Speaker Protection!

[iancrt]

hi.

I run BMX race events, and to do this we run a PA system outside.
This is made up of a twin CD into a mixer into an Amp, all mounted in a Flightcase. The Amp is farly powerful rated at 550W RMS into 8Ohm (750W peak)
All fairly simple however on Saturday I blew two sets of speakers. Ok they werent fantastic speakers I dont even know what they were rated at. the first pair were pretty big I think 100W RMS and they were fine until we started commentating and died due to voice levels I think. (The second died at the the end of avril lavigns Skater Boi but they were even smaller speakers)
As replacements I have aquired some more speakers, these are rated at 150W RMS, 300W peak.
Obviously the amp is way too powerful, but if I dont turn the volume up too much should be fine.
Now the problem is, no-one is present monitoring the system, neither am I usually on the correct side of the speakers to hear any of the tell-tale distortion of a speaker being overloaded. On top of this, its not always me that sets up the system and starts it going so levels may not be checked correctly no matter how many warning stickers I place on the equipment.
So I need an idiot proof way to protect the speakers. Short of buying bigger speakers - which club funds cannot stretch to - various options seem to exist - fuses, thermisters, circuit breakers, car bulbs (?). I also wondered if I could add a resistor in series to increase the load and hence reduce the power.
The amplifier has a breaker which I think will protect it from any sudden loss of output load.
Any advice and suggestions would be welcome.

[Dave Boulden]

The only old trick I can recall is to wire a lightbulb of some sort in series with the speakers that should soak up extra signal. I've never tried it myself, but have been told by a touring PA guy that it's an old trick that used to be used on PAs (and might still for all I know... in fact we have festoon lamp styled fuses in our crossovers that glow when we crank up our own PA). It works kinda like a natural limiter.

You'll need someone a bit more knowledgeable on the subject than me to work out what size and power lamp you'd need to use.