Some (not all) of you people have no idea what you are talking about and should understand how audio systems work before attempting to give advise. Some of the statements given are false. "running DC power to a voice coil". A speaker cone operates off of alternating current. Don't believe me? Hook up the speaker terminals to a battery and watch the cone move in only 1 direction. Next hook the terminals up to an AC wall plug(fun to do but the speaker won't last long)and you will get a 60HZ tone--50HZ overseas.
The gain control thing "just turn up/down the gain on your amplifier". The sole purpose of the gain control is to match the input level of the amplifier to the head unit's voltage pre-output. The gain control is not a volume knob. If you have a higher end head unit with a full 4 volt pre-out, then you would set the gain on the amp to 4 volts(which would mean all the way down, or close to it depending on the manufacturer). "But then it won't be loud enough" Get a bigger amp! That's what those little numbers on the gain control are there for.
As far as "blowing speakers" are concerned, someone did get it right by stating "there are only 2 ways to blow a speaker". Mechanical failure, possible yes, likely no. Most frequently the voice coil's tiny wire burns because it's thermal limit has been exceeded.