"Jay" wrote in message
...
Sorry, that was a bit uninformative..
They weigh about 2 or 3 pounds/piece. They didn't come with back braces,
and they would probably mount ok... my concern is the shock of slamming
over wakes over time, cracking the perimeter...

Get yourself a piece of 3/4" birch ply. Cut a square for each speaker, about
2" bigger than the speaker. Cut your holes in the fiberglass. Make them
perfect. Put the birch ply behind the holes you've made, trace the holes
onto the plywood, and cut holes in that, too. Actually, do that ***BEFORE***
you've cut it into squares. The big piece of ply will be easier to clamp to
a work surface than the smaller squares. Mount the speakers with the wooden
squares as bracing from behind.

One thing you didn't mention: What will be the enclosure BEHIND the
speakers? For any speaker, there's a very small range of correct enclosure
size. Get far from that range and the speaker becomes all but useless in
terms of bass response. Trying to get decent bass by dicking around with
tone controls will just overdrive your radio or amplifier, and blow up your
speakers in short order. Hint: In even the quietest cars, you need about 75
***CLEAN*** watts per channel to overcome road noise. If you intend to run
this stereo in a boat while the engine's running, you need about twice that
much power. Otherwise, you'd better be a big fan of distortion and blown
speakers.