How do speakers get blown? Why do they sound distorted?

How do speakers get blown or why do they sound distorted? Speakers can sound "distorted" or be "blown" in a few different ways. Distortion is usually not damaging to the speaker, however there is a difference between a distorted sounding speaker and over-powering speaker.

Good Voice Coil

Over-Powering Low Frequency Speakers (subwoofers)
Failures in subwoofers are caused either by ELECTRICAL and/or MECHANICAL power handling issues. Electrical failure occurs when applying to much power to the subwoofer(s) and causes the voice coil(s) to "burn". This can be the result of incorrect gain settings or improperly wired subwoofers, which can cause a low impedance load on the amplifier. For proper subwoofer wiring methods, please refer to our Woofer WiringWizard. Mechanical failure occurs when the speaker physically rips and/or tears. Improper enclosure size is the primary cause of mechanical failure. As a general rule, always try to stay within +/- 25% of the manufacturer's recommended enclosure volume (Vb) to ensure best performance. If the subwoofer enclosure is too large, the mechanical suspension of the subwoofer will be compromised, causing the spider or surround to physically tear and/or possibly separate from the speaker's frame. Using an enclosure that is smaller than the one recommended by the manufacturer will usually not cause any adverse power handling effects and is more likely a safe bet. A secondary cause of subwoofer failure is an improperly vented enclosure. Improper tuning can cause the speaker's mechanical power handling to be compromised below that of the "tuned" enclosure frequency. Checking the port diameter (Pd) and length (Pl) in relation to the internal volume (Vb) of the enclosure is recommended to match that of the manufacturer's recommendations.

Over-Powering High Frequency Speakers (midrange + tweeters)
Failures in tweeters, midrange and midbass speakers are caused by ELECTRICAL and/or MECHANICAL power handling issues. Most failures occur from ELECTRICAL failure caused by applying too much power to the speaker's voice coil. Constant over-powering results in "burned" voice coils. The only fix for this is to reduce the amplifier gain controls and/or treble/bass boost controls or not to drive your audio system so hard. Distortion is not damaging to a speaker. However, if you hear distortion long before reaching peak system volumes, it's just a good idea to readjust the amplifier or signal processor gain controls and/or readjust the equalizer settings to maximize your sound quality. MECHANICAL failures occur by using the wrong crossover point for the speaker. Usually, too low of frequency applied to a small suspension type driver (tweeter/midrange) can physically cause the speaker surround to delaminate. The only solution for this type of failure is to follow the manufacture's guidelines for proper crossover frequency and crossover slope.

Burned Voice Coil

The "Dirty" Truth About Distortion
Contrary to popular belief, distortion does not cause speaker damage. Distortion is merely the audible detection of signal "clipping". Clipping is when an audio component can no longer provide enough power supply voltage to "cleanly" amplify the audio signal. Clipping can occur at any point in the signal chain (souce unit, signal processor, amplifier, etc.) The popular belief is that if an amplifier "clips" it will send D.C. current to the speaker's voice coil and "burn" it. THIS IS NOT TRUE. It would surprise you to realize nearly every car audio system's amplifier "clips" when listening to music at moderate -to- loud levels. Electrically overpowering a speaker is caused by continually playing the audio system loud, resulting in applying more power to the speaker than it's "rated" specifications. This is what causes speaker voice coils to "burn". However, for "sound quality" reasons it is important to match the source unit, signal processor and amplifier gain settings to optimize levels and minimize noise floor (system hiss.) For tips on equalizer level settings, please see Answer ID #69 - How do I adjust my equalizer?.