The transistor buffer that was shown is an emitter-follower that doesn't have any voltage gain. It has voltage across it and current through it and its heating is that voltage times that current.
If you used a current-limiting resistor in series with the LED to protect the LED from burning out, then the transistor did nothing. Connecting the LED and its series resistor at the speaker would have lighted it the same.
How did you connect other LEDs?
Didn't you use a resistor in series with the transistor's base to limit its current?
If you used a current-limiting resistor in series with the LED to protect the LED from burning out, then the transistor did nothing. Connecting the LED and its series resistor at the speaker would have lighted it the same.
How did you connect other LEDs?
Didn't you use a resistor in series with the transistor's base to limit its current?