Sealing ported enclosure to reduce boom

Depends on the speaker, but if you have a three or more way speaker and multiple ported chambers, you could have some frequencies drop out if the mid woofer driver/crossover combo is "looking" to the port for bass reinforcement. Probably not common, but possible.

There is a very fundamental theory of room acoustics which no one has mentioned yet. Place the speakers at one of the room nodes and see how the boom reduces drastically. So how do you find out a room node ? It is simple, play a bass track which typically has an overhang in your room. Connect one speaker at a time (disconnect the other speaker). Stand next to the speaker that is playing, move around the speaker listening for the location where you hear the maximum overhang. You can just move within a radius of 1 foot form the existing location of the speaker and find out the spot of maximum bass/overhang. Once you locate it, place the speaker right at that spot. Repeat the same for the other speaker. You may have to move them inches to get the right imaging but for sure your bass issues would be reduced. You may even do this for one speaker, which you think is causing the maximum boom, this also you can ensure by playing a single speaker at a time and listening from your sweet spot to determine which speaker is causing more boom. Do it for that speaker, keep it fixed at that location and move the other speaker around for imaging and staging. Try it !!

didnt bother to read the other posts, but you do realize that you paid your monies for the design of your spkrs, therefore then you realize that your spkrs were designed to have a port, for a very particular reason....boom is most likely a result of your placement of your spkrs w/in your room. move them away from room boundaries? seems obvious.

I had a pair of B&W's with what they called "bungs." I always got a kick out of that one. Seriously though, can every speaker have it's port sealed off? Could this damage a woofer in a design that was intended to "breath" more.

Agree with Pani. Try using the Sumiko Master Set method to set up your speakers. It will take a while but you will learn to find the bass nodes in the room and correct for any boominess.