is a crossover required on a sub?

I have a friend and I want to use his sub for a test. it is a passive sub(no amp) from a car. he thinks that the sub will need a cross over to avoid distorting or something.. I have tried to asure him that the sub by design has a natural roll off point and that it will not be damaged by highs.. can I get a vote on this or something to convence him that everything will be ok.

it is an acoustic suspension box

As you say, the highs fed to the sub won't harm the subwoofer but, what you don't say is that the sub will still try to reproduce them and it will sound like muddy drek and it will draw attention to it. Your "by design "rolloff" (not cutoff) won't prevent this.

If you're using a HT receiver with an adjustable LFE/sub out you might get by but remember, you'll need a power amp then.

I understand that it will sound like poop, I'm just testing a theory. I have a power amp, but not a sub out.. it's hard to explain.

anyway, you are sure that it will not harm the speakers in any way.

Yeah the highs won't harm the speaker at all, just make it sound like turd.

turd indeed...
I've done this to see if old speakers still work...
thats about all this type of testing is good for...