Driver Power Handling Limits

Depends how you blow it up.... 🤣

A very short term excess voltage can turn a driver into a missile.

Long term excess heating may eventually burn out a coil, without the need for eye protection. Many a tweeter with first order high pass filters has suffered an untimely death this way.

Closer to your question, thermal damage as well as thermal compression are real effects which must be taken into account when specifying driver limitations. The thermal management of a coil is something even more important to professional driver manufacturers. Thermal compression can happen very quickly in a consumer grade tweeter for instance, within milliseconds. It won't necessarily be damaging but the output will suffer.

The argument for thermal compression is at least one reason given by many fans of high efficiency compression tweeters. Much less power is needed, therefore much less heating and greater dynamic range without compression.

Yes, heatsinks and a ported magnet can help. Here is a much better article than I can write on the subject.
 
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I think more woofers are rated based on thermal considerations. Mechanical effects are heavily influenced by the enclosure, and the manufacturer doesn't typically specify a precise enclosure to be used.

Discussion of some cooling methods here:

 
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Thats a different question. A fan might help, but the problem is not the outer magnet structure so much as between the voice coil and magnet. The heat gets generated deep inside the magnet ring.

Also keep anything magnetic away
 
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Eminence locate a heatsink in the dust cap position of their Kilomax Pro-18A driver.

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Thats a different question. A fan might help, but the problem is not the outer magnet structure so much as between the voice coil and magnet. The heat gets generated deep inside the magnet ring.

Also keep anything magnetic away

Ridiculous. A fan makes noise and requires a power supply. The magnet, by its nature, dissipates heat. Heat sinks are generally aluminium and not magnetic.
 
The centre pole gets hotter than the rear plate/magnet assembly, so it is from the centre pole that we require to remove heat.

Eminence talks of a "cooling plug" being pressed into the centre pole in order to conduct the heat out and transfer it to a heat sink.
 
Here you can see a copper voice coil wound inside and outside the former.
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That heat it creates wicks into the surrounding motor (metal plates and magnet). Adding cooling fins to the entire outside of the motor may help reduce temperatures during sustained heavy use like would be seen at a concert. An example can be seen with this JBL driver.
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However, for home use, it’s pretty much worthless. We don’t feed our drivers “space heater” levels of power over a sustained period. If we did, not only would heat be a concern, distortion would be as well.

Edit: To answer your question, heat sinks would provide little thermal failure protection in a home environment. They’re made to reduce the motor temps after an extended (hours) period of time. In a home environment, things blow due to ham fisted use of the volume knob and/or carelessness and typically happen in short order (loud scene of a movie with the volume too loud, for example)
 
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The power handling depends on the amount of heat that the unit can take without damage, as the excursion/mechanical limits and are seldom reached in a properly designed home / studio product and environment.

The heat dissipation limits depend on the heatsinking material, as aluminium (though softens / melts earlier) is several times conductive when compared to steel. Forced air cooling using vents (JBL) are also said to be effective in removing heat. The kapton used in voice coils is temperature resistant and so is copper. Industrial adhesives can withstand 300*C with no problems.

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thrcn.html

However the loss of magnetism with temperature depends on the kind of magnet used (neodymium vs ferrite). The neo magnets start weakening before reaching 100*C even though the Curie temperatures for both neo and ferrite are high, possibly resulting in the BL product becoming a strong function of temperature. Nevertheless, a reduction in BL product only affects performance and does not damage the unit.
 
Is a typical woofer's power handling limit mechanical or thermal?
If the limit is thermal would a heatsink help? (Particularly in ported enclosures).
Only my uneducated opinion. Just on its own, the driver is going to be pretty silent and happy. It requires electrical input to do something and a box to give it an environment to move in correctly. These two will take it to its thermal and mech limits. Maybe just use lower voice coil resistance drivers to keep things cooler, e.g. 2R and 1R drivers?
 
Is a typical woofer's power handling limit mechanical or thermal?
If the limit is thermal would a heatsink help? (Particularly in ported enclosures).

Power handling is a thermal limit, established via a standard test that is something like sending broad band (white/pink) noise at some power level through the driver for a pre-determined length of time. The driver is rated to not destroy itself from this sort of power input.

But as others have mentioned, drivers have built in cooling mechanisms and for larger drivers these are based on air flow in and around the voice coil. There is more air flow when there is more excursion. If you apply Pe power at a frequency band that does not cause the cone to move it will suffer more compared to that same power applied at low frequency that causes the cone to move and more air to flow thru and cool the voice coil.

You cannot connect conductive cooling (eg a heatsink) directly to the voice coil, so air flow is probably the best way to cool. At the same time all the other parts nearby also heat up, and these can be cooled by some heat sinking. These include the frame and rear of motor, and even the pole piece (see Eminence Kilomax or drivers by VOLT). These metal parts are often designed to carry heat away in pro drivers. For home audio this is not really as much of an issue.

Also, getting cool air in and around the hot parts can be important. Mounting a driver with the motor and basket outside of the cabinet can help in this regard, but it's not clean looking or done professionally.

Despite what you might imagine, there is little air exchange from inside to outside of a ported/vented enclosure. At resonance where air flow is high there is mostly a slug of the same air sloshing back and forth in the port tube and near each end. There is not all that much fresh air mixing into it.
 
I did a 3 mm drillinghole from behind, in the center of the coils gap. (when investigating a problemdriver)
Maby with 2 hole¨s (one low and one high), you can get small convection movements inside the gap.

Also test if 2 thin copper-pipes mounted in the holes, and leads out of the box (easy to get airtight), make convection stronger.
Otherwise force air carefully through.

Just a theory!
 

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For sound quality, there's a balance. You obviously want to avoid approaching driver thermal limits, or even significantly elevated temps longer term within limits, but the cost is sometimes too much. For instance, a 4 layer 4" coil is probably way more heat than anyone will use in a home woofer in a decent sized enclosure (not a box-minimized sub). The effective thermal advantage of that coil vs. a 2 layer, when considering diminishing returns, is traded against higher Mms and higher Le as well as more complex tradeoffs. Heatsinks can help, Pi Speakers has a cooling plug/plate solution that seems to allow for quite a bit of enhanced power handling, but very short term, coil thermal mass vs. SPL is more the tradeoff, again, at the expense of Mms and Le and other derivative or 2nd order effects. So, you want to design for plenty of capacity to avoid short term limiting, but not so much that you undermine driver performance outside of thermals.

In horns you have special cases- where driver excursion is limited and that inhibits convective cooling, but the power input is lower for a given SPL, so for a given SPL, you're going to still generally manage much better thermal performance than a direct radiator of equivalent size/coil size. That's not really the tradeoff though- I'd be interested to see a study on a 4x12 array and voicecoil temps, short and long term, vs. a single 12" on an "Equivalent" horn. I suspect the tradeoffs would be about as clear as mud with frequency and SPL dependent advantages. I'd guess high sustained SPL in the midbass (so meaningful excursion) favors the array, with greater motion cooling and much more coil, but short term high crest factor peaks that advantage would dissipate (the peak input per-coil being the dominant factor) and you'd see efficiency become the dominant factor.

Hopefully I don't have to edit this but I always seem to miss or mis-state something.