Im using 4 ohm 8" woofers as replacements in boxes meant for 8 ohms. So if I hook the woofer straight to the post and not using a crossover. While leaving the Midranges and tweeters hooked to their crossovers, would this be safe and sound okay?
As per Ohm's Law, the current flowing thru the 4 ohm voice coil will be twice what it would be if the impedance of the coil was 8 ohms. The louder you play, the greater the current. It may eventually burn out the voice coil.
the voice coil is made for the current of the 4-ohm load. I'd be more concerned about the amp blowing parts inside, releasing magic smoke. or choking if it's got a current-limiter. and generally sounding like crap if it hits said limit.
Don't really want to do that. The overall impedance the speaker will present will be less than 4 ohms if you just hook it up to the posts because the mid/tweeter is hooked up in parallel.
From a sound quality point of view, it'll be a mess of problems as a decent crossover is more than just a high/low pass filter. It can also adjust the sensitivity of the driver and provide other filters such as a notch filter. Also, you don't want too much overlap between drivers.