If the driver's made for one, usually a ported enclosure will hit lower than a sealed =, if made properly. You can get great SQ out of a ported box, but sometimes it can get a little boomy. You also get higher SPL ported. This is very driver dependant, though. The Alpines can handle much higher than what they're rated for. They can get great SQ in a small sealed box, though they also sound great with a larger ported enclosure. I'd go sealed with the JBL 1200.1. The JBL doesn't have a sub-sonic filter, so if you built a ported box, this is one thing you'd have to consider.