Hi,

The issue with an amp being ruined by driving too a
powerful speaker has been nagging me some time. How
could it get ruined? The ohms are the same 8 ohms so the
same power will be drawn through the speaker whether it
has a low power rating or a high power rating. Right??
WRONG!! I also could not understand that concept until
someone partly explained it too me.

Here is the best explanation which I can give:
A speaker designed for more power has to push more air,
the cone must be stronger. The coils are definitely
heavier. All this makes for much more mass. All this
mass has too be vibrated back and forth at incredible
speed (although you can't see it move much at higher
frequencies.) In order for the cone and coil to vibrate,
its inertia has too be overcome. Now, let’s say you are
putting in 300 watts to a 300 watt rated speaker, the
moving mass is RELATIVELY small and takes a certain
percentage of the input power too overcome its inertia.
The rest of the power is given out as sound energy into
the surrounding air. So lets say that our lightweight
300 Watt coil is consuming 50 Watts and the remaining
250 are being put out as sound. If you take the same
scenario but with a speaker rated at 1000 watt, say 150
watts will be consumed by vibrating the speaker and only
150 watts will be put out as sound. The result is of
course a much lower sound level. Ahhh, so Mr. DJ goes
and cranks up the amp to get the proper sound volume.
Guess what, the amp is now putting out say, 500 watts.
That's it: to get the same audio volume into the air,
the higher power rated speaker must draw more power from
the amp WITHOUT YOU REALIZING IT.

I am not a sound engineer, but I believe that the above
is true. It just makes so much sense. What do others think?