that was really confusing to understand man. One thing that people confuse and dont understand. Most speakers are hard to OVERPOWER. Underpowering a speaker will actually do more damage to it.
I don't want to start a flame war, but that is the biggest lie in the history of car audio, and gets sooo many people to buy an amp that is more powerful than they will ever use.
Speakers can be overpowered. Things that will "kill" a speaker:
1) DC voltage (can you say "pop")
2) low frequency notes in a high frequency driver (tweeters, midrange possibly). Will throw the driver's voice coil out of the gap and ruin the speaker.
3) Sustained watts over the speaker's rating. A speaker rating (50 watts, etc) is the amount of power a speaker can handle over a sustained period of time (read continuously) before reaching thermal failure. A speaker generates heat when it is moving. Depending on the design of the speaker, it can only dissipate heat at a certain rate. If you power the speaker continually with more power than it is rated, it will not be able to keep itself cool. This will cause the voice coil to heat up too high, and in most cases will cause it to melt to the gap (happens in subs often when too much power is applied). In speakers with ferro-fluid or similiar, the fluid will be burned off, and then the voice coil will fuse.
4) CLIPPED signals (goes back to a DC voltage). This is the one that the above comment has its roots in. Here is the scenario:
You buy a low powered amp (say 20 watts x 2 RMS). You hook it up, and don't think it is powerful enough. So you go to your amp, and turn up the gain setting knob as high as it will go. You go back to your HU, and turn on the music again. Hey! It is louder! WOO!! Then a few minutes later, your speakers blow. What happened?? I know, that salesman was right... I should have bought a more powerful amp, then this would not have happened! ARRGH!! WRONG
. What happened is that you set the gain control knob to what you thought was maximum, which in reality is its minimum. That gain control knob is to match the output of your HU to the input section of the amp. So if your HU has 4 volt outputs, you set the amp gain control knob to 4 volts. This makes it so that the amp knows how much to amplify your HU's signal from at the input stage. What you have done is take your amps gain control knob and set it to like 0.1 volts. So your amp is expecting at the MOST 0.1 volts, and you gave it 4 volts. So it has taken an already strong signal, and attempted to make it stronger. As it was not designed for this, the signal leaving your amp's input stage going to the output stage is CLIPPED
. In turn, your speakers were sent a clipped signal, and the clipped signal is what killed your speakers.
The included picture is an example of a clipped signal. The yellow signal is a clipped signal. The top and bottom of the sine wave have been "clipped" off, and are now just a flat line. This happens when you are asking more of your amp than it is capable of doing. Those flat lines are in reality a DC voltage... which will kill your speakers very quickly.
So, underpowered amps do not kill speakers. Someone attempting to make an amp do more than it is capable of by misusing the gain control knob can kill speakers.
This was an abreviated version... if anyone wants to read more on this, check out www.bcae1.com
for general car audio info. For specifics on too little power:http://www.bcae1.com/2ltlpwr.htm