Subwoofer VS. Box Volume

[johnacaldwell]

I just bought a Polk MM1204 car subwoofer. The sub calls for .88 cu.ft of space. My older box has internal volume of 1.3 cu.ft. Will the sound be degraded if I place this sub in this box or should I buy a smaller box? Can the old box be "filled" to make it a lesser volume so it will work?

[TNRabbit]

Is the .88 absolute or ideal? You could always put a ball in there to fill space...