My speaker burned out because your power amplifier is emitting DC.
Parsing
1) The power amplifier does produce DC, and the DC protection circuit of the power amplifier fails.
2) If the DC protection circuit of the power amplifier is tested to be normal, then it is not that the power amplifier has produced the DC speakers. The main reasons are:
a. The power amplifier does not have a voltage limit protection circuit, and the input signal is too large, which causes the output signal to produce clipping (square wave) and the output super distortion power burns the speaker;
b. The power amplifier has a voltage limit protection circuit, and the input signal is too large to exceed the control range of the voltage limit protection circuit, causing the output signal to produce clipping (square wave) and the output super distortion power to burn the speaker.
3) For some power amplifier products, if the protection light (PROT) can light up normally, even after a failure, it can be judged that the DC protection circuit of the power amplifier is normal, and the protection light is on but the protection function fails. It is very rare.
4) The speaker wiring is reversed (sometimes).