This is the first time I've ever heard of "average" power. The thing that actually kills the tweeter is called DC. An amplifier that clips is not making any more power, that's why it's clipping. What it's clipping is the top and bottom of the waveform causing squared off waves. At the very top and bottom of the squared off wave is the amplifier's maximum amplitude. As the volume continues to turn clockwise, the longer these square waves become which means even more direct current gets fed to the tweeter not only from the high frequency side, but especially the low frequency side. Alot of people don't know that clipped low frequencies are way more damaging to a tweeter than high ones again because lower frequencies are much larger and longer than high ones which makes more damaging direct current. The reason why direct current is so bad is because of two things. One, crossover components such as capacitors and inductors have no resistance to direct current since their resistance "reacts" to certain bands of frequencies which means maximum amplitude is being sent to the tweeter at the top and bottom of the waveform where it is flat from clipping. Two, there is maximum power and actually less voice coil movement which doesn't even give the tweeter the relief of cooling off simply by moving anymore. Mind you that the amplifier doesn't have to be clipping so bad to where it sounds like absolute trash for damage to take place. When speakers are driven to high volume levels they are often times being driven just under their peak performance. The added DC current at high volume levels can cause tweeter damage when the highs start to hiss and the bass gets muddy even just a little bit. This is why it's better to have more power than the speakers can initially handle because a little amplifier clipping at high volume levels will do more damage than a speaker periodically being over driven. However the sounds of being over driven are not nearly as subtle as the sounds of amplifier clipping which makes clipping even more dangerous. Also small speakers that are crossed over with a subwoofer (like most are) have to be watched more carefully as clipping is not as noticeable in the higher bass frequencies around 80Hz where many people cross them over which can make clipping harder to detect due not having the more apparent muddy low bass since that band is being handled by a different speaker.
The bottom line is that you need to know the limits of your entire system and operate your system within those limits. Pay attention to audible warnings and even smells. If you see smoke or completely lose sound from a driver in one of your cabinets it is too late. Ask me how I know lol.
Edited by Mr. Audio - 9/13/13 at 12:53am