I've never heard a blown speaker before but the highs and upper midrange sound great in all four infinity 6 1/2" speakers that I have but when there is any bass at all (even on semi low volumes) there seems to be a lot of vibration coming from the doors (and if you go to the trunk, from the rear deck as well, you can't hear the rears vibrating from inside the car).

I only have the Alpine's HU power going to the 4 speakers right now but it should be well within the recommended 2-50 watt RMS power. I also don't play the volume super loud.

How can I tell if it is blown or is just some heavy vibration on the doors? Would there be no sound at all if it is blown?

If it is vibration what is recommended? Different screws? Using dynamat around the speaker?

Also what would be recommended for crossing out the lows from the 6 1/2" coaxs, a separate crossover, or just capacitors put between the speakers and line?

I eventually want to get a 50x4 amp with a variable crossover system to run the four speakers, I just don't want to go through the hassle of installing it and a thicker power cord after just spending money on a new amp and HU.

Thanks!