Car Stereos/1999 sunfire gt stereo
Hello Brian, just curious, although the damage seems to have been done. If someone hooked a large subwoofer with a Sony 2500 amp to the factory stereo, would that blow the factory speakers... I have a very sad daughter since this is her first car, she loves it and now all the speakers are blown. She didn't request this, it s done without her permission.
Adding an amplifier and subwoofer to a factory audio system should not have any effect on the factory speakers--in fact, if it's done right, it can help preserve the speakers, because you can cut some of the bass out of the front and rear speakers and let the subwoofer play it instead.
The power of the amplifier all goes toward driving the subwoofer. The speakers remain connected to the amplifier built into the factory head unit, so they'll still get the same level of power that they got all along.
Now, it's certainly possible that someone who just installed a new subwoofer and amplifier might find a bass-heavy song and turn the volume up to see how loud he could make the subwoofer play, which could in turn damage the stock speakers. If that happened, though, you couldn't really blame it on the subwoofer--if the radio is turned up too loud, it can damage the speakers whether there's a subwoofer connected or not.
Another possibility is that whoever installed the amplifier didn't connect it correctly to the factory wiring. If someone tried to tap into the factory speaker wires to make the amplifier work, then it could cause an overload on the head unit's built-in amplifier and result in a distorted sound that might resemble blown speakers. However, in that case the problem should have gone away when you disconnected the amplifier and returned the factory wires to their original condition.
I should mention that if I saw a '99 Sunfire (or Grand Am) with the original speakers, I'd consider it more likely than not that the speakers would sound "blown" or rattle. It's a very, very common issue in these vehicles, and it doesn't necessarily mean that someone's been abusing the audio system.
That vehicle uses a 4x6" speaker in the front doors, and a 6x9" speaker on the rear deck. Both sizes should be easily available at any store that sells car audio equipment. Here's a guide to the vehicle that will help if you want to try installing new speakers on your own: http://www.scosche.com/media/guides/pc381.pdf
Hope this helps!
P.S. I saw that you posted the same question earlier about a Grand Am rather than a Sunfire. I'll assume that since this question came later, that the Sunfire is the right vehicle, and I'll cancel the duplicate question.