Q:

Read Values from a Speaker

I am using Arduino UNO and did a project to sync LED to audio. I am not sure how to read a value from a speaker.
I connected a LED to Pin 9 (PWN) with 220ohms and ground. I connected A0 pin to a speaker pin and ground pin the other pin on speaker. I used the Smoothing example of arduino input and modified the code a bit to output to LED.  The speaker I used was with an old Phillips Music System and had only two pins. I played the music and led synced perfectly and everything worked fine. The project was a success.
Today I wanted to try to connect to a home theater (5.1 Sony HT-IV300 Model). This speakers also have same 2 pins. So I did everything same. A0 to Speaker pin 1 and Ground to Speaker pin 2. But suddenly the Music System went to power protect mode and A0 is stuck at ~1000 (975 - 977). I connected the arduino again with the Phillips Music System (Same setup) but A0 is always gives ~1000 value. Connecting to A1 and changing the code works perfectly fine!
Where did I go wrong? I cannot understand, what happened to A0 pin? What is the correct way to read the speaker values?
Thank You.
Abhi 

A:

How could it be destroyed? Voltage is merely 0.15 volts (according to
  multimeter)

If it were 0.15 volts and the speaker was an 8 ohm speaker, the power output to the speaker would be 0.15*0.15/8 = 0.028 watts. Does this seem likely or does it seem more likely that the multimeter isn't giving you the full picture?
If in fact you were driving 1 watt into the speaker, the RMS voltage would be 2.828 volts with a peak voltage of  that is significantly higher maybe 4 to 10 volts for music type signals.
This level of voltage and the level of current that the amplifier output is capable of providing will certainly damage an ADC input on a chip. Next time use a 10k resistor in series and maybe also a coupling capacitor.

