DIY Internal bracing for NHT 2.9

You also may want to look into Black Hole 5 or No Rez products. I used Black Hole 5 very successfully to accomplish what you want to do. The good thing is you just add what you need.

Go here to learn more.

http://www.gr-research.com/catalog.htm

Personally, I know just what you mean about the bothersome resonance.

A close friend of mine who is probably the most respected loudspeaker modder in the industry almost ALWAYS makes addressing this issue a prime focus of his efforts. He uses Dynamat (whatever the best one is these days) on the inside of the cabinets. However, he cautions to not use TOO much, as you don't want to remove the soul of the music. The Dynamat will give you superior dampening to the fiberglass rods.

Needless to say, he's a very creative and talented person. One who eschews the conventional wisdom in favor of what he has found to produce the best sonics.

Don't do it. Narrod is right, as you'll simply be shifting the resonance to a higher frequency. If the resonance is too offensive, sell them.

It sounds like a mistake to mean. The drivers were voiced with the cabinet as designed. I suspect you will be unhappy with the results.