Clipping problem?

Quick correction - A ported box doesn't provide more power to a sub. It does have the ability to be louder at chosen frequencies if it's designed right. It also can blow speakers easier. If you had a loud signal below the tuning frequency of the port, the sub would have unloaded and there's a good chance it would have exceeded it's excursion limits - blowing the spider loose. You should be much safer ith your sealed boxes now.