How do I determine if a speaker is "blown" or if its a signal issue?

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Long story short: I upgraded a lot. I had 6.5" Coustic separates in the front and 6x9 Eclipse 3-ways in the back running off a factory head unit for MANY years. I think I installed those in 99 or 00. I recently built some nice enclosures for 10" subs and drove them with 900wrms so I upgraded to 75wrms x 4 to drive the existing speakers. (actually two 75x2 amps)

The Coustics in the front didn't last long. I lost the mid on the right channel and the tweeter on the left, but its not a big loss. I never really liked them anyway.

The 6x9s sound like the mids might be blown. Certain frequencies (usually in vocals) are fuzzy.

It sounds like a blown speaker, but I have to second guess because I screwed up during installation. While I was setting gains and crossovers, I was laying on the factory speaker wires and directly shorting the head unit's amp. By the time I realized it, the wires were pretty warm. I assume that would fry the amp but not the preamp outs (which is what is driving the amp) but could it have done more damage in the HU?

Am I over thinking it and I should just get new 6x9s, or is it possible that I did damage to the HU and that is where the problem is? How do I test it without throwing parts at it?
 
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The ICs used in your head unit have short circuit protection so no worries there.

You probably damaged the speaker with too large cone excursion. You could check the coil for shorts by measuring the resistance across the voice coil connections, it should be close to the driver's 'Re' spec. You can listen for rubbing or other strange sounds while you push the cone in and out with your fingers. It should be silent and not rub at all. Tap the cone, frame, motor with wood or plastic and listen for broken, rattling type sounds. Do the same to the hole where the driver is installed, the high SPL could have loosened up something in the door, etc.
 
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