Originally Posted by jcurrie
What would sealing the port do? Can that damage the drivers?
Sealing the cab will allow the driver to be loaded to the lowest notes of your instrument. As a result, cone motion will be considerably less. Sealing a high-tuned ported cab may actually result in a fuller, more pleasing bass. However, without TS parameters and box volume, there is no way to tell without trying. Of course, how you feel about the resulting tone is a matter of personal preference.
Sealing the cab is a good place to start. If you prefer a tone between sealed and ported, that's when to try adding insulation to the ports. Listen to the resulting sound and watch those cones for over-excursion. The more insulation you add, the closer you get to sealed.
There are two common ways to damage a drive: 1) over excursion, and 2) thermal overload. By sealing the cab cone motion will be reduced for the lower notes. The amp manufacturer generally selects the drivers to be safe from thermal overload with the included amplifier. It is sometimes the case that large amounts of bass boost can cause over-excursion (farting out). As a musician, you need to always be aware of the sound quality coming out of your speakers. If the speakers sound stressed, it's time to cut some bass or volume.
Edit: Just a last minute check - how much excursion are you seeing? Roughly, a 1/4 inch, 1/2 inch, etc., and at what volume? Don't pay attention to the dial position. How loud is it? Also, have you checked to verify that 1) the drivers are securely screwed down (no air leaks), and 2) that the port tubes are properly attached - sometimes the cardboard tube extension (off the plastic rim/flare) actually comes off during shipping and is lying lose inside the box.