SSZTDE7 October   2026 TAS2573 , TAS2781

 

  1.   1
  2. 1 Introduction
  3. 2 The physics of microspeaker vulnerability
  4. 3 Traditional versus smart approaches to audio design
  5. 4 Integrated IV-sense circuitry
  6. 5 The temperature protection algorithm
  7. 6 Thermal modeling and control
  8. 7 The excursion protection algorithm
  9. 8 Look-ahead limiter
  10. 9 Integrating the audio tuning chain
  11. 10Conclusion
  12. 11About the authors
  13. 12Additional resources
  14. 13Trademarks

6 Thermal modeling and control

Because the RE measurement only arrives periodically, the algorithm needs a way to know the voice coil’s temperature continuously, in the gaps between measurements. The solution is a predictive thermal model – a multistage resistor-capacitor thermal network (see Figure 4). This model simulates heat transfer from the voice coil to the speaker magnet structure, and finally to the device’s chassis and ambient air, and it runs at the full control-loop rate. Each time a new, IV-sense-based RE reading arrives, re-anchors the model, and corrects any drift accumulated since the last checkpoint.


Loudspeaker predictive thermal model

Figure 4 Loudspeaker predictive thermal model

By tracking heat dissipation paths in this way, the algorithm can predict how fast the temperature will rise during an upcoming audio peak and how quickly it will cool down during a pause. This estimate feeds a power controller that enforces the safe operating limit of the audio signal continuously and without interruption. As the estimated voice coil temperature approaches the Tmaxof the loudspeaker, the controller reduces the permissible limit to protect the loudspeaker from overheating. When the loudspeaker cools down during soft audio segments, the controller will allow higher-power delivery to the loudspeaker.

The thermal protection algorithm controls the audio signal based on the power limit predicted by the thermal controller, applying a smooth, broadband gain reduction that lowers the overall root-mean-square (RMS) power delivered to the speaker so that the voice coil can cool down without abrupt, audible drops in volume. This gain reduction uses slow attack and release times; because human hearing is less sensitive to gradual changes in overall volume, the attenuation blends seamlessly into the background, preserving the perceived dynamics of the audio. See Figure 5.


Closed-loop temperature protection

Figure 5 Closed-loop temperature protection

In Figure 6, the blue curve represents the smart amplifier’s estimated temperature, while the red line indicates the Tmax limit. The amplifier dynamically modulates the audio to ensure that the speaker is always within reliable temperature limits (leaving some headroom for IV-sensing errors).


Smart amplifier temperature estimation vs the Tmax limit

Figure 6 Smart amplifier temperature estimation vs the Tmax limit