Protip: Using a sub? Plug your mains

You need to be able to control the rolloff of the main speakers. You cant do that by just plugging the port. Some woofers dont work well in sealed boxes. What you really want is a high pass filter. That will enable you to tune the rolloff point and slope so that it integrates with the sub. And it will also prevent any issues with excursion below port tuning frequency. If you follow eriks advice, you will end up stressing the driver cone as all you are doing is causing the driver to be pushed against the air pressure in the box and stressing it. 

On the other hand if you dont listen to heavy bass music then it doesnt reallly matter whether you plug the port or not. 

Some drivers can handle both ported and sealed enclosures, some cannot. Also, when plugging a port, you want to plug the whole length. That applies to more than just speakers ;-)

Isn’t that we have crossover slopes in both the sub and main speaker to ensure a smooth handoff of the frequency?

Hey @testpilot - So main speakers have their own natural rolloff and that a lot of audiophiles forego the use of, or can’t, put an electronic high pass filter in line with the main amplifier. As a result, the main speakers go pretty low and the bass can get messy. By plugging the port you raise the -3 dB point, letting the sub handle more bass.

The critical thing, for me is this: By plugging the ports you prevent excessive excursion below the port frequency, hopefully reducing distortion. This benefit exists whether or not you use an electronic high pass filter.

If you are using an electronic high pass filter this becomes less of an issue.  I'm doing a project soon I hope to better document why this work.  Stay tuned.  I have lots of solder and breadboards to go through. :)

Makes perfect sense to me. The driver ends up operating more in line within its capabilities, reducing heat and distortion. Every little bit helps.

All the best,
Nonoise