating a non-uniform local quality adjustment across the frequency spectrum.
2Reliability
If the amplifier's gain is reduced across the entire input voltage signal to protect the speaker, then the temperature is controlled, but the overall sound output and perceived loudness are impaired
Solution Approach 1:
The signal is segmented into frequency components that can be independently controlled. This allows the system to maintain high gain for frequency components that contribute to sound quality and perceived loudness while applying gain reduction only to components that cause excessive heating, thereby maintaining both speaker protection and sound output quality.
Solution Approach 2:
The gain parameter is changed differently for different frequency components based on temperature conditions. The system dynamically adjusts the gain parameter for each frequency component, reducing gain for heating-prone frequencies while maintaining gain for loudness-contributing frequencies, thus preserving overall productivity.
Data Source
AI summary
For protecting a speaker, an input signal is received and filtered into component signals. A sum of the component signals is approximately equal to the input signal. The component signals include at least first and second component signals. A perceived loudness to a human from the speaker is more sensitive to the first component signal than to the second component signal. A temperature of the speaker is estimated. In response to the estimated temperature, the second component signal is scaled. An output signal is output to the speaker in response to the first component signal and the scaled second component signal.