Will 8 ohm sub woofers work with a 4 ohm amp?

if you put 2, 8 ohm speakers together on the same channel you will trick the amp into seeing a 4 ohm load, it is not advisable to run a 8 ohm coiled speaker on a 4 ohm amp unless you do the above. So if you want to run 2 8 ohm speakers from a 4 ohm amp this will work the best although the amp will need to be hefty as its worse to underpower a sub than overpower it! I have used a 8 ohm speaker myself on a car amp and had no problems but it was not a cheap entry level amp! some amps will take it, others will get hot and enter protection mode. Hope this helps!!!