My question is, could I put a 4 ohm woofer to replace the 8 ohm woofer and still power it with an 8 ohm amp?
The answer, like so many others, is that it depends.
Chances are your amp isn't exclusively capable of driving 8ohm. So, a 4ohm woofer might be okay.
However, if there's a passive crossover in there, then the chances are that it's designed to work with the original 8ohm woofer. Crossovers rely on the speaker being a particular impedance to function correctly, so changing the woofer impedance will mean the crossover isn't aligned well and the results will be unpredictable.
I'd say that more information would be useful. Some questions to start you off:
- Which speakers?
- What did the previous woofer die of?
- Which amplifier are you using? Is there any EQ or limiting involved in the signal chain?
Chris