When ANY amplifier goes into clipping ( severe saturation ), the peak to average ratio is severely reduced. When standing on the throttle, the peak to average ratio is 1/1. That's because the peak becomes the average. Needless to say, this sounds pretty horrid in terms of hi-fi use but it can be put to good use in other forms of electronics.
Since the the peak to average radio is reduced, the heating power generated by the circuit is increased by that same measure. In other words, if we had a 10 / 1 peak to average ratio and went to a 5/1 peak to average ratio ( due to compression on the recording ), the average listening level would be higher and so would the average power consumed. As a side note, i didn't pull those figures out of my hat but selected figures that somewhat represent a Classical recording vs that of a "rock" recording.
As we start to drive a system into clipping, the average power is now so high that heat is being generated within the amp. That is because it has to generate a higher average voltage and current level simultaneously whereas it was only delivering voltage and current before as it was needed on a dynamic ( peak ) basis. That same transfer of energy is taking place at the speaker. As such, the acoustic output of the speaker is not only higher, so are the thermal losses. This is because most speakers will go into compression when driven harder due to displacement limitiations within their own suspensions. The lost energy due to lack of motion / constriction in the suspension is therefore dissipated as heat in the motor structure. If the motor structure can't dissipate the heat as fast as the energy is being applied, and this level of energy is sustained for a long enough period of time, the heat literally melts the insulation off of the windings in the coil and / or engulfs the voice coil former. The typical results of such a situation are the driver opening due to a broken connection, the driver shorting out due to the lack of enamal insulation between windings or the driver binding up due to excessive thermal expansion of the voice coil / coil former. If any of these situations occurs, we would hope it was the first one i.e. the driver opening up internally. This produces a high impedance which limits the power draw from the amplifier circuit. If the driver were to short out, it would produce a low resistance to the amp, possibly doing damage to the amp from excessive current draw and / or igniting the driver as it tries to dissipate all of the power that it is consuming. The last variable in the equation i.e. the dragging or bound up driver will still dissipate energy but at the same time, creates a highly reactive load. In most cases, trying to get the driver to move / produce higher levels of sound will result in the driver opening up internally. None the less, if a driver does not move freely, i would NOT try to "break it free" by driving the tar out of it with an amp. As mentioned above, the results might not be pretty.
Other than that, it's been my experience that it is easier to blow a speaker with either too much power or improper design of a crossover network. Both result in the same thing i.e. over-excursion & displacement limited binding due to over-drive / too much power. Modern day woofers of even reasonable build quality are typically quite rugged. Due to their smaller motor structures and limited ability to displace heat, midranges and tweeters are far more susceptible to being over-powered. Just bare in mind that clipping DOES increase the average power, so in effect, clipping is just another form of overdriving the speaker / feeding it more power than it can dissipate. Sean
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