It used to be that you could go to Radio Shack and buy bare speakers. In the 1980s I bought some 6"x9" speakers for my '75 Impala which cost $10 and could handle 30 watts each. They were perfectly acceptable speakers, even though they didn't have a brand name on them.
I've always preferred to buy "enough" rather than go overkill. If your amplifier kicks out a maximum of 20 watts, you don't need speakers that can handle 100 watts, no matter how cool they may be; and speakers get expensive fast.
The same goes for just about any kind of consumer audio equipment, really. When I got my first receiver, it was 60 watts per channel, and I don't think I ever turned it up much past halfway; that was more than loud enough, believe me. The new receiver I got earlier this year kicks out around 100 watts per channel but I don't even use a large fraction of that power. This receiver had the features I wanted, which is why I chose it; I don't really care about the power output as long as it's over about 50 watts per channel.
As for the Fiero, the car stereo is a Pioneer CD player. The dash speakers have never sounded very good; they're the original speakers and they've been subjected to direct sunlight and pollutants for 21 years, now. When I got them out this afternoon I saw that, yes indeed, the suspension was cracked in several places. This confirmed what my ears had already told me many times, because any time the stereo put out any bass, the sound would distort.
The speaker consists of five basic parts. There is the frame, the magnet, the coil, the cone, and the suspension.
The frame is the metal part to which everything attaches. The magnet and coil are the heart of the speaker, which work together to turn electricity into sound. But the cone is what moves the air, and without the suspension the cone will just flail around and make noise instead of sound.
Cones are usually made either of paper or plastic; there are some which are made from thin metal. The suspension is normally some kind of foam or other flexible material. The cone can be perfect but if the suspension is no good, the sound will distort and the speaker will sound like crap.
Once I was trying to explain, to a couple friends,the demise of some speakers of mine; I could not remember the word "suspension". Here's how that conversation went.
Me: The, uh, uh...
Me: Yeah. The penis. The penis rotted away, so the speaker was shot....
Well, it is possible to have speakers re-coned, but I'm not sure it's worth the money when you're talking about OEM speakers. I wanted to go to Radio Shack to buy a pair of replacement speakers, but naturally RS no longer sells them. So I went to Best Buy--every time I'm there I get bludgeoned by the bass coming from the car stereo area, but naturally they don't carry 4"x10" speakers. Finally, I decided to check Autozone...and they, at least, did have what I was looking for: 4"x10", 25 watts RMS power handling, $15 each.
Naturally these speakers did not have GM connectors on them, but I had already figured out the solution to that problem: rather than cut my wiring harness, I simply removed the connectors from the OEM speakers and made adapters using some female spade lug connectors and a bit of speaker wire. With them patched in, the new speakers sounded great...but they would not fit properly in the stock holes; the frames were the wrong shape.
I had been prepared for some reversals. The answer to this problem was deceptively simple: I simply used a hammer to modify the shape of the speaker frames so that they would fit. That done, I was then able to bolt the new speakers in place without cutting anything.
I turned the stereo up past 20 without any distortion from the speakers. Excellent.
Thinking about the conversation I quoted above, I remembered more of it; here's how it went:
Me: The, uh, uh...
Friend 1: Penis?
Me: Yeah. The penis. The penis rotted away, so the speaker was shot.
Friend 2: Couldn't you have replaced the, uh...?
Friend 1: Penis!
Friend 2: ...the penis?
Me: Well, there are companies which can do it, but it would probably cost as much as a new speaker would....
Sometimes I really have to wonder about my life.