Tweeter  Speaker Protection 

Simplist...
Light Bulb
Eminence
Parts Express
The behavior of this bulb will vary with the impedance of your tweeter. When the bulb is at its thermal limit it will draw 2.1 amps at 25 watts, with a resistance of 6 ohms. Above that it will burn out. This bulb will limit an 8 ohm tweeter to about 32 watts RMS continuous driven from a 100 Watt amplifier at 28 Volts RMS. I use it with a 45 Watt tweeter, so the tweeter is protected, but limited in power by about 1.5 db.
 This is not noticeable, and is better than burning your tweeter voice coil. On peaks, the tweeter may run much higher wattage,
but should survive if you do not run it continuously too loud.
Use bulbs in parallel for higher wattage tweeters and horn drivers.