Can I seal my subwoofer (computer speakers)?

Umm...

I've never had these speakers... but had the Creative T10 speakers before - and I ripped it appart to use the parts for a DIY project.. In the T10, there was a vent -hole too, and in the right speaker was the amp. This amp had a large heatsink that was using the vent as aid for the heatsink to breathe.

I can confirm that the amplifier is residing inside your subwoofer. And the thing is, most of the Creative series use an internal heatsink.

Can you check on the back of your subwoofer: if there is a metal heatsink there - visible... then you can plug the hole - no problem. But I suspect that it is inside. If it is, then the hole is acting as a venting hole for heatsink purposes as well as venting for the subwoofer sounds.

Mark is right with position adjustment. This may solve your BOOMY bass issue. But if it doesn't, then try this:

roll up a small magazine... then stick it into the hole. This will lessen the amout of air that the port is releasing --- and effectively, limiting your boomy issue. What this does is actually making the hole smaller and also extending the air travel [as the magazine will not go all the way in].

It may look odd - with a magazine sticking out of it, but hey, at least there will be no heat damage to your system, and if you have the sub hidden, noone except you will know about it.

Hope this helps!

No. It won't damage the unit if it is not an air vent to keep the sub cool. Before you try covering up the hole, move the woofer and speakers around. It could be the room as much as the speakers. All computer speakers are near field speakers, another words a nearby arms length sound system. They are over achieving beyond that point. It could be bass settings on the computer or the influence of an equalizer altering the sound of your music.

Best.