Just to clarify several issues I am seeing about bad / odd smells with your woofers

[toaster 10+ year member]

Yes, but mechanical and thermal limits of a driver are very often 2 different power values, within a given range of frequencies. If your smelling a subwoofer burning, it's not because the cone is moving too far, it's because it's seeing to much power. While a SSF can help this by taking away some of the power as well as limiting excursion that may very well be damaging the woofer, it's not the key issue. As a matter of fact it's almost the opposite. You tune a sub at box at 45hz and run 10hz tones through it all day and NEVER smell coils burning. Unless your woofer has the stiffest suspension known to man your going to bottom it out and damage the suspension first. Simply modeling where a you need to set a SSF with a modelling program is fairly reliable unless you have your system sitting very close a wall. Worst case it gives you a good starting point as you can see how fast you run out of xmax below tuning.
I agree that with many companies recommending high tunings for their sub that a LPF is a necessity, however I dont' feel ti's why people are complaining of coil stink. That's simply too much power at any frequency and the gains need to be lowered.

You may play your subs @ 10 cycles all day without smelling the coils, but not at or near full excursion (which is what I posted earlier). Any time the coils moves past the gap, its power handling is drastically reduced. Usually, the woofer's suspension is not damaged, it is the voice coil former that gets warped whenever it travels past excursion limits.

When I worked in the industry, and customers would ask "how much power can I put on this sub?" my answer was always "as much clean power as you can afford." Because in a properly built and tuned system, a woofer is capable of handling much, much more power than it is rated for (unless you are talking about cheap flea market equipment). I have literally thrown 2 Linear Power 4.1HVs (one per coil) on an old Punch 15. Granted, this was a special application, and had a very narrow bandwidth, but you can see what I mean. Amp gains/clipping have very little to do with damaged speakers. While it is possible to overpower a speaker, 99% of the time the speaker fails from improper install/tuning.

An amp gain knob will make a speaker system get louder, quicker if it is adjusted poorly. Once it has reached full output for any given input level, it will begin clipping. Clipping due to an improperly adjusted gain shows up on a scope as square waves, which translate to the ear drum as distortion. Distortion has never killed a speaker (open the flood gates...).

There IS a type of clipping that will kill a speaker, but it is due to the electrical system not being stiff enough to supply the needed voltage to an amplifier. When that happens, the amplifier will begin throwing DC current from the output taps, and DC current WILL kill a voice coil.