Speaker Componant Damage
Why do speakers "blow"?There are many reasons speakers "blow". The most common ones include over powering, under powering, transients, feedback, dropping and bad cables.
This is the one that gets the most attention, but is not the one that causes the most problems. You really have to exceed a speaker's rated power for an extended period of time to cause it to fail. It happens, but it doesn't cause as many failures as people think it does. If your amplifier puts out an amount of power similar to what your speakers are rated for (even if it is somewhat more), you will be fine.
Yes, you read it right - under powering can blow speakers. In fact, it is a very common cause for speakers failing. This is a little bit difficult for people to understand, however, we will attempt to present a brief explanation here. Speaker science is very complicated (very few people in the world understand it fully), so we cannot hope to give a very thorough explanation in just a few lines in this booklet.
When a speaker receives power from your amplifier it converts most of the power into sound by moving back and forth and causing the air to vibrate. However, it is not 100% efficient and some of the energy is converted into heat. The higher the power, the higher the heat. When a speaker is given a signal that is clipped, it actually receives far more continuous power than it would when it is given a clean (not distorted) signal. This is converted into more heat than the speaker was designed to handle and the coil literally burns. It can, in extreme situations, actually catch on fire (remember, the cone is made of paper)!
So, you can use a power amplifier that puts out considerably less power than the speaker is rated for, and yet, because it is being run into clipping, the speaker will blow. The harder the amplifier is clipped (the louder the distortion), the greater the chance of this happening. Tweeters are particularly sensitive to clipping because a clipped signal generally has lots of extra high harmonics (high frequencies) and tweeters are normally able to handle only small amounts of power. However, woofers can be blown due to clipping as well. It's not the under powering that causes the problem, it's the distortion that often occurs as a result of under powering that is the culprit.
This is just a fancy name to describe sudden loud sounds. One of Isaac Newton's famous laws states that a body in motion wants to stay in motion. Just like a car wants to keep going forward unless you apply the brakes (it doesn't just stop instantly when you take your foot off the gas pedal), a speaker wants to keep going forward (or backward) when it is given an amplified signal. If it goes from a low volume (or no volume) to a very loud volume (especially if this sound exceeds the power handling of the speaker), the cone wants to go farther than it was originally designed to go. In the forward motion it can extend so far that it rips, and in the backward motion it can go back so far that it either rips or hits the magnet assembly and breaks.
Common transients include turning on something that goes "pop" when the amplifier is at full volume (always turn the amplifier on last and off first), dropping a microphone when it is on, or plugging and/or unplugging a cable into/out of a P.A. component when the amplifier is on.
Feedback is the loud squeal that is often heard in a P.A. system when a microphone is pointed too close to a speaker cabinet or the volume gets too loud. A squeal lasting less than a second is generally harmless (although it can act like a transient sometimes and cause failure – see above). However, keep feeding back for very long (more than a second is often all it takes) and the tweeters and/or horns will get so hot that their coils burn and they stop working.
Most P.A. speakers can take a degree of rough handling. However, if a cabinet takes a hard enough impact, it is possible that internal parts of the speaker can shift. Speakers have heavy magnets hanging off the back of them and momentum on a hard enough drop will cause the magnet to shift. Remember, the way a speaker creates sound is by vibrating hundreds and even thousands of times per second – it doesn't take much of a shift to throw the alignment of the various parts of a speaker out enough that they will rub. When a moving part on a speaker rubs, the part receiving the friction eventually rubs through and causes the speaker to fail. Usually it is the wire in the coil that is rubbing and it eventually rubs so thin that it breaks or shorts, thereby causing the speaker to stop moving.
Besides all of the other nasty things we have discussed about using improper cables, another problem they can cause is oscillations. Oscillations can occur in a P.A. system when the ground has come off in a cable. Everything may seem to be working alright but a missing ground can cause a high frequency (high pitched) sound that is so high that you cannot hear it, but it is, nonetheless, causing the tweeter to burn out. A high quality cable is much less likely to have a bad ground connection than a lower quality one, and one blown tweeter can pay for a significant number of good cables.