Sealing ported enclosure to reduce boom

An in-between solution would be to change the port dimensions and thereby lower the tuning frequency. If you make the port longer, or narrower, the tuning frequency will be lowered and the bass will start to roll off higher up and more gradually. A slightly smaller diameter tube can be inserted into the port (ring the inner tube with electrical tape in two places to get a good friction fit). This smaller tube can be longer than the original port. Or, you can do it with straws, as long as they are likewise longer than the original port. Pack the straws in tightly until they deform into a honeycomb-like shape. You will probably have to remove the woofer if you do the straw-pack, so that you don't accidentally push the straws into the enclosure and end up with a pile of straws at the bottom.

How long should you make the insert? As long as possible, leaving about one diameter of clearance from enclosure walls or woofer magnets (like if the insert is 2" in diameter, you want at least 2" of clearance). If the bass is still boomy, go ahead and seal the box. If you overdid it and the bass is now too lean, the shorten the insert.

Duke
dealer/manufacturer

I agree with the "bad idea".
I have tried it mulitple times over the years, and agree with Knownothing.
Speakers are designed for a purpose, either ported or sealed.
You really won't get the both of best worlds in home audio anyway (alot of full range car speakers are infinite baffle designs and work good ported or sealed).
When I tried stuffing the ports in the past, I gained nothing, and lost alot as far as soundstaging, and bass goes.
Nothing wrong with ported speakers provided they are set up in your room properly.
If you have problems with ported designs, its either that your room has problems, the position of the speakers, or the port is in the front and you are listening near field.
I am a sealed speaker man myself (I (insert heart here)) love my NHT M6's, provided there is good amplication available.
Nothing at all wrong with ported speakers, just experiment to find the best placement.
I have a feeling thats the only problem with your speakers.

There aren't many placement choices when I room is 13x15. Speakers can only be so close to you. The Cardas site recommends (width of room)x(.447)=distance of speaker front to rear wall. That would be 5.5' for me almost putting them in the middle of the room.
I stuffed the ports and they sound pretty good, much better then when I first auditioned them. But maybe there could be some adverse effects when the woofer is sucking in air thru the port. It might not have enough air available to push as per design.

I like Duke's ideas!

I've seen the port diameter trick done professionally to improve performance.

Never tried the straws approach but it sounds good!

What did you stuff the port with? If you think it sounds better you should find some porous foam material and cut it to fit properly. That should work without any negative side effects.